FORM FIVE: ENGLISH LANGUAGE-TOPIC 1: INTRODUCTION TO LANGUAGE  

TOPIC 1: INTRODUCTION TO LANGUAGE  

LANGUAGE:
1.   Language is a symbol system based on pure or arbitrary conventions…. (syane and jindal
2007:1)

2.   Language is the institution whereby humans communicate and interact with each other by means of habitually used oral auditory arbitrary. (Hall, 1969 (ibid)
3. Language is a system of arbitrary vocal symbols by means of which a social group cooperates (Bioch and Trager, 1942)
4. Language is a system of vocal symbols used for human communications. (wardaugh- 1972)
5. Language is a collection of signs which are arbitrary chosen and organized according to certain fixed principles that are acceptable by the society.
6. Language is a system of arbitrary vocal symbols by which thought is conveyed from one human being (a speaker or writer) to another (a listener or reader)
7. Language is a conventional system habitually system of vocal behavior by which members of a community communicate with one another.
8.   Language is a learned and shared habitual system of vocal symbols through which human beings in the same speech community interact and hence communicate in terms of their common cultural experiences and expectations.
9. Language is the system of communication in speech and writing that is used by human beings.

 NOTE:- with regard to the above definitions, the most possible definition of language may be this “Language is a system of arbitrary and conventional vocal symbols through which
thought (message) is conveyed from one human being to another i.e.: from the speaker or order to the listener or  reader.

ELEMENTS OF LANGUAGE

The definition of language consists of several key terms/elements as follows.

1. System

(a)     Language is a system in the sense that it is a collection of sign or symbols i.e. It assembles together the smaller units to form the larger units and these units are arranged in a regular order for example:- phonemes-syllable-morphemes-words-phrases-clauses-sentences-paragraph-comprehension.

(b)     Language is constituted by several elements which are arranged in a regular fixed order, such elements include subject, verb, object, complement and adverbial.

For example: – The boy has been here since yesterday

S          V                     A         A

He left your book in my room last week

S     V           O             A               A

(c)      Language being a system is also constituted by various subsystems such as sound system, structural system and meaning system.

2. Arbitrary

The arbitrariness of language is proven by the following facts.

(a)  In language there is no correspondence (similarity) between the symbols (sound or letters) and the realities, meanings or objects which are represented by those symbols.

For example: – the word dog with the four legged animal, table as a piece of furniture.

However language is arbitrary due to the fact that the linguistic symbols used in language were just picked haphazardly (with no particular plan or organization) i.e. there was no any formal meeting by any speech community which sat to form language. Each speech community has its own symbols representing different realities.

3. Vocal

Language is said to be vocal since each language is based on speech sounds that are produced by the vocal organs, (organ of the mouth, nose and throat) i.e. in spoken form language is presented through the vocal sounds (sounds from the mouth)

4. Symbol

Language is symbolic in the sense that language uses signs or symbols to represent realities, object
or ideas.

There are two major types of symbols used in language

(a) The acoustic images (the sounds)

(b) The graphic signs (orthography letters 1 spellings)
These symbols represent realities, objects or ideas in spoken language; we use the acoustic images (sounds) where as in written language we use the graphic signs (letters)

5  Conventional

Language is conventional due to the fact that any human language (system of communication) ought to be mutually acceptable and understood by a particular speech community i.e. all members who use that particular language.

6. Message

Message is the key word language has the message since it is the message that is conveyed from one human being to another i.e. language is used as the medium through which ideas, opinions or thought is carried from the speaker or writer to the listener or reader. The participants in language communicate the message to each other thus message is the central element in any communication system (no message, no communication)

7. Human being

Language is used by human beings i.e. it has been proved that it is only the human being among all creatures who communicate by the use of language other creature do communicate using different systems or forms but they never use language as there means of communication.

 

           A LANGUAGE/A COMMUNITY LANGUAGE

          A LANGUAGE is a specific from (system) of speech which is conventional and mutually understood by a specific speech community i.e. it refers to one particular language as used and spoken by a particular community.

The speech community can be ethnic group, a tribe, a nation or even the whole continent for example Kichagga is a language of chagga people of Kilimanjaro region, Kingoni a   language of ngoni as a tribe,Swahili a language of Tanzania as a nation, English a language of Europe, America and Australia as continents.

    Features of a Language

A language has several features or characteristics:-
1.  It is a specific concept referring to one particular form of speech (system of communication) that is mutually used and understood by a particular speech community.
2.  A language is used to express the culture of a particular speech community i.e. a language is the central element of a particular culture hence a language and culture are
inseparable.
3. A language changes and develops with the change and development of culture i.e. dynamism of a language is usually influenced by culture.
4. A language can also change on contact with the foreigners through different activities such as trade, tours, colonial domination etc.
5. A language usually may have script (forms or spellings) different from other languages i.e. each language has different orthography spellings.
6. A language may have phonological and grammatical systems (pronunciation and structure) different from other languages.
7. A language may belong to a group with other languages which stem from the same ancient language for example Kiswahili, Kisukuma, Kihaya, Kinyakyusa etc are among
the Bantu languages hence each language belongs to Bantu language.

THE BASIC DIFFERENCE BETWEEN LANGUAGE AND A LANGUAGE

1.    LANGUAGE Is a universal concept i.e. it refers to all language in the world as used by human beings.

          
          While

A LANGUAGE: – Is a specific concept i.e. it refers to only one particular system of Communication that is used by a particular speech community.

2. Language does not belong to a particular speech community i.e. It doesn’t have any specific group of
   people who regard it as their own it belongs to all human beings in general.

While
A Language belongs to a particular speech community that uses it as the means of communication among themselves. I.e. a language is owned by a particular speech community e.g. English by the British, French by the French etc.

3.  Language has no link with the culture of a particular community i.e. it cannot be used to express the culture of one particular speech community.

While

A language has a direct link with the culture of a particular speech community that uses it i.e. Each particular language is used to express the culture of the people who uses that particular language e.g. English for the English culture, Swahili for the Swahili culture etc.

4. Language is static i.e. It doesn’t change with the change of culture and contact with foreigners.

   While
   A language is dynamic as it usually changes and develops with the change of culture as well
as the contact with foreigners.

           UNIQUE PROPERTIES/ FEATURES OF HUMAN LANGUAGE

Human language has a number of defined properties which uniquely distinguish it from communication systems (form) of other creature such as animals and insects. i.e. there are several features which are uniquely manifested (found) in human language and are unlikely to be found in the communication system of other creatures, this acts as a prove to the fact that it is only human beings who communicate through language where as other creatures do not use language as their means of communication.

The following are the unique characteristics or properties of the human language.

1. Duality/ Double articulation
   Human language is organized or produced at two levels simultaneously
          (a)  Sound level at which human beings are capable of producing the individual sounds which do not convey any intrinsic meaning when they occur separately.
   (b)  Grammatical/ structural level at which a human being produces the Meaningful units such as words or phrases.This is achieved when the sounds combine together to form the
   meaningful and grammatical units such as words or phrases.At this level it is possible for the same sounds to form different words with different meaning
   for example /i, b, n/ can combine to form nib and bin /e, t, a/ can combine to form eat, ate, tea.Thus with a limited number of distinct sounds, we are capable of producing a
   very large number of words which are distinct in  meaning. This makes human beings economical in the use of language. This feature cannot be manifested in the communication
   system of other non-human creature i.e.There signals are used at only on level.
2. Productivity/ Creativity

This is the feature of all human languages that novel/ new utterances are continually being produced or created i.e. language allows speakers or writers to produce and understand new utterances/ sentences that they have never produced or heard before.
This implies that due to the use of language, human beings are capable of producing and understanding the new sentences produced by others.
This makes human language dynamic because all the time he or she strives to produce or create new words, sentences or an utterance that is being understood by both a speaker or writer and the hear or reader.
However at childhood, children try there level best to produce new utterances or words. The features that cannot be found among communication systems of other creatures, these creatures produce the signals that are usually static i.e. they are the same and this cannot be produced in other forms to communicate experience and events.

3. Arbitrariness
          All human languages have arbitrariness in the sense that there is no direct or natural connection or similarity correspondence between the linguistic symbols and the message,
   meaning or concept being represented by those symbols. I.e. the linguistic signs or symbols have arbitrary relationship with the reality or meaning (objects or concepts) they
   represent or indicate. For example the word table has no similarity with the object known as table.However for the majority of animal signal, there does appear a clear connection
   between the convey that message. For example a hungry cat produces the cry that represents the actual state.
4. Interchangeability/ Reciprocity
          Human language is unique because any person using the linguistic system can both send and receive the message. I.e. human language allows communicator to join here exchange
   position. At one time the communicator is a speaker and a listener at another time. This imply that when one person is talking, the other is listening and when the listener starts
   responding, he or she becomes the speaker and the person who was previously a speaker becomes a listener.However this feature cannot be manifested among other creatures
   because there is no room for animals and other creatures to interchange positions as they usually produce their signals at the same time.
5. Displacement
          Human language is displaced in the sense that the human language users (human beings) are capable of producing and understanding the message in relation to time and place. I.e.
   Human beings are able to communicate the message of the events of different times and places. This means that   human beings can convey the message of present, past and future
   time as well as the message related  to the event taking place at different places or locations e.g. distant event such as football match in England.
   However with human language human beings may convey the message on both concrete and abstract phenomena. This is due to the fact that, animal communication lacks this
   property as they can only be able to produce and understand the message in relation to only the immediate time and place.  I.e. they can convey the message on the event happening
   now and here but not yesterday, tomorrow and there.
6. Cultural transmission/ learner ability

This is the process whereby language is passed on from one generation to the next. I.e. human language is transmitted from one individual to another not by physical inheritance but by learning – Human language is not inherited genetically from parents instead it is acquired or learned depending on the environment to which one is exposed. That why we say language is culturally transmitted from one duration to another as it is acquired in culture with other speakers and not from parental genes.
This implies that any human language is acquired through learning from one generation to another. I.e. Every person gets language through learning but not through inheritance from parents.However the general pattern of animal communication is that the signals are instinct/ inborn and there are not learning i.e. Animals and other there signals instinct without learning them.

7. Specialization

Human language has the feature of specialization in the sense that every society has its own physical and social experiences which determine how the society sees its physical world i.e. the language of a respective society would tend to describe and reflect the physical features and social experiences which only exist in that society. This is proven by the fact that it is very difficult to translate one language into another since experiences in each language is different.However communication systems (signals) used by animals and other creatures cut across the whole species of animals without specializing to a particular group of the same species.

8. Discreteness

The sounds in human language are meaningfully distinct I.e. the sounds used in language are only meaningfully especially when they are part of a language. For example the words pig and big differ due the presence of /p/ and /b/, ten and pen differ due to the presence of /t/ and /p/
This implies that each sound in language is treated as discrete.

9. Reflexiveness

This is the feature which enacts that human language has the ability of talking about itself.
For example we are now using language to talk about language this property of language by which human language talks about itself is what is referred to as reflexiveness.
However it is not easily imaginable that animals are able to cry about their cries so this property makes human; language different from human communication.

Competence and performance in language
Competence refer to the knowledge of the whole language i.e. the ability not only to apply the grammatical rules of a language in order to grammatically correct sentences but also to know when and where to use those sentences and to
It also means the subconscious ability to judge the grammatically of expression as used in a certain language.

NB: The communicative competence includes the following
1. The knowledge of grammar and vocabulary of a language
2. The knowledge of rules of speaking and knowing to communicate according to topic and speech events

3. Knowing how to use language appropriately i.e. Using language according to social setting the relationship between speakers as well as according to a particular occasion
   performance refers to as the actual use of language in concrete situation. It is determined by choice of writing words suitable for the right situation. It also refers to the
   actual use of language by individual in speech and writing i.e. the ability of a person to use the knowledge of language to produce and understand the sentences without
   necessarily adhering to grammatical rules.

              NB: Competence and performance go together due to the fact that competence proceeds performance. Competence gives corrections to wrong expressions through
performance. But there are times when the two are not connected as one can have performance without competence and vice verse.

IMPLICATIONS OF COMPETENCE AND PERFORMANCE

–  To show that our ability to use language is governed by certain intuitive capacities. This is the reason to why native speakers of the language is capable to say whether the
construction is correct or not even if they are unable to explain it technically.
– It also shows that language ability of an individual can be improved through the use of appropriate methods of language teaching.
– Uses of the language have more in their linguistic stores than what they produce. This is due to the fact that language performance is affected  by the number of factors such
as illness, tiredness, stress, etc
–  Likewise it shows that language is governed by rules. As it is common for the language users to correct errors and mistakes in different constructions of language.This is
made possible because intuitively we are embedded with those rules

            FUNCTIONS OF LANGUAGE

Human beings can use language for different purposes,The following are the major function of language

1. Referential / communicative function
   This is the use of language to convey factual or non-factual information
   I.e. human being use language to communicate with each other to pass information from each other     .
2. Expressive or emotive function

This is the use of language to express feelings, emotions or attitude. Man can convey his emotions by screams, grunts, sobs and gestures,but still needs language for confirm or
elaborate those signals. Thus report feeling or attitudes of the writer or speaker or of the subject, or evokes feelings in the reader or listener fall under this function.

3. Cognitive or Directive function

This is the use of language for the purpose of influencing the behavior of others e.g. to command them to do something, request them warm them. Thus language is used for the
purpose of causing (or preventing) overt action. This is the most important function of language, it impart factual information and commands. Passing information is absolutely
necessary e.g:- asking and answering questions, reading instructions etc.

4. Phatic or interrogation function

This is the use of language to establish or maintain good social relationship among human beings
E.g. Greetings, cheering-up etc. Uses phrases like “nice day today”, “how do you do”. Think of this situation; Gorge coughs.Then his friend Musa says “Bless you”. This has got
no any informative content but intended to link people and make coexistence peaceful and pleasant.

5. Poetic or athletic function

This is the use of language for pleasure of mind (asthetic) use language in its beauty pleasure.
I.e. language is used for entertainment
e.g.  Reading a certain literature for enjoyment, language used in theater for performance – the use of language in artistic way.

6. Meta linguistic function

This is the use of language to talk about language.
I.e. Language for its own sake or the use of language to explain other language concepts.
E.g. we are now learning language.

Other functions

7. Imperative or Declarative

This the use of language for the purpose of declaring something
E.g. Language used in ceremonies, meetings, courts of law, church masses

8. Regulatory function

Use of language for the purpose of warning or imparting discipline to the people been spoken to and thus used in order to win peoples respect
For example the language used by religious leaders

LANGUAGE POLICY IN TANZANIA

This language policy in Tanzania states that Swahili language shall be used as the medium of instruction at the primary school level and English remain the medium of instruction from secondary level to the university level.
The government has accepted both English and Swahili to be used as official languages.
However, the status of English is confusing as it is in transition between being the foreign language and the second language that makes even Swahili in the same transition between the second language and the first language.

NB: the use of either English or Swahili as the medium of instruction has created a very hot debate since there people who support English where as
other support Swahili.

ENGLISH IN SCHOOLS

At present English is used as medium of instruction in secondary schools and higher learning institution. But there is a debate on whether English should continue with the status it has or it should be replaced by Swahili. Let us see the different arguments people have about English out to be replaced by Swahili today.

Those who support the current English status.

Some of their points include the following:

1. English is a language of today’s world business so Tanzanian. So Tanzanian have to learn through it in order to function in today’s world.
   2. English is a well developed language due to its long history. Swahili lacks some important vocabulary especially in science and technology.
   3.    Many books are written in English, so learning through English it is easier and less costly than turning to Swahili. This group of people is
   afraid of change because people think the government has no money for changing the medium of instruction.
   4.    English is everyone’s property today. It is no longer colonial language. It is spoken in different parts of the world so there is no justification
   of equating English with colonialism.
   5.   Learning through English makes a child divergent in class. A person who speaks many different languages is like a person who is living in
   many worlds because each language looks at the world differently from other languages. So children should learn though English so that they can explore.

   People who propose the use of Swahili.

The following are some of the points made.

1. English language is a foreign language making students learn through a foreign language is like colonizing their minds so we should get   rid of their colonization.

2.Students learn better when they use the language they know well. Unfortunately Tanzanians do not know English well so making them continue learning through it endangers education in Tanzania.

3. Experience from developed countries reveals that students learn using their countries languages and English or other languages are learn as subjects but the medium of instruction is Korean (Hangul) these people are technologically developed. They are the ones who export television and other electronics products.
4. English should be taught as subject like the way French is taught. This will improve its teaching. Currently English is very badly taught so the appeal is to improve the teaching of  English.
5. Swahili is the language of African identity so we ought to teach using a lot if we are to cherish our heritage
6. No language is endowed with scientific knowledge so it is a myth to believe that English is the language of science and technology. Any language including Swahili can be a metalanguage of science and technology.
7. Already teachers are using code mixing. If you observe many classes you will discover that teachers speak a lot of Swahili in the class room.
   So we need to formalize that use of Swahili.

From the argument of both groups, it seems there is a language problem in Tanzania. It seems both English and Swahili are needed. The problem is the status each language is to have. We may argue here that it is possible to teach through Swahili from primary school to University level that will be possible if the government changes its language policy in Education.This may be possible without endangering English. However there has to be some well trained teachers who will teach English.
Translation of the existing literature will not be necessary if English is taught well; this is because students who learn through Swahili will also master English provided it is taught well. Having very competent teachers is an investment so there should be purposefully effort to effect the change.

       A LANGUAGE/ SPEECH COMMUNITY

This refer to a group of people who share or regard themselves as sharing the same language or language variety i.e. it is a group of people who mutually understand and hence can speak and use one particular language. For example Swahili language community of East Africa, Bengali language community of Bangladesh, Hehe language community of Iringa region.

       LANGUAGE VARIETIES

What is a language variety?
A language variety is any kind of language or any particular kind of language which arises according to difference factors such as the use and the user. Basically language varieties arise due to two basic factors i.e. the use and the user.

There are two major language varieties:-

(a)  Register

This is the language variety which arises according to the use.
These determine by several factors such as occupation, field of discourse (Topic), Tenor of discourse (status), mode of discourse (media), Modality (channel), Doman (Function).

     (b)  Dialect

This is the language variety (variation) that arises according to the user. This var111iety is determined by several factors such as social class or social group, geographical area or location, age, sex, profession etc.
Dialects differ from one another in terms of vocabulary, pronunciation (accent) and grammar but the most noticeable feature is pronunciation (accent)

TYPES OF DIALECTS
There are three major Dialectical varieties of a language.

   (a)  Sociolect / Social dialect

This is the language variety (type of dialect) which arises according to social class or group i.e. it is the variety of language which used or spoken by people who belong to a particular social class or group such as high class us middle class low class, educated us non – educated, initiated us non – initiate the rich us the poor. The grouping of people into different classes is marked with regard to education back ground, economics status as well as traditions and customs.

   (b)   Geographical / Regional dialect

This is the variety of language according to geographical location or area i.e. it is the variety of language as used or spoken by inhabitants of a particular place, part or geographical location, for example British English, American English, Australian English, South African English, akwngusa vs Kipemba, Scottish vs Kimachame vs Kirombo vs Kimarangu vs Kibosho.

   (c)  Idiolect

This is the language variety which arises according to an – individual personal i.e. It is the variety of a language which is used by an individual person in speech or writing
NB: The Individual variety of language is mostly marked in terms of diction (choice of words) the command of language as well as the accent.

     THE BASIC DIFFERENCE BETWEEN A LANGUAGE AND A DIALECT

A language and a dialect differ in the following ways

(i)  The difference in size

A language is bigger than a dialect in the sense that it has more speakers than a dialect. At the same time a language is spoken in a larger area than that of a dialect, for  example the number of English speakers in general is bigger than that of south Africa English likewise English language is spoken in more than one continent but American English is spoken in America.

(ii)  Difference in prestige  status

A language is more prestigious than a dialect i.e. it has a higher status than the status of dialect – people feel better/ prestigious when they are said to speak a language than when they are said to speak a dialect. For example English speakers feel better than the American English speakers.

(iii)  The difference in mutual intelligibility:

Mutual Intelligibility is the stake in which a language or dialect is mutual understood acceptable by all the members. This implies that dialects are mutual intelligible than languages i.e. speakers of different dialects of the same language can understand each other whereas the speakers of different language cannot understand each other. For example speakers of American English and British English are mutually intelligible since the two are the dialect of the same cannot understand each other because the two are different languages

NB: Dialects differ from one another in terms of vocabulary pronunciation (ascent) as well as grammar.

CAUSES OF  LANGUAGE VARIETIES

What causes language variation?

There are several reasons for language variation the some of them as follow;
Geographical differences.

Geographical extent is one among the causes of language variation as people who live in different geographical area tend to speak differently from each other. The natural barriers such as mountains big rivers and huge forest are among things that lead to language variation, this is due to the fact that shay affect contacts from one side to another. Geographical distance can be region wise i.e. within one country b (from one region to another) or National wise i.e. One country and another. For example Nigerian English, American English as well as British English, because of limited contact between those countries each country will speak her own language variety.

Occupation.

People of different occupations have different language styles. As the lawyers use language which is characterized by special term and use long and complex sentences in their legal documents while the language journalism is different from that of the lawyers as the journalist use embellished language and their sentences most of the time starts with adverbial elements. Normally each occupation group has their own jargons which differentiate them from another group. Those jargons can only be understood among people of the some occupation. For example adjourn Commence, mutatis mutandis are the jargons which are dominant in legal language.

Age differences

Also these cause language variations as people of different age have different language habit as a result they tend to use language in different way. The children use simple language and sometimes ungrammatical because they have not yet.- Mastered the language. While the youth tends to us slang which is less preferred by elders, the differences we observe among these language users lead to language variation.

Sex differences.

Women and men show significance differences in language use. Some of these differences are physiological and some of them are sociological. Physiologically women use high pitch while men use low pitch as a result of vibration of vocal Cords. Socially there are words which are highly used by men and there are those which are used by women. Sometimes men tends to use unpleasant words (rude/ harsh) in an case way while women tend to be very selective in their diction (choice of words) As a result the two groups leads to language variation.

Social classes.

Normally the society is stratified, now the classes which are found in our society tend to have different language style for example the class of workers have their own language style which is different from the class of farmers likewise the class of educated people is said to use the standard language while uneducated class use non – standard language

Individuality/ idiolect

This refers to individuals language habits that make one language user to be different from other users of the some language. This is determined by the individuals choice of words, having particular voice quality, use of certain expressions and the use of Paralinguistic features An individuality mark the identity of someone hence you can be able to say that someone is speaking as you already know his or her style. Having those individual features which differentiate from one language user to another user of the some language, leads to variation of language.

Basic concept of language

(a)  First language (Mother language)
      This is the language that a child acquires from his or her parent / family at the childhood such as a language is not learn but it is only
acquired by listening and imitating. Once can know how to speak it but not to write it. For example Kingoni of the Wangoni, Kihehe of
the Wahehe, Kinyakyusa of the Nyakyusa.

(b)  Second language

This is the language which is learn after the acquisition of the first language. This language is usually     learn formal at school through
drills organized and supervised by the teachers. For example Swahili in Tanzania and English in Kenya, Uganda and Zambia.

 
(c)  Foreign language

This is the language that has been adopted and hence used or spoken in a particular country from another country it is the language used
or spoken outside its original  native speakers (used or spoken by non – native speakers) for  example English in African countries, French
in African Countries, Swahili in American or European countries or some other African countries.

 
(d)  National language

This is the language that has been selected and accepted by the government so that it should be and is being used as the major tool of
communication by the majority of the people within a particular country or a Nation.

It is the language which is widely spoken in the largest part of the country.The National language ought to be one of the official language
in the country and also needs to be a standard language.

The National language likewise ought to be the medium of instruction at any levels of education in the country. For example Swahili in
Tanzania,English in Kenya, Zambia, Uganda, Liberia etc. French in Cameroon, Senegal, DRC Congo, Gabon etc.

 
 (e)   Official language

This is the language that has been selected and accepted by the government that it should be used as a tool of communication in all
official matters and public places within the country such as in the government officers, school, hospital, courts of law, parliament etc.

An official language must be standard i.e. the one with uniform spellings, structure and pronunciations for example Swahili and English
are the two official language in Tanzania

(f)  Standard language

This is the language which has its own orthography (spellings), structure and pronunciations modified so that they are the same wherever the language is spoken or used i.e. the language with uniform spellings, structure and pronunciation.It is the variety of language which is generally taken as prestigious recognized as correct and acceptable grammatically lexically and phonologically.

The standard language or dialect is the one used by educated people or the ruling class and the one with high status on speech and writing of the educated   nature speakers of that language.

It is the variety of language which is widely under stood, used in mass media, described in dictionaries and its grammar so taught to the non – native speaker  when they learn it as the foreign language

Features of standard language

1. It is non – localized i.e. It is not restricted to a certain particular region – it is widely spread in different regions.
   2.   It is usually taught in schools as a model of variety especially to the foreign learners
   3.   It is thought to be a dialect of the upper class
   4.   It is a dialect that dominates the media in the world for example Television, serious Newspapers and magazines, radio etc

      
        How is a language standardized

There are several processes that are normally involved in language standardization

     (a)  Selection

Out of many dialects of a language, one is chosen in order to be standardized. The choice is influenced by social factors. For
example the variety that is spoken by a class of people who are considered to be important is more likely to be selected than
other varieties such as the variety of the rich people; the royal family, the upper class etc will be favored in the selection.

    (b)  Codification

This is the practice of creating norm of usage; this is done by writing the grammar of the selected dialect, dictionaries and
encyclopaedia.This process is meant to familiarize people with the variety to be standardized

    (c)  Elaboration

Under this process the role which the standard of dialect will play is made clear. For example the role of dialect in education, management, government etc need to be clearly explained

 

    (d)  Acceptance

At this stage the chosen dialect is voted for normally members of the parliament accept the variety on behalf of the people from
there the language becomes standard.

  (g)  Pidgin

This is a new language which emerges or arises as a contact vernacular between or among people (group of people) who need to communicate but do not share a common language. I.e. it is a simplified kind of language that develops when there is a contact between two groups of people who have different linguistic background and these people have no other language than the two languages they use or speak.

It is an auxiliary language which is formed or arises between or among two groups of people who come into contact to fulfill only certain limited communication needs or purposes. These people have different language (without sharing a common language)

      Types of pidgin

      1.Temporary (Marginal)

This is the pidgin which arises in a speech community and last or exist for a very short time. This may happen between the expatriates and house servants or laborers or among the soldiers from different countries when they are needed for a special task on contract with fixed time. I.e. this language usually disappears after the contact is over.

2. Expanded

This is the pidgin language which exists for a reasonable duration of time and extends its domains of use beyond or outside the spheres of its origin i.e. it is a type of pidgin that develops in the Multi – lingual areas i.e. places that have many languages.
In some countries this type of pidgin is even used in radio broadcast and parliamentary debates and has even become a written language, codified in dictionaries and used regularly in books and news – papers

NOTE: – The origin of pidgin is traced back with regard to the triangular slave trade in Atlantic west Africa and west indies
coasts especially in the trade routes and coastal areas. For example Tok – pisin is a good example of an English base
pidgin used in Papua New Guinea, West Africa.

Characteristics of pidgin

Pidgin has a number of characteristics features as follows
(i)    It is a new language which emerges after the contact of two groups of people who had never met before.

(ii) Pidgin has no native speakers due to the fact that it is a new language that is formed by two groups of people who
already have their own native Language. I.e. pidgin does not belong to any particular group of people who use and
regard it as the native language.

(iii)The pidgin language is formed to fulfill certain limited communication needs or function i.e. it has a limited range of
function as it is formed to cater for Specific or limited purpose such as trade, business, conversation etc.

(iv)Pidgin has a unique grammar with very simple syntactic structure than the lexified language such as it lacks pluralism of
nouns, Concordia a agreement  between the subject and predicate in the third person.

(v)  Pidgin is a temporary language which emerges and exist for a short duration of time when it is extended and exist for a
long time, it is when it becomes Creole.

(vi)    The lexicon (vocabulary) of pidgin is derived from another dominant language (lexified language) which guides the
grammar of the pidgin language.

(vii)   Speakers of pidgin employ paralinguistic features such as the use of gestures, sign etc. this is due to lack enough
vocabulary.

 (h)Creole

This is a pidgin language that arises as the mother tongue of a newly formed community of people who do not share a common language other than an emerging or already established pidgin.

It is the expanded pidgin which has become the mother tongue (native language) of the new members (generation) of a speech community i.e. It is a pidgin that has acquires people who speak it as their first language. This is normally the case when speakers of a pidgin bare children who know other language than a pidgin.

Creole is a pidgin language which has been widely spoken and adopted as a mother tongue of the new generation.

Examples of Creole

English lexified Jamaican, French

Krio – English based Creole spoken in sierra – Leon

Guyana – America

Gullah – USA

Characteristics of Creole

1. It is not a new language it is formed from pidgin. I.e. Creole comes into being through the transformation of pidgin which has
   become the mother tongue of a speech community.

   2. Creole has a community of native speakers i.e. it is formed from expanded pidgin which become the mother tongue (native
   language of the new   generation) thus Creole belongs to a particular speech community who uses it as the native language.

2. Creole has a file range of function as any other language i.e. it is treated or regarded as a full language and performs all functions
   that any language can perform and hence used as the mother tongue of the vast majority of particular countries for example English
   lexified Jamaican used in Jamaica.
3. Creole has a comprehensive grammar with its grammatical rules embodied with precise syntactic systems than expanded pidgin i.e.
   the syntax (grammar) of  Creoles is obit more advance than that of pidgin.
4. Creole is a permanent language since it is transformed from expanded pidgin and exists in a particular geographical location or
   country and used permanently  by a speech community. In some countries creoles may even become the National language used
   officially in public places, codified in dictionaries etc.
5. Creole has comprehensive vocabulary which are derived from another dominant or lexifier language i.e. Creole have more developed
   vocabulary compared to pidgin.

                   (i)     International language

This is the language which has been worldwide accepted as a tool of communication among various Nations of the world. I.e. it is the language used or spoken in different Nations from different continents of the world such a language ought to be accepted by UNO as the major means of communication in the international forms.

At present it is only English and French which have been accepted as the most prevailing international language.

Criteria which make  language international

There are several factors to be considered in the promotion of a language to be international

(i)       The number of speakers that the language has in order for the language to become international, it needs to have a reasonable number of the native and non–native speakers. I.e. the language should either as a native language or a non- native language. For example English is said to have over 600,000,000 speakers from different countries but surprisingly Chinese has about 900,000,000 speakers but it is not on international language. This is because Chinese is only spoken by the native speakers within China.

(ii)         The number of countries and continents i.e. the extent to which the language is geographically dispersed.

In order for the language to be international. It ought to be used or spoken in different countries from different or various continents of the world. For example English is used as the first language in many countries such as UK< USA< Ireland, Australia, New-Zealand, Canada, the Caribbean countries and South Africa. It is also used as the second language in the common wealth countries such as Zimbabwe, Pakistan, Nigeria, India, Kenya etc the same applies for French in West African countries.

(iii)      The economics and political influence and power of the native speakers. I.e. how economically and politically the native speakers are influential. This implies that in order for the language to be international, its native speakers (the countries were that language is used as a native language) should have a great power and influence over other countries. For example the Americans and the British being political and economical influential may force English as their native language become international.

(iv)        The extent to which the language is the medium for science, literature and other important areas or aspects. This is also referred to the languages vehicular load. For the language to become international is should  be the medium (tool) for science and technology, literature and other aspects of human life such as culture, economics, politics etc. this implies that an international language needs to cater for several purposes or functions rather than being only for communication, it should go beyond communication.

(v)            Acceptability of the language by UNO

The international language ought to be worldwide accepted by UNO and the world educated linguists as the major means of communication in all international affairs in the world. The language needs to be standard, codified (written in Books) and used as one of the official language of UNO.

NB: With above criteria English and French qualify to be the international language

            (j) Lingua-Franca

This is a common language which is adapted in the malt-lingual society (the society with many languages) in which all the speakers are not proficient in all language being used or spoken. I.e. it is the language which had been accepted as the common means of communication in the community with different languages.

This is an auxiliary language that it used to facilitates routine (day- to- day) communication between people who have different linguistics backgrounds in that they have different language for example Swahili in Tanzania is a lingua- franca English is a lingua- franca of the world.

   (k)Diglossia

This is a situation whereby two language or language varieties coexist (exist side by side) in a community in which each language or language variety is used for a different purpose or social function.

In this situation one language or language variety has a higher status than another so one is considered to be high and the other as low.

A high variety language is used for formal or serious matters in the society such as in education official matter, public places, international affairs etc on the other hand, the low variety (language is used for informal uses or such as friendly letters, conversation.

The Diaglossic nature of language in Tanzania entails the existence of three language English, Swahili, Ethnic community language as Double overlapping Diaglossic due to the fact that one language(Swahili) is used in both formal and informal domains when compared with the vernacular language and English respectively.

This implies that when Swahili is placed with vernaculars. It is considered as a high language is considered as low. On the other hand when Swahili is placed with English, English is high where as Swahili is low.

   (l)Bilingualism

This is the ability of (the use by) of an individual of two languages (or more) i.e. it is the situation whereby an individual person has the ability to speak two (or more) languages.

A person with the ability of using or speaking two languages is technique known as a Bilingual person.

The following are the features of a Bilingual person:
1. Ability to use, speak or know two languages equally well or perfectly.

2. The ability to use or speak one language and understand another language without being able to speak or use it.

3. The ability to use each language in different types of situations or Domains for example at home, at school or at work.

4. The ability to read and write in any one of the two language

5. The ability to use each language for a different communicating purpose for example talking about personal life writing letter.

6. A Bilingual is the one who has learn two languages in the family.

7. A Bilingual is the one who has used two languages since childhood.

WHAT IS A LINGUIST?

Is a scholar who studies language scientifically i.e. is a person who is specialized in the scientific study of language (linguistics). A linguist is not necessary a speaker of the language he or she is studying for example he or she study the grammar of a certain language without being able to use of speak it.

 ENGLISH IN TANZANIA
 With the present sociology-linguistics situation in Tanzania, English language has acquired a certain status and role and hence in several domains as follows:-

1. English is used as the major international language Since Tanzania is among the countries in the world, it uses English in all international affairs to  communicate with people from other language as well as the international conferences and meeting.
2. English is used as the foreign language
   This is due to fact that English has been adapted in to be used in Tanzania from  another countries i.e. Britain, these came into being as a result of the  British  colonization of  Tanzania.
3. English is used as the medium of instruction from secondary school levels up to the university level I.e. the teaching and learning process is conducted by or through the use of   English language except during the teaching of Swahili and French.
4. .English language is used as one of the official languages together with Swahili i.e. the Tanzanian Government has declared both Swahili and English to be used in all official matters and public places.
5. .English language is used as one of the subjects at all levels of education from primary school to the university level.
6. .English language is in transition between enjoying the status of the foreign language and the second language i.e. there are situations whereby English is only used  as a foreign language and the other situation whereby the status of English is now changing into being the second language especially in urban areas were Swahili is used as the first language from being the second language.

SIGNIFICANCE OF LANGUAGE IN HUMAN SOCIETY

Language being the only medium of communication used by human beings has a great role or significance that it plays in human society as follows.

1. Language as a unifying and dividing factor.

Language is an important factor in the enforcing unity among the people i.e. it brings members of the society together as either a sole means of communication or as an element which inspires a sense of oneness or togetherness among the people of a respective society. This putting together of members of a society makes language a unifying factor.
For example Swahili has made Tanzania feel united due to the fact that Tanzanians use Swahili as there day to day language the same applies to English in UK and USA.
There are cases when language is said to be a dividing factor. This is when language does not put members of the community together. This happens especially in countries with multiplicity of languages i.e. the countries were many language with or of more or less the same demographic or social importance exist and each language users struggle for dominance of other languages in the country, hence conflict for example in Nigeria there are three languages Igbo, Hausa and Yoruba, in Benin Yoruba, Dogon and Ga. Rwanda/ Burundi – Hutu, Tutsi
In some countries, the foreign language have been adopted as their national languages, for example English in Sierra Leone, Liberia and Uganda, French in Senegal, Ivory Coast and DRC.

2. Language as a factor for cultural and National identity.
              In a society there are many elements that could identify a particular cultural entity such as dress, make ups, foods, taboos, particular manners
   etc.Nonetheless language is the most dominant element of culture which is more obvious and specific than elements, that is the culture of a
   particular community is easily identified through the language used by that community.
   However language is also an identity of the nationality of an individual since a speaker speaking a certain language can identify his country of
   origin, which means language among the ways that can identify nations in the world. For example if you are in a foreign state and you’re heard
   speaking Swahili, people will without doubt, judge you as a Tanzanian.
3. Language as a factor for social stratification

Language may play the role to faster, re-enforce or perpetuate differences in the society. I.e. it facilitates the social classes existing in the society. This is noted in the fact that the use of a certain language or language variety determines the social classes existing in the society determines the social class would tend to use a different variety of language. These can be identified in the use of certain words, choice of words, the command of language as well as the use of a certain accent (pronunciation)
Special stratification may involve educated Vs Non-educated, villagers Vs Urban dwellers, poor Vs rich, farmers Vs Workers

4. Language as a mirror of cultural and physical realities.

As a mirror it reflects an image, equally language reflects all the accumulated knowledge, customs, traditions and believes and other forms of experiences of a given social group. It also shows how people of a given community define the world surrounding them. Language therefore is the means by which cultural and physical experiences are accumulated, stored and transmitted from one generation to another. For example the use of certain word reflect the culture of the community using that word, such as Ugali reflect the bantu culture as used in Swahili.

5. Language as a factor social development

Language plays a very significant role in the promotion of social activities and services such as school, hospital, water supply, housing and transport etc. i.e. human beings used language to co-ordinate various activities.
Through language we also get information through mass media such as newspapers, radio and Television which in Euro accelerate social development.
Where a common language exist between leaders and masses, there is always a sense of closeness, understanding and belongings hence the leaders are easily implemented to promote social development i.e. when the policy makers communicate their policies to the policy implementers and the implementers put the policies in practice, in that way development is attained. Here language plays a great role because these policies are presented using language but for the countries were foreign language are adopted as National languages; there is always a big gap between leaders and the masses and these for a hindrance for social development.

6. Language as tool or medium of communication.

Language facilitates the transfer of information from one person or place to another. This is the central or most significant role of language since language is the medium through which human beings communicate their thoughts, ideas, opinions, experiences and expectations with language, human society is able to communicate in various ways and events in different form such as conversations, greetings, telephone, discussion, mass media instructions etc. all these ways use language for disseminating information.

THE STATUS OF ENGLISH IN THE WORLD AND IN TANZANIA

English has different status in different parts of the world and Tanzania as follows:-

1. English as an international language

English is an international language; the following are the factors which qualify English language to be international language.

• The number of speakers that a language has, here reference is made to the number of native and non-native speakers. English is said to have over 600 million speakers.
•         The extent to which language is geographically dispersed, there we look at the number of continents in which the language is used or needed. English is  spoken in almost  all parts of inhabited parts of the world for that reason English is used as the world’s lingua franca.
• The economics and political influence and power of the native speakers. I.e. how economically and politically the native speakers are influential. This implies that in order for the language to be international, its native speakers (the countries were that language is used as a native language) should have a great power and influence over other countries. For example the Americans and the British being political and economical influential may force English as their native language become international.

• The extent to which the language is the medium for science, literature and other important areas or aspects. This is also referred to the languages vehicular load. For the language to become international is should  be the medium (tool) for science and technology, literature and other aspects of human life such as culture, economics, politics etc. this implies that an international language needs to cater for several purposes or functions rather than being only for communication, it should go beyond communication.
• Acceptability of the language by UNO

The international language ought to be worldwide accepted by UNO and the world educated linguists as the major means of communication in all international affairs in  the world. The language needs to be standard, codified (written in Books) and used as one of the official language of UNO.

NB: With above criteria English and French qualify to be the international language

2. English as a native language

By native language we mean the first language. It is the language which people acquire first before they are exposed to any other language. English is used as a native language in Britain, U.S.A, Australia, New Zealand, Canada, South Africa and the Caribbean. In countries such as Kenya and Zimbabwe there are few people who speak English as their first language.

3.   English as a second language.

A Second language refers to a language which is not one’s first language but is necessary for certain official, educational or commercial activities.
English is a second language in most common wealth countries like Pakistan, India, Nigeria, Kenya, Malawi, Zambia and other countries. It should be noted here that a second language is defined by use so a second language differ from a foreign language in that a second language is more useful in a place than a foreign language in Tanzania for example French is a foreign because its use is very limited.

4. English as foreign language

A foreign language is used to mean a language that is used by the same one across the countries such as to communicate with foreigners reading books and newspaper commerce and travel. In short the use of a language as a foreign one is very restricted in Rwanda, DRC, Burundi, Japan, and China. English is used as foreign language.

5. English as a national language

A national language is one which is considered to be the mainly of a nation and which is officially declared so. E.g. Swahili is the national language in Tanzania.
English is a national language in many common wealth countries such as Nigeria and Zimbabwe.
In countries where there many languages of national status the term OFFICIAL LANGUAGE is prepared. Example Canada where there is English and French.

THE CONCEPT OF CYTOLOGY.

Cytology is the study of cells, their structures, functions, characteristics and adaptations.

THE CELL THEORY

The bodies of all living things are made up of cells.

Robert Hooke (1665) was the first person to discover a cell from a plant cork. The cells looked like boxes. Other people who studied the structure of cells are Lamark (1809), Detrochet (1824) and Turpin (1826).

Schleiden (1838) studied the plant cells and emphasized that the cells are organisms and entire animals and plants are aggregations of these organisms arranged according to the definite laws.

In 1839 Schwann, a German botanist stated that ” we have seen that all organisms are composed of essentially like parts namely of cells”.

IMPORTANCE OF CYTOLOGY

Cytology has been very important discipline in the research diagnosis and treatment of human diseases. Most of health problems people encounter involve the cell disturbances.

The study examines cell interaction. Studying how cells interact or relate to other cells or environments the cytologists can predict problems or examine the dangers to the cell and identity type of infections.

THE MAIN IDEAS OF THE CELL THEORY

1. All organisms are made up of cells.
2. The new cells are derived from the pre-existing cells by the process of cell division (mitotic and meiotic division).
3. All chemical reactions/metabolic activities in the bodies of the organisms take place within the cells.
4. The cells contain hereditary materials which are passed from one generation to another.
5. Given a suitable condition, a cell is capable of independent existence.

CHALLENGES OF THE CELL THEORY

 Hereditary materials are also found in viruses, mitochondria and chloroplasts, all of which are not viruses.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

STRUCTURE OF CELLS AND FUNCTIONS

The five structures are also known as ultra structure and are obtained by two techniques.

 Physiological or metabolic activities take place within a cell. Viruses though are not cells, have life within their hosts.

 The new cells arise from pre-existing cells by cell division. In this postulate the theory does not specify about the origin of the first cell.

 All living things must have cells. This postulate is challenged by the existence of viruses, where when they are inside the body of their host, viruses act as living things even though they don’t have cellular organization.

 Electronic microscope.

 Cell fractionation.

A cell is usually a tiny, three dimensional sac of many organelles which are suspended within an aqueous medium (the cytoplasm) containing or contained (bounded) by a cell membrane.

In the case of plants, a cell wall is bounded by a cellulose cell wall.

The bulk of these structures (organelles) of the cells is referred to as a cytoplasm.

Cytocil is the fluid part of the cytoplasm.

PROKARYOTIC CELLS.

They are extremely small for example bacteria all range from 0.5 – 10 micrometers.

They appeared about 350 million years ago.

Cells of prokaryotes lack the true nuclei that are their genetic material (DNA) are not enclosed by the nuclear membrane and lies freely in the cytoplasm.

EUKARYOTIC CELLS

The cells of eukaryotic have three basic parts

1. The plasma membrane.
2. The cytoplasm.
3. The nucleus.

Plasma membrane. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

This is also called the cell surface membrane as plasma membrane or plasma lemma which separates the contents of the cells from the external environment, controlling the exchange of materials.

In animal cells it is an outermost layer where as in plant cells it is beneath the cell wall. E.g. neurillema in neurons.

Muscle cells – sacrolemma.

STRUCTURE OF THE CELL MEMBRANE

There are two models suggested by different scientist to try to describe the cell membranes.

These are;

1. Daniel-Davson model (1935)
2. Fluid mosaic model (1972)

Daniel-Davson model

Diagram 1

According to Daniel and Davson, the membrane is structurally composed of two chemical substances that form their own layer.

1. Protein layer made up of molecules. The layer is continuous and lacks pores.
2. Phospholipids (at least two layers of phospholipids) oriented with their polar (hydrophilic ends near the surface and their non polar (hydrophobic) hydrocarbon chains in the interior of the membrane as far as possible from the surrounding water. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

According to the model, the membrane is structurally rigid static and non dynamic.

Strength of the model.

1. The model suggests that the membrane is composed of proteins and lipids.
2. Ampliphetic (double) nature of phospholipids such as phospholipids molecule has a polar head (hydrophilic) and a non polar tail (hydrophobic).

WEAKNESS OF THE MODEL

1. The model suggests that the protein layer is continuous. Researches done by scientists show that the protein layer is in-continuous.
2. The membrane is static is a wrong concept since the membrane is a dynamic ever changing structure.
3. Lack of pores in protein layers.

The protein molecules in a membrane have pores for passage of materials.

4. The model does not indicate the presence of a carbohydrate.

THE FLUID MOSAIC MODEL.

The model was put forward by singer and Nicolson 1972 in order to modify the Daniel and Davson model.

According to the fluid mosaic model, the membrane is an ever-changing structure in which the mosaic protein floats on the lipid bilayer acting as a fluid.

Proteins in this model do not form a continuous layer covering both sides of the membrane as proposed by Daniel and Davson model.

According to this model, the membrane has 3 constituents.

 Lipids (45%)

 Proteins (45%)

 Carbohydrates (10%)

1. Lipids.

There are two types of lipids. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Glycolipids;

These are lipids associated with short carbohydrates chain.

ROLES OF GLYCOLIPIDS

Cell to cell recognition.

Act as receptors for chemical stimuli.

1. Phospholipids;

These are lipids associated with phosphates. They form 2 layers i.e. phospholipids bilayer. Each phospholipid consists of a polar head (hydrophilic) and a non polar tail (hydrophobic). Act as a fluid and move about rapidly in their own layer. Since phospholipids are constantly in motion, the membrane is described as being fluidly.

ROLES OF PHOSPHOLIPIDS

1. Form the basic structure of the membrane.
2. Determine the fluidity of the membrane.
3. Allow the passage of fat soluble substances.

NB: cholesterol is a type of steroid located in between phospholipids keeping them fluidly.

ROLES OF CHOLESTEROL

1. Disturb the close package of phospholipids keeping them fluids.
2. Increase the flexibility of the membranes by allowing relative movements of the bilayers without actual displacement because it acts as an unsaturated fatty acid lubricating bilayer.
3. PROTEINS

These exist as globular in the membrane, i.e. they never form a continuous layer.

Within protein molecules or between adjacent there are poles. These may either be hydrophobic or hydrophilic.

Since the phospholipids are always in constant motion (fluid) proteins float in it forming a fluid mosaic model. The proteins are organized in a particular pattern known as mosaic. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

There are protein molecules that extend/ transverse both layers of membranes. Other proteins are partially embedded in the membrane. These are called intrinsic proteins.

Some proteins float freely inside the membrane, hence they are called peripheral or extrinsic proteins.

TYPES AND ROLES OF PROTEINS.

1. Carrier proteins or channel proteins.

These are involved in the selective transportation of polar molecules. i.e. ions across the membrane e.g. movement of glucose to the cell, chlorine ions. (Cl-)

2. Enzymes

Catalyze different metabolic reactions.

3. Receptor molecule.

Some act as receptors for chemical stimuli example hormones.

4. Antigen.

Identity markers. These are glycoprotein. They have different shapes in every kind of a cell. They have specific side chains thus are recognized by other cells and behave in an organized manner.

5. 5. Energy transfer. In some physiological processes such as photosynthesis and respiration, some proteins are involved in energy transfer (special form of membrane found in chloroplasts and mitochondria).
6. CARBOHYDRATES These branches to the outside of the membrane as an antennae or feelers. There are two types;
7. Glycoprotein ( carbohydrate chain – plus protein)
8. Glycolipids ( carbohydrate chain plus lipid)

They form a layer of glycocalyx

ROLES

1. Cell to cell recognition (in making tissues since same cells combine so similar cells will have similar glycolipids/ glycoprotein).
2. To receive chemical stimuli.

STRENGTH OF FLUID MOSAIC MODEL.

1. It realizes the presence of phospholipids bilayer and protein layer.
2. The presence of polar head (hydrophilic) and non polar tail (hydrophobic) in the phospholipids.
3. It shows that the membrane is not static.
4. It shows the presence of carbohydrates.
5. It shows that the protein layer is not continuous.
6. It indicates the presence of pores in the membrane passage of materials.

Diagram 2

FUNCTIONS OF CELL MEMBRANES.

1. It protects the cytoplasm contents of the cells.
2. It allows passage of materials in and out of the cells since it has pores.
3. In some membranes e.g. those of the intestine cells, there are microvilli which increase the surface area for absorption of materials.
4. Acts as receptor sites for chemical stimuli such as hormones.

5. In nerve cells, the membrane is over lined with a fatty sheath (myelin sheath) which prevents the spreading of local currents to other neurons.
6. It aids cell to cell recognition when membranes of two cells come together.

VARIOUS WAYS BY WHICH MATERIALS PASS THROUGH THE MEMBRANES.

1. Permeability

The plasma membrane is a thin elastic membrane around the cell which usually allows the movement of small ions and molecules of various substances through it. This nature of plasma membrane is termed as permeability.

2. Osmosis

The plasma membrane is permeable to water molecules. To and fro movement of water molecules through the plasma membrane occurs due to the difference in concentration of the solutes on its either side. The process by which the water molecules pass through a membrane from region of higher water concentration to a region of lower water concentration is termed as osmosis.

3. Diffusion or passive transport.

The diffusion of a certain solute or substance takes place through the plasma membrane depends on the concentration and electrochemical gradient.

4. Active transport.

When molecules or ions move through the plasma membrane from low concentration to higher concentration, they require energy for such movement.

The energy is provided by ATP which is produced by the mitochondria.

Through the pores of plasma membrane some chemicals such as urea and glycerol could pass. It has been shown that large molecules of certain proteins also penetrate the cell.

5. Endocytosis and exocytosis.

The plasma membrane particles actively in the ingestion of certain large sized foreign or food substances.

The process by which the foreign substances are taken and digested is known as endocytosis. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

In the process of exocytosis, the cells which have secretory functions such as pancreatic cells pass out their enzyme secretions outside the cell.

According to the nature of the food of foreign substance, endocytosis may be classified into two types;

1. Pinocytosis

When the ingestion of food materials in bulk takes place by the cell through the process known as pinocytosis. 2. Phagocytosis Sometimes the large sized solid food or foreign particles are taken in by the cell through the plasma membrane. The process of ingestion of large sized solid substances by the cell is known as phagocytosis. Question: what is the significance of a fluid mosaic model in the plasma membrane? Ans:

 It explains easily the known physical and chemical properties of the membrane.

 It is the starting point to understanding the fix of the cell.

o All membranes of the cell plus the tonoplast and those of the organelles have the fluid mosaic construction.

NB: this point provides the clues about the distribution of cell membrane in the cell and its organelles.

NOTE:

Where

R = rate of transport of material. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

A = cross section surface area.

CYTOPLASM

This is the part of a cell, which is filled with fluid in the protoplasm. This part of the cell is the ground substance of the cell known as the hyaloplasm, where the cell organelles are suspended. Cytosil is the soluble part of the cytoplasm.

Cytoplasm is distinguished into the following structures

1. Cytoplasm matrix

The space between plasma membrane and nucleus is followed by a morphous, translucent, homogenous liquid known as cytoplasm matrix and hyaloplasm.

The cytoplasm matrix consists of various inorganic compounds e.g. carbohydrates, lipids, proteins, nucleon proteins, nucleic acids (RNA and DNA) and variety of enzymes.

The peripheral layer of a cytoplasm matrix is relatively non-glandular viscous and known as endoplasm.

2. Cytoplasm inclusion

The cytoplasm matrix contains many refractive granules of various sizes; these granules in the animal cells are known as cytoplasm inclusion.

The cytoplasm inclusion includes oil drops, yolk granules, pigments, secretory granules and glycogen granules.

Such granules in plant cells are known as plastids. The most common plastids are the chloroplasts (containing pigment chlorophyll), the leucoplastids (white color plastids) ,omyplastids ( the plastids that store starch) and lipoplastids ( which contain fats).

NB: plastids like cytoplasmic inclusion having only storage functions but also perform various important synthesis and metabolic activities such as the production of food materials due to the presence of chloroplasts.

ANIMAL CELL STRUCTURES

Diagram of the animal cells under light and electron microscope.

DIAGRAM 3

DIAGRAM OF ANIMAL CELL UNDER ELECTRON MICROSCOPE MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

DIAGRAM 4

ANIMAL CELL STRUCTURES

Characteristics;

1. Have irregular shape.
2. Have centrioles.
3. Have lysosomes.
4. Lack cell walls.
5. Lack plastids.
6. Store carbohydrates in the form of glycogen e.g. phagocytotic vacuoles, pinocytotic vacuoles, autophagic vacuoles and etc.
7. Cytokinesis occurs by furrowing i.e. periphery – centres direction of constriction of cell membrane.

STRUCTURE OF THE PLANT CELL

A plant cell is incased in a tough and rigid cellulose cell wall.

Beneath the cell wall is the cell surface membrane which surrounds the cytoplasm.

The latter contains organelles; the prominent being vacuole plastids e.g. chloroplasts and nucleus. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

-Since a greater part of the cell is occupied by the vacuole, then the cytoplasm and nucleus are squeezed by the vacuole to the periphery.

-When viewed under light microscope; only a few structures are seen under high magnification power, even finer details are seen.

Diagram 5

Diagram of a plant cell under light microscope MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

DIAGRAM 6

CHARACTERISTICS OF PLANT CELLS

1. It has a fixed shape.
2. It has a cell wall made up of cellulose.
3. It has large permanent vacuole,
4. It has plastids; chloroplasts, chromoplast and leucoplasts.
5. Stores carbohydrates in the form of starch.
6. Lack lysosomes.
7. Lack centrioles.
8. Cell division; cytokinesis follows cento-periphery direction.

Similarities between a plant and an animal cell:

Both Have;

1. Plasma membrane
2. Distinct nucleus
3. Ribosome
4. Endoplasmic reticulum
5. Cytoplasm
6. Golgi apparatus
7. Qn What is an organelle?

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

An organelle is a distinct part of a cell which has a particular structure and function e.g. Mitochondria, chloroplast, ER etc.

CELL WALL

Cell wall is the structure that occurs externally to the cell.

Organisms with cell wall include.

8. Bacteria – have cell wall made up of murein and peptidoglycogen.
9. Fungi – has cell wall made up of chitin.
10. Algae and plant have cell wall made up of cellulose.

Plant cells cell walls.

It is the structure external to the cell; it isn’t an organelle although it is a product of various cell organelle e.g. microtubules and Golgi apparatus.

CHEMICAL COMPOSITION.

It is made up of cellulose (mainly fibres) forming amorphous matrix of the cellulose that surrounds the entire cell.

Such fibre is made up of several hundred microfibrils which form the network of cell wall.

In addition to cellulose plant cell wall consists of pectron and hemicellulose which contribute to mechanical strength of the organism.

Pectron

These are polysaccharides of galactose and galactronic acid. Pectron may combine with Ca2+ or Mg2+ to form calcium pectate or magnesium pectrate, which are important components of the first layer of cell wall to be laid down on middle lamella.

Hemicellulose MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Hemicellulose is the mixture of many compounds, but the chief ones are sugar e.g. glucose and sugar acid residue.

Hemicelluloses which form hydrogen bounds with cellulose fibres in the cell matrix. The cell wall is usually modified by deposition of other substances such as alginic acid and calcium carbonate in the case of algae.

Functions of cell wall.

1. Mechanical support and skeletal support of individual cell and plants as well. This is through lignifications.
2. To prevent cell from bursting in hypotonic solution.
3. Control cell growth and shape. Orientation of cellulose microfibrils limits and helps to control cell growth and shape because of the cells ability to stretch is determined by their arrangements.
4. Movement of water and material salts.

The system of interconnected cell walls (apoplast) is a major pathway of the movement of water and dissolved mineral salts.

The cell walls are held together by middle lamellae, they also posses minute pores through which structures called plasmodesmata form living connections between cells and allows the protoplast to be linked in a system called symplast.

5. Reduction of water loss and reduced risk of infection (due to its waxy cuticle).
6. Transportation of materials. The walls of xylem vessels and sieve tubes are adopted for long transportation of materials through the cells.
7. Barrier to water movement.

The cell walls of root endodermal cells are impregnated with suberin that forms a barrier to water movement.

8. Some cell walls are modified as food reserves as in the storage hemicelluloses in some seeds.
9. Transport of materials by active transport.

The cell wall of transfer cells develops an increased surface area and this increases the efficiency and transfer materials by active transport.

CELL ORGANELLES OR ORGANOIDS. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Besides the cellular inclusion and plastids, the cytoplasm matrix contains many large sized structures known as cell organelles or organoids which perform various important synthesis, transportation, support and

reproduction.

These organelles are the endoplasmic reticulum, ribosome, Golgi complex, liposomes, mitochondria, plastids, centrioles, cilia etc.

Functions of cytoplasm

1. It provides medium for chemical reaction to take place like protein synthesis, lipids synthesis and etc.
2. It stores useful materials such as amino acids, proteins, starch, carbohydrates, lipids, O2 etc.
3. It stores waste materials such as C02 and nitrogen waste etc.
4. It controls the absorption of materials across the membrane due to its concentration gradient.

CELL ORGANELLES

1. ENDOPLASMIC RETICULUM

Is the cytoplasm matrix, is transverse by a vast reticulum or network at interconnecting tubules and vesicles which is known as endoplasmic reticulum or ER.

The endoplasmic is having a single vast and interconnected cavity which remains bounded by a single membrane. The membrane of endoplasmic reticulum is supposed to be originated in pushings of plasma membrane

in the hyloplasm (matrix) because chemically it consists of a lipoproteinous structure like plasma membrane.

The membrane of the endoplasmic reticulum may be either smooth when they do not have attached ribosome and rough when they have the attached ribosome.

The membranes of endoplasmic reticulum are found to be continuous with the nuclear membrane and plasma membrane.

FUNCTIONS OF ENDOPLASMIC RETICULUM MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Transport of materials from exterior to the nucleus or to cytoplasm organelles such as Golgi complex.
2. It provides mechanical support to the cytoplasm matrix.
3. Functions as a cytoplasm framework.

Surfaces for some of the biological activities of the cell catalyst its complex folding provide an enormous surface for such activities.

4. Synthesis and transfer of lipids.( smooth endoplasmic reticulum)
5. In the liver the smooth endoplasmic reticulum detoxifies many poisons and drugs.
6. The rough endoplasmic reticulum transports proteins synthesized in the ribosome of the rough endoplasmic reticulum.
7. Formation of Golgi bodies as they are modified endoplasmic reticulum.
8. Routes for movement of materials from the nucleus to the cytoplasm.

DIAGRAM 7

2. GOLGI APPARATUS/ DICTYLOSOMES This cell organelle is also known as the Golgi body, Golgi complex or sityasome. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

DIAGRAM 8

It is the apparatus which consists of membranous sacs called cisternae and a system of small vesicle (called Golgi vesicles or dictysome vesicles) and vacuoles of various sizes.

The membranes of Golgi complex are of lipoproteins and these are supposed to be originated from the membrane of endoplasmic reticulum.

FUNCTIONS

1. Produce secretions

There are many Golgi apparatus in;

 Cells of salivary gland

 Cells of root cap

 Cells of endocrine glands i.e. pancreas

2. Modification of materials.

The combination of carbohydrates and proteins to form glycoprotein takes place in them. Many materials such as mucin are glycoprotein. It takes place in the cistern.

Carbohydrate chain + lipids = glycolipids

3. Production of carbohydrates example cellulose produced in plants after division. Thus this separates one cell from another. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

4. Transport of lipids (storage and transport of proteins and lipids) after digestion, the fatty acids and glycerol are formed. In the endoplasmic reticulum fatty acids and glycerol unite to form lipids (triglycerides). The latter are passed to the Golgi apparatus where it transports them to the plasma membrane as lymphatic system and going to the lymphatic system.
5. Formation of lysosomes.
6. Synthesis of various types of carbohydrates from simple sugars.
7. It activates the mitochondria to produce ATP.
8. It forms the acrosome of the sperms.
9. LYSOSOMES.

These are spherical single membrane bound organelles containing digestive enzymes.

-lipase

-carbohydrases

– Nucleases

The enzymes are synthesized in ribosome RER transported to the Golgi apparatus for modification. The Golgi vesicles are detached from the Golgi apparatus and remain in the cytoplasm as lysosomes because they contain digestive enzymes.

FUNCTIONS

1. Functions as storage vesicle for many powerful digestive (hydrocytic) enzymes.
2. Acts as digestive system of the cell enabling it to process some of the bulk materials taken in by phagocytosis or pinocytosis. Digests parts of the cell such as worn out organelles and also to digest the stored food contents of chloroplast A and B in extracellular digestion.
3. Play role in some developmental process e.g. remolding of bones and fractures.

NB: in plant cells, the large contrast vacuole may act as lysosomes although bodies similar to lysosomes of an animal cell sometimes seen in the cytoplasm of a plant cell. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

4. RIBOSOMES.

Structurally it has two sub-units, i.e. small subunit and large subunit.

Each of the two subunits is composed of rRNA (ribosomal RNA) and proteins.

It is present in both eukaryotic and prokaryotic cells. The sizes can be determined by the sedimentation when centrifuging showing the 80’s and 70’s ribosome.

-80’s ribosome are present in R.E (rough endoplasmic) reticulum of eukaryotic cells.

-70’s ribosomes are present in prokaryotes as well as mitochondria and chloroplasts of eukaryotic cells.

FUNCTIONS OF RIBOSOMES

1. They provide large surface area for protein synthesis.
2. They are binding sites of the RNA.

ADAPTATIONS OF RIBOSOMES.

The ribosomes are the sites for protein synthesis. it has the following characteristics.

1. Presence of enzymes capable of catalyzing the synthesis of peptide bonds.
2. Presence of ribosomal RNA (rRNA) that attract other types of RNA i.e. mRNA and tRNA towards the ribosome’s.

5. VACUOLES
6. A vacuole is a fluid filled sac which is bound by a single membrane.

In animal cells, there are relatively small and temporary vacuoles such as phagocytotic, pinocytotic, autophagic vacuoles in plant cells; the vacuole is large and occupies a greater proportion of the cytoplasm.

The membrane bounding the vacuole is the tonoplast and the fluid inside is the cell sap or vacuole sap. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

The cell sap is a mixture of many substances; concentrates solutions of sugar, salt, organic acids, gases such as C02 and oxygen, pigments and waste products of metabolism.

It also contains enzymes similar to those of lysosomes.

ROLES OF CELL VACUOLES

1. They are involved in primary plant growth. It is a result of turgor pressure generated inside the vacuoles as a result of entry of water. This causes cell expansion as the tonoplast is pressed against the cell wall.
2. The pigment contained in the cell sap is responsible for flower color and therefore play a key role to pollination.
3. They contain enzymes similar to those of lysosomes when plant cell dies. The tonoplast looses the differential permeability and enzymes escape causing autolysis.
4. Vacuole acts as a temporary store of waste products such as crystals of waste calcium oxalate, toxins and metabolic waste products of plants.
5. The vacuoles sometimes functions as food reserves e.g. sucrose mineral salts and insulin are stored in vacuoles.
6. In prokaryotes it serves for buoyancy.
7. MITOCHONDRIA

Structure of mitochondria

It is a sausage shaped or an oval shaped organelle surrounded by a double membrane (mitochondrial envelope). The envelope consists of the outer and inner membrane.

Between the two membranes there is a space, the intermembranal space.

The outer membrane is smooth while the inner membrane is coiled to form t=surface area for attachment of membranes.

The ground substance of the mitochondrion is called matrix. This contains

1. Several enzymes responsible for Krebs cycle.
2. Circular DNA that resembles that of prokaryotic cells. It is for self replication of mitochondria.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

3. 70s ribosome like those of prokaryotic cells. These are for protein synthesis e.g. enzymes

Diagram of mitochondrion 9

Functions of mitochondrion

The main function of mitochondrion is to yield energy during respiration.

About 98% of energy is synthesized e.g. one molecules of glucose yield 38 ATP. Out of 38ATP 36 is synthesized in the mitochondrion by the reactions of Krebs cycle and electron transport chain. Thus it is called power house or POWER station or power plant of the cell.

Adaptations of the mitochondrion to energy productio

1. Presence of outer membrane and inner membrane to allow entry and exit of materials.
2. The inner membrane is coiled to increase the surface area for attachment of enzymes responsible for electron transfer.
3. Presence of matrix which is as granular and gives enough space for reaction to take place (Krebs cycle reaction) also matrix contains Krebs cycle enzymes.
4. Presence of circular DNA for replication of the mitochondrion.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

5. Have 70s ribosome’s for synthesis of proteins.
6. Presence of phosphate for production of ATP.
7. Presence of Oxysome and water accompany aerobic respiration.

NB: the inner folded to form partitions called cristae which enables different types of metabolic activities to take place. This phenomenon is called compartmentalization hence enables multi-enzymes systems to operate.

ENDOSYMBIOTIC THEORY

(Evolution of mitochondria)

The mitochondria were originally independent prokaryotic bacteria like organisms which entered hosts cells and develop mutual relationship (symbiosis).

MITOCHONDRIA AS PROKARYOTIC CELL

1. Posses its own DNA and is able of self replication / reproduction.
2. Have a circular like bacteria DNA.
3. It is sensitive to different antibiotics such as chlorophyll and streptomycin which inhibit mitochondrial activities.
4. It contains ribosomes similar to those of bacteria.

7. 7. PLASTIDS These are organelles with double membrane, located in plant cells and algae

Types

1. Chromoplasts
2. Leucoplasts
3. Chloroplasts
4. CHROMOPLASTS

(Chromo – color / pigment)

These are types of plastids bearing pigments i.e. yellow, red, orange, purple pigments.

Found in MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Flowers
2. Fruits
3. Seeds
4. Leaves
5. Roots of carrots.

2. LEUCOPLAST (embryos and germ cells)

Leuco- colour / white.

These are colour plastids found mainly in storage organs. There are various types of leucoplasts;

1. Amyloplasts- contain starch
2. Lipoplasts – stores lipids
3. Proteoplasts- stores proteins

Structure of chloroplasts

The chloroplast

-the chloroplast is an oval shaped green in color due to presence of chlorophyll.

– It has two membranes an outer and an inner membrane which constitutes the double membrane or chloroplast envelope.

-Between the membranes there is the inter membrane space.

– The ground substance of the chloroplast is the stroma.

– The latter has a system of parallel running membranes called thylakoids.

-the interval between one grannum and the other is called intergranal lamellae.

– The stroma contains circular DNA and fewer small 70’s ribosomes and starch granules.

Functions of chloroplasts

1. It is the site of photosynthesis.

This is the process whereby green plants manufacture food from CO2 and water in the presence of light energy, it stores starch temporarily. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

2. The thylakoids have chlorophyll pigment for trapping sunlight energy.
3. It has grana and thylakoids to hold the chlorophyll in proper position for maximum absorption of light energy.
4. Stroma contains enzymes for dark reactions of photosynthesis.
5. Presence of phosphate which acts as a source of phosphate during phosphorylation.
6. Ribosomes and circular DNA for synthesis of proteins such as enzymes

Endosymbiotic nature of chloroplasts and mitochondria.

The chloroplast and the mitochondria are endosymbiotic structures within a cell. They are capable of leading life within a cell because;

1. They have double membrane which allows passage of materials in and out of their inside.
2. They have their own hereditary materials i.e. circular DNA. They are capable of self replicating.
3. They have ribosomes (70’s) thus synthesize proteins. E.g. enzymes.
4. Have matrix or stroma, the ground substance where various reactions take place.

STROMA; various photosynthetic membrane are found where light reactions take place and dark reactions in the aqueous part.

MATRIX: Krebs cycle of respiration.

5. They have their own enzyme system.

Therefore chloroplasts and mitochondria are said to be cells within cells.

The endosymbiotic nature of chloroplasts and mitochondria can be described as serial endosymbiotic theory (SET).

SERIAL ENDOSYMBIOTIC THEORY.

This theory accounts for the evolution of eukaryotic cells from prokaryotic cells.

Evidence / similarities of organelle and prokaryotic cells

 Double membrane as cell membrane.

 Circular DNA.

 70’s ribosomes.

 System of enzymes.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

SERIAL ENDOSYMBIOTIC THEORY.

It was suggested that mitochondrion, chloroplasts are descendants of ancient prokaryotic organisms.

-Eukaryotic cells arose from invasion of one large cell by other prokaryotic cells.

The SET states that;

“All eukaryotic cells contain genetic material (DNA) ribosomes that resemble those of prokaryotic cells’’.

-It suggests that prokaryotic heterotropes ingested other mitochondrion like prokaryotic and roughly at the same time began forming an organized nucleus.

Subsequently, non motile cells established a symbiotic relationship with yet another prokaryote in the form of spirochetes or spiroplasma bacterium, attached to the outside of the cell. Such as bacterium has a function like flagellum.

Eventually a photosynthetic prokaryote engulfed by this regardless as a primitive plant cell.

QNS

1. Chloroplasts, mitochondria and bacteria have features in common. Enumerate the features to reveal the truth of this statement.
2. Where in the body would you expect to find large number of mitochondria? Give reasons.
3. If mitochondria were to perform the function of the function of the chloroplast, what modification would it require.

8. MICROBODIES OR PEROXISOMES

These are small spherical bodies with 0.5 – 1.5 micrometers in diameter. The ground substance of a micro body contains important enzymes especially catalyze or peroxidase.

These enzymes catalyse the hydrolysis of hydrogen peroxide in water and oxygen.

These peroxisomes are found in liver, potatoes, pea seeds and bean seeds. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Diagram 10

FUNCTIONS OF PEROXISOMES

1. To break down the poisonous hydrogen peroxide to water and oxygen in the presence of peroxidase enzyme/ catalase.
2. In plants special peroxisomes called glycoxisomes are centre’s for glycoxylate cycle i.e. conversion of fats into carbohydrates especially during germination.

3.The leaf of peroxisomes are centers of photorespiration, especially in C3 plants e.g. beach plants, potato plant, tomato, coffee in cold areas.

CYTOSKELETON

This is a complex network of fibrous protein structure that exists in cytoplasm of eukaryotic cell and anchor proteins or organelles such as nucleus to their fixed location.

The structures which constitute cytoskeleton include;

1. Microfilament( actin filaments)
2. Intermediate filaments
3. Microtubules

1. MICROFILAMENTS(ACTIN FILAMENTS)

These are thread like structures arranged in sheets or bundles first beneath the cell surface membrane. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Diagram 11

-Chemically they contain actin and myosin.

-Each fibre is composed of two chains of protein loosely twisted about one another in helical manner. These proteins molecules can be assembled and dis-assembled.

FUNCTIONS

 Interactions of these fibres with myosin help in muscle contraction.

 Determine the shape of cell’s skeleton.

 Responsible for movement of materials within the cells.

 Cleavage of animal cells is brought about by the constriction of a ring of microfilaments after nuclear division, cytokinesis.

2. INTERMEDIATE FILAMENTS. These are structures intermediate between microtubule and microfilament (rope like microtubule of polypeptides)

Skin cells for example form intermediate filaments from proteins called KERATIN. When the skin dies the intermediate filament of the cytoskeleton persists. Hair and nails are formed this way. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

FUNCTION

1. Provide cells shape
2. Act as intercellular tendons preventing excessive stretching of cells.
3. MICROTUBULES

Microtubules are tubular structures made up of helizelly arranged globular subunit called tubulin.

-They are about 25 nm in diameter. Each has a chain of proteins wrapped round and round in a tight spiral. Large microtubules are found in cilia, flagella, centrioles (formation of spindle- fibres microtubules).

Functions

1. They bring about movement of chromosomes during metaphase in nuclear division.
2. Since they are tubular, they transport materials from one part of the cytoplasm to another, i.e. they are cytoconductors.
3. In cilia and flagella, they help in rhythmical beating up movement.
4. They determine the shape of the cell. (Skeletal support).

9. CILLIA AND FLAGELLA.

The cells of many unicellular organisms and ciliated epithelium of multi-cellular organisms consists of some hair like cytoplasm projections outside the surface of the cell.

-These are known as cilia or flagella and they help in locomotion of the cells. The cilia and flagella are made up of proteins adenosine triphosphate (ATP).

-In prokaryotic cells, cilia and flagella (If they have structure lacking 9+2 arrangement of microtubules and arise from basal bodies).

-In eukaryotic cilia and flagella are complex. They have the 9+2 arrangement of microtubule and arise from basal bodies.

10. CENTRIOLES.

Centrioles are present in animal cells only.

-They are two placed at right angle to each other.

-A number of rays called ultra rays usually surround the centrosomes. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Each centriole is composed of nine paired thin threads and is in the form of cylinder.

They aid in cell division.

11. PINOCYTOTIC VESSICLE

These are organelle formed as a result of in folding of plasma membranes as it takes large particles of food from outside the cell.

The process is called pinocytosis.

Eventually pinch off and form very small vacuole (vesicle).

FUNCTIONS

Transport large particles into the cell.

12. NUCLEUS.

-Nucleus is the functional unit of a cell.

It contains materials which control different activities within the cell; the genetic materials.

STRUCTURE OF THE NUCLEUS.

The nucleus has a membrane called nuclear membrane envelope.

Then nuclear membrane has some pores which allow some materials to pass in and out of nucleoplasm to allow communication on with cytoplasm called nuclear pores.

-Nuclear pores are made up of non-membrane materials forming nuclear pores.

-Nuclear envelope is semi permeable membrane allowing some materials to pass and others not to pass.

-The space inside the nucleus is filled by fluid materials which are called nucleoplasm. These are semisolid granules ground substance or matrix.

Within the nucleoplasm there are two components; MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Nucleolus
2. Chromatin
3. Matrix (aqueous)

Chromatin threads

Chromatin threads are grainy network of strands that undergo cooling into rod-like structures called chromatin.

Chemically chromatin and therefore chromosomes contains DNA (deoxyribose nucleic acids) and much protein and some RNA (ribonucleic acids) and few minerals.

Nucleolus

These are small dark regions where different RNA type examples ribosomal RNA is produced and RNA joins the protein to form the subunit of ribosomes.

-It synthesizes the ribosomes protein and is used in controlling the cell division.

Functions of nucleolus

1. Controls all metabolic activities of the cells
2. It regulates cell division.
3. Concerned with transmission of hereditary traits from parent to offspring.
4. Synthesizes and stores proteins.

PROKARYOTIC CELL

1. A WELL LABELLED DIAGRAM OF A BACTERIAL CELL.

DIAGRAM 12 MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

PROKARYOTIC CELL e.g. bacteria, cyano bacteria.	EUKARYOTIC CELL e.g. protoctista, green plants, animal and fungi.
1. Usually extremely small cells.	Usually large cells about 10-100 micrometer
2. Nucleus absent, naked circular DNA	Distinct nuclear region DNA helical shaped enclosed in a protein coat.
3. No nucleus.	Nucleus present
4. Few organelles and non are surrounded by an envelope (double membrane).	Many organelles envelope(bound) organelles ( i.e. double membrane bound organelles)
5. Internal membrane if present usually associated with respiration or photosynthesis.	Great diversity of internal membrane organelle e.g. Golgi apparatus, lysosomes, ER.
6.Flagella are simple lacking arrangement of microtubule.	Complex flagella with ( 9+2) arrangement of microtubule.
7. Have mesosome for respiration.	Use mitochondria for respiration
8. Some are nitrogen fixing.	No ability to fix nitrogen.
9. 70’s ribosomes.	80’s ribosomes

 

THE CONCEPT OF CYTOLOGY.

Cytology is the study of cells, their structures, functions, characteristics and adaptations.

THE CELL THEORY

The bodies of all living things are made up of cells.

Robert Hooke (1665) was the first person to discover a cell from a plant cork. The cells looked like boxes. Other people who studied the structure of cells are Lamark (1809), Detrochet (1824) and Turpin (1826).

Schleiden (1838) studied the plant cells and emphasized that the cells are organisms and entire animals and plants are aggregations of these organisms arranged according to the definite laws.

In 1839 Schwann, a German botanist stated that ” we have seen that all organisms are composed of essentially like parts namely of cells”.

IMPORTANCE OF CYTOLOGY

Cytology has been very important discipline in the research diagnosis and treatment of human diseases. Most of health problems people encounter involve the cell disturbances.

The study examines cell interaction. Studying how cells interact or relate to other cells or environments the cytologists can predict problems or examine the dangers to the cell and identity type of infections.

THE MAIN IDEAS OF THE CELL THEORY

1. All organisms are made up of cells.
2. The new cells are derived from the pre-existing cells by the process of cell division (mitotic and meiotic division).
3. All chemical reactions/metabolic activities in the bodies of the organisms take place within the cells.
4. The cells contain hereditary materials which are passed from one generation to another.
5. Given a suitable condition, a cell is capable of independent existence.

CHALLENGES OF THE CELL THEORY

 Hereditary materials are also found in viruses, mitochondria and chloroplasts, all of which are not viruses.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

STRUCTURE OF CELLS AND FUNCTIONS

The five structures are also known as ultra structure and are obtained by two techniques.

 Physiological or metabolic activities take place within a cell. Viruses though are not cells, have life within their hosts.

 The new cells arise from pre-existing cells by cell division. In this postulate the theory does not specify about the origin of the first cell.

 All living things must have cells. This postulate is challenged by the existence of viruses, where when they are inside the body of their host, viruses act as living things even though they don’t have cellular organization.

 Electronic microscope.

 Cell fractionation.

A cell is usually a tiny, three dimensional sac of many organelles which are suspended within an aqueous medium (the cytoplasm) containing or contained (bounded) by a cell membrane.

In the case of plants, a cell wall is bounded by a cellulose cell wall.

The bulk of these structures (organelles) of the cells is referred to as a cytoplasm.

Cytocil is the fluid part of the cytoplasm.

PROKARYOTIC CELLS.

They are extremely small for example bacteria all range from 0.5 – 10 micrometers.

They appeared about 350 million years ago.

Cells of prokaryotes lack the true nuclei that are their genetic material (DNA) are not enclosed by the nuclear membrane and lies freely in the cytoplasm.

EUKARYOTIC CELLS

The cells of eukaryotic have three basic parts

1. The plasma membrane.
2. The cytoplasm.
3. The nucleus.

Plasma membrane. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

This is also called the cell surface membrane as plasma membrane or plasma lemma which separates the contents of the cells from the external environment, controlling the exchange of materials.

In animal cells it is an outermost layer where as in plant cells it is beneath the cell wall. E.g. neurillema in neurons.

Muscle cells – sacrolemma.

STRUCTURE OF THE CELL MEMBRANE

There are two models suggested by different scientist to try to describe the cell membranes.

These are;

1. Daniel-Davson model (1935)
2. Fluid mosaic model (1972)

Daniel-Davson model

Diagram 1

According to Daniel and Davson, the membrane is structurally composed of two chemical substances that form their own layer.

1. Protein layer made up of molecules. The layer is continuous and lacks pores.
2. Phospholipids (at least two layers of phospholipids) oriented with their polar (hydrophilic ends near the surface and their non polar (hydrophobic) hydrocarbon chains in the interior of the membrane as far as possible from the surrounding water. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

According to the model, the membrane is structurally rigid static and non dynamic.

Strength of the model.

1. The model suggests that the membrane is composed of proteins and lipids.
2. Ampliphetic (double) nature of phospholipids such as phospholipids molecule has a polar head (hydrophilic) and a non polar tail (hydrophobic).

WEAKNESS OF THE MODEL

1. The model suggests that the protein layer is continuous. Researches done by scientists show that the protein layer is in-continuous.
2. The membrane is static is a wrong concept since the membrane is a dynamic ever changing structure.
3. Lack of pores in protein layers.

The protein molecules in a membrane have pores for passage of materials.

4. The model does not indicate the presence of a carbohydrate.

THE FLUID MOSAIC MODEL.

The model was put forward by singer and Nicolson 1972 in order to modify the Daniel and Davson model.

According to the fluid mosaic model, the membrane is an ever-changing structure in which the mosaic protein floats on the lipid bilayer acting as a fluid.

Proteins in this model do not form a continuous layer covering both sides of the membrane as proposed by Daniel and Davson model.

According to this model, the membrane has 3 constituents.

 Lipids (45%)

 Proteins (45%)

 Carbohydrates (10%)

1. Lipids.

There are two types of lipids. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Glycolipids;

These are lipids associated with short carbohydrates chain.

ROLES OF GLYCOLIPIDS

Cell to cell recognition.

Act as receptors for chemical stimuli.

1. Phospholipids;

These are lipids associated with phosphates. They form 2 layers i.e. phospholipids bilayer. Each phospholipid consists of a polar head (hydrophilic) and a non polar tail (hydrophobic). Act as a fluid and move about rapidly in their own layer. Since phospholipids are constantly in motion, the membrane is described as being fluidly.

ROLES OF PHOSPHOLIPIDS

1. Form the basic structure of the membrane.
2. Determine the fluidity of the membrane.
3. Allow the passage of fat soluble substances.

NB: cholesterol is a type of steroid located in between phospholipids keeping them fluidly.

ROLES OF CHOLESTEROL

1. Disturb the close package of phospholipids keeping them fluids.
2. Increase the flexibility of the membranes by allowing relative movements of the bilayers without actual displacement because it acts as an unsaturated fatty acid lubricating bilayer.
3. PROTEINS

These exist as globular in the membrane, i.e. they never form a continuous layer.

Within protein molecules or between adjacent there are poles. These may either be hydrophobic or hydrophilic.

Since the phospholipids are always in constant motion (fluid) proteins float in it forming a fluid mosaic model. The proteins are organized in a particular pattern known as mosaic. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

There are protein molecules that extend/ transverse both layers of membranes. Other proteins are partially embedded in the membrane. These are called intrinsic proteins.

Some proteins float freely inside the membrane, hence they are called peripheral or extrinsic proteins.

TYPES AND ROLES OF PROTEINS.

1. Carrier proteins or channel proteins.

These are involved in the selective transportation of polar molecules. i.e. ions across the membrane e.g. movement of glucose to the cell, chlorine ions. (Cl-)

2. Enzymes

Catalyze different metabolic reactions.

3. Receptor molecule.

Some act as receptors for chemical stimuli example hormones.

4. Antigen.

Identity markers. These are glycoprotein. They have different shapes in every kind of a cell. They have specific side chains thus are recognized by other cells and behave in an organized manner.

5. 5. Energy transfer. In some physiological processes such as photosynthesis and respiration, some proteins are involved in energy transfer (special form of membrane found in chloroplasts and mitochondria).
6. CARBOHYDRATES These branches to the outside of the membrane as an antennae or feelers. There are two types;
7. Glycoprotein ( carbohydrate chain – plus protein)
8. Glycolipids ( carbohydrate chain plus lipid)

They form a layer of glycocalyx MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

ROLES

1. Cell to cell recognition (in making tissues since same cells combine so similar cells will have similar glycolipids/ glycoprotein).
2. To receive chemical stimuli.

STRENGTH OF FLUID MOSAIC MODEL.

1. It realizes the presence of phospholipids bilayer and protein layer.
2. The presence of polar head (hydrophilic) and non polar tail (hydrophobic) in the phospholipids.
3. It shows that the membrane is not static.
4. It shows the presence of carbohydrates.
5. It shows that the protein layer is not continuous.
6. It indicates the presence of pores in the membrane passage of materials.

Diagram 2

FUNCTIONS OF CELL MEMBRANES.

1. It protects the cytoplasm contents of the cells.
2. It allows passage of materials in and out of the cells since it has pores.
3. In some membranes e.g. those of the intestine cells, there are microvilli which increase the surface area for absorption of materials.
4. Acts as receptor sites for chemical stimuli such as hormones.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

5. In nerve cells, the membrane is over lined with a fatty sheath (myelin sheath) which prevents the spreading of local currents to other neurons.
6. It aids cell to cell recognition when membranes of two cells come together.

VARIOUS WAYS BY WHICH MATERIALS PASS THROUGH THE MEMBRANES.

1. Permeability

The plasma membrane is a thin elastic membrane around the cell which usually allows the movement of small ions and molecules of various substances through it. This nature of plasma membrane is termed as permeability.

2. Osmosis

The plasma membrane is permeable to water molecules. To and fro movement of water molecules through the plasma membrane occurs due to the difference in concentration of the solutes on its either side. The process by which the water molecules pass through a membrane from region of higher water concentration to a region of lower water concentration is termed as osmosis.

3. Diffusion or passive transport.

The diffusion of a certain solute or substance takes place through the plasma membrane depends on the concentration and electrochemical gradient.

4. Active transport.

When molecules or ions move through the plasma membrane from low concentration to higher concentration, they require energy for such movement.

The energy is provided by ATP which is produced by the mitochondria.

Through the pores of plasma membrane some chemicals such as urea and glycerol could pass. It has been shown that large molecules of certain proteins also penetrate the cell.

5. Endocytosis and exocytosis.

The plasma membrane particles actively in the ingestion of certain large sized foreign or food substances.

The process by which the foreign substances are taken and digested is known as endocytosis. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

In the process of exocytosis, the cells which have secretory functions such as pancreatic cells pass out their enzyme secretions outside the cell.

According to the nature of the food of foreign substance, endocytosis may be classified into two types;

1. Pinocytosis

When the ingestion of food materials in bulk takes place by the cell through the process known as pinocytosis. 2. Phagocytosis Sometimes the large sized solid food or foreign particles are taken in by the cell through the plasma membrane. The process of ingestion of large sized solid substances by the cell is known as phagocytosis. Question: what is the significance of a fluid mosaic model in the plasma membrane? Ans:

 It explains easily the known physical and chemical properties of the membrane.

 It is the starting point to understanding the fix of the cell.

o All membranes of the cell plus the tonoplast and those of the organelles have the fluid mosaic construction.

NB: this point provides the clues about the distribution of cell membrane in the cell and its organelles.

NOTE:

Where

R = rate of transport of material. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

A = cross section surface area.

CYTOPLASM

This is the part of a cell, which is filled with fluid in the protoplasm. This part of the cell is the ground substance of the cell known as the hyaloplasm, where the cell organelles are suspended. Cytosil is the soluble part of the cytoplasm.

Cytoplasm is distinguished into the following structures

1. Cytoplasm matrix

The space between plasma membrane and nucleus is followed by a morphous, translucent, homogenous liquid known as cytoplasm matrix and hyaloplasm.

The cytoplasm matrix consists of various inorganic compounds e.g. carbohydrates, lipids, proteins, nucleon proteins, nucleic acids (RNA and DNA) and variety of enzymes.

The peripheral layer of a cytoplasm matrix is relatively non-glandular viscous and known as endoplasm.

2. Cytoplasm inclusion

The cytoplasm matrix contains many refractive granules of various sizes; these granules in the animal cells are known as cytoplasm inclusion.

The cytoplasm inclusion includes oil drops, yolk granules, pigments, secretory granules and glycogen granules.

Such granules in plant cells are known as plastids. The most common plastids are the chloroplasts (containing pigment chlorophyll), the leucoplastids (white color plastids) ,omyplastids ( the plastids that store starch) and lipoplastids ( which contain fats).

NB: plastids like cytoplasmic inclusion having only storage functions but also perform various important synthesis and metabolic activities such as the production of food materials due to the presence of chloroplasts.

ANIMAL CELL STRUCTURES

Diagram of the animal cells under light and electron microscope.

DIAGRAM 3 MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

DIAGRAM OF ANIMAL CELL UNDER ELECTRON MICROSCOPE MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

DIAGRAM 4

ANIMAL CELL STRUCTURES

Characteristics;

1. Have irregular shape.
2. Have centrioles.
3. Have lysosomes.
4. Lack cell walls.
5. Lack plastids.
6. Store carbohydrates in the form of glycogen e.g. phagocytotic vacuoles, pinocytotic vacuoles, autophagic vacuoles and etc.
7. Cytokinesis occurs by furrowing i.e. periphery – centres direction of constriction of cell membrane.

STRUCTURE OF THE PLANT CELL

A plant cell is incased in a tough and rigid cellulose cell wall.

Beneath the cell wall is the cell surface membrane which surrounds the cytoplasm.

The latter contains organelles; the prominent being vacuole plastids e.g. chloroplasts and nucleus. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

-Since a greater part of the cell is occupied by the vacuole, then the cytoplasm and nucleus are squeezed by the vacuole to the periphery.

-When viewed under light microscope; only a few structures are seen under high magnification power, even finer details are seen.

Diagram 5

Diagram of a plant cell under light microscope MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

DIAGRAM 6

CHARACTERISTICS OF PLANT CELLS

1. It has a fixed shape.
2. It has a cell wall made up of cellulose.
3. It has large permanent vacuole,
4. It has plastids; chloroplasts, chromoplast and leucoplasts.
5. Stores carbohydrates in the form of starch.
6. Lack lysosomes.
7. Lack centrioles.
8. Cell division; cytokinesis follows cento-periphery direction.

Similarities between a plant and an animal cell:

Both Have;

1. Plasma membrane
2. Distinct nucleus
3. Ribosome
4. Endoplasmic reticulum
5. Cytoplasm
6. Golgi apparatus
7. Qn What is an organelle?

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

An organelle is a distinct part of a cell which has a particular structure and function e.g. Mitochondria, chloroplast, ER etc.

CELL WALL

Cell wall is the structure that occurs externally to the cell.

Organisms with cell wall include.

8. Bacteria – have cell wall made up of murein and peptidoglycogen.
9. Fungi – has cell wall made up of chitin.
10. Algae and plant have cell wall made up of cellulose.

Plant cells cell walls.

It is the structure external to the cell; it isn’t an organelle although it is a product of various cell organelle e.g. microtubules and Golgi apparatus.

CHEMICAL COMPOSITION.

It is made up of cellulose (mainly fibres) forming amorphous matrix of the cellulose that surrounds the entire cell.

Such fibre is made up of several hundred microfibrils which form the network of cell wall.

In addition to cellulose plant cell wall consists of pectron and hemicellulose which contribute to mechanical strength of the organism.

Pectron

These are polysaccharides of galactose and galactronic acid. Pectron may combine with Ca2+ or Mg2+ to form calcium pectate or magnesium pectrate, which are important components of the first layer of cell wall to be laid down on middle lamella.

Hemicellulose MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Hemicellulose is the mixture of many compounds, but the chief ones are sugar e.g. glucose and sugar acid residue.

Hemicelluloses which form hydrogen bounds with cellulose fibres in the cell matrix. The cell wall is usually modified by deposition of other substances such as alginic acid and calcium carbonate in the case of algae.

Functions of cell wall.

1. Mechanical support and skeletal support of individual cell and plants as well. This is through lignifications.
2. To prevent cell from bursting in hypotonic solution.
3. Control cell growth and shape. Orientation of cellulose microfibrils limits and helps to control cell growth and shape because of the cells ability to stretch is determined by their arrangements.
4. Movement of water and material salts.

The system of interconnected cell walls (apoplast) is a major pathway of the movement of water and dissolved mineral salts.

The cell walls are held together by middle lamellae, they also posses minute pores through which structures called plasmodesmata form living connections between cells and allows the protoplast to be linked in a system called symplast.

5. Reduction of water loss and reduced risk of infection (due to its waxy cuticle).
6. Transportation of materials. The walls of xylem vessels and sieve tubes are adopted for long transportation of materials through the cells.
7. Barrier to water movement.

The cell walls of root endodermal cells are impregnated with suberin that forms a barrier to water movement.

8. Some cell walls are modified as food reserves as in the storage hemicelluloses in some seeds.
9. Transport of materials by active transport.

The cell wall of transfer cells develops an increased surface area and this increases the efficiency and transfer materials by active transport.

CELL ORGANELLES OR ORGANOIDS. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Besides the cellular inclusion and plastids, the cytoplasm matrix contains many large sized structures known as cell organelles or organoids which perform various important synthesis, transportation, support and

reproduction.

These organelles are the endoplasmic reticulum, ribosome, Golgi complex, liposomes, mitochondria, plastids, centrioles, cilia etc.

Functions of cytoplasm

1. It provides medium for chemical reaction to take place like protein synthesis, lipids synthesis and etc.
2. It stores useful materials such as amino acids, proteins, starch, carbohydrates, lipids, O2 etc.
3. It stores waste materials such as C02 and nitrogen waste etc.
4. It controls the absorption of materials across the membrane due to its concentration gradient.

CELL ORGANELLES

1. ENDOPLASMIC RETICULUM

Is the cytoplasm matrix, is transverse by a vast reticulum or network at interconnecting tubules and vesicles which is known as endoplasmic reticulum or ER.

The endoplasmic is having a single vast and interconnected cavity which remains bounded by a single membrane. The membrane of endoplasmic reticulum is supposed to be originated in pushings of plasma membrane

in the hyloplasm (matrix) because chemically it consists of a lipoproteinous structure like plasma membrane.

The membrane of the endoplasmic reticulum may be either smooth when they do not have attached ribosome and rough when they have the attached ribosome.

The membranes of endoplasmic reticulum are found to be continuous with the nuclear membrane and plasma membrane.

FUNCTIONS OF ENDOPLASMIC RETICULUM MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Transport of materials from exterior to the nucleus or to cytoplasm organelles such as Golgi complex.
2. It provides mechanical support to the cytoplasm matrix.
3. Functions as a cytoplasm framework.

Surfaces for some of the biological activities of the cell catalyst its complex folding provide an enormous surface for such activities.

4. Synthesis and transfer of lipids.( smooth endoplasmic reticulum)
5. In the liver the smooth endoplasmic reticulum detoxifies many poisons and drugs.
6. The rough endoplasmic reticulum transports proteins synthesized in the ribosome of the rough endoplasmic reticulum.
7. Formation of Golgi bodies as they are modified endoplasmic reticulum.
8. Routes for movement of materials from the nucleus to the cytoplasm.

DIAGRAM 7

2. GOLGI APPARATUS/ DICTYLOSOMES This cell organelle is also known as the Golgi body, Golgi complex or sityasome. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

DIAGRAM 8

It is the apparatus which consists of membranous sacs called cisternae and a system of small vesicle (called Golgi vesicles or dictysome vesicles) and vacuoles of various sizes.

The membranes of Golgi complex are of lipoproteins and these are supposed to be originated from the membrane of endoplasmic reticulum.

FUNCTIONS

1. Produce secretions

There are many Golgi apparatus in;

 Cells of salivary gland

 Cells of root cap

 Cells of endocrine glands i.e. pancreas

2. Modification of materials.

The combination of carbohydrates and proteins to form glycoprotein takes place in them. Many materials such as mucin are glycoprotein. It takes place in the cistern.

Carbohydrate chain + lipids = glycolipids

3. Production of carbohydrates example cellulose produced in plants after division. Thus this separates one cell from another. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

4. Transport of lipids (storage and transport of proteins and lipids) after digestion, the fatty acids and glycerol are formed. In the endoplasmic reticulum fatty acids and glycerol unite to form lipids (triglycerides). The latter are passed to the Golgi apparatus where it transports them to the plasma membrane as lymphatic system and going to the lymphatic system.
5. Formation of lysosomes.
6. Synthesis of various types of carbohydrates from simple sugars.
7. It activates the mitochondria to produce ATP.
8. It forms the acrosome of the sperms.
9. LYSOSOMES.

These are spherical single membrane bound organelles containing digestive enzymes.

-lipase

-carbohydrases

– Nucleases

The enzymes are synthesized in ribosome RER transported to the Golgi apparatus for modification. The Golgi vesicles are detached from the Golgi apparatus and remain in the cytoplasm as lysosomes because they contain digestive enzymes.

FUNCTIONS

1. Functions as storage vesicle for many powerful digestive (hydrocytic) enzymes.
2. Acts as digestive system of the cell enabling it to process some of the bulk materials taken in by phagocytosis or pinocytosis. Digests parts of the cell such as worn out organelles and also to digest the stored food contents of chloroplast A and B in extracellular digestion.
3. Play role in some developmental process e.g. remolding of bones and fractures.

NB: in plant cells, the large contrast vacuole may act as lysosomes although bodies similar to lysosomes of an animal cell sometimes seen in the cytoplasm of a plant cell. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

4. RIBOSOMES.

Structurally it has two sub-units, i.e. small subunit and large subunit.

Each of the two subunits is composed of rRNA (ribosomal RNA) and proteins.

It is present in both eukaryotic and prokaryotic cells. The sizes can be determined by the sedimentation when centrifuging showing the 80’s and 70’s ribosome.

-80’s ribosome are present in R.E (rough endoplasmic) reticulum of eukaryotic cells.

-70’s ribosomes are present in prokaryotes as well as mitochondria and chloroplasts of eukaryotic cells.

FUNCTIONS OF RIBOSOMES

1. They provide large surface area for protein synthesis.
2. They are binding sites of the RNA.

ADAPTATIONS OF RIBOSOMES.

The ribosomes are the sites for protein synthesis. it has the following characteristics.

1. Presence of enzymes capable of catalyzing the synthesis of peptide bonds.
2. Presence of ribosomal RNA (rRNA) that attract other types of RNA i.e. mRNA and tRNA towards the ribosome’s.

5. VACUOLES
6. A vacuole is a fluid filled sac which is bound by a single membrane.

In animal cells, there are relatively small and temporary vacuoles such as phagocytotic, pinocytotic, autophagic vacuoles in plant cells; the vacuole is large and occupies a greater proportion of the cytoplasm.

The membrane bounding the vacuole is the tonoplast and the fluid inside is the cell sap or vacuole sap. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

The cell sap is a mixture of many substances; concentrates solutions of sugar, salt, organic acids, gases such as C02 and oxygen, pigments and waste products of metabolism.

It also contains enzymes similar to those of lysosomes.

ROLES OF CELL VACUOLES

1. They are involved in primary plant growth. It is a result of turgor pressure generated inside the vacuoles as a result of entry of water. This causes cell expansion as the tonoplast is pressed against the cell wall.
2. The pigment contained in the cell sap is responsible for flower color and therefore play a key role to pollination.
3. They contain enzymes similar to those of lysosomes when plant cell dies. The tonoplast looses the differential permeability and enzymes escape causing autolysis.
4. Vacuole acts as a temporary store of waste products such as crystals of waste calcium oxalate, toxins and metabolic waste products of plants.
5. The vacuoles sometimes functions as food reserves e.g. sucrose mineral salts and insulin are stored in vacuoles.
6. In prokaryotes it serves for buoyancy.
7. MITOCHONDRIA

Structure of mitochondria

It is a sausage shaped or an oval shaped organelle surrounded by a double membrane (mitochondrial envelope). The envelope consists of the outer and inner membrane.

Between the two membranes there is a space, the intermembranal space.

The outer membrane is smooth while the inner membrane is coiled to form t=surface area for attachment of membranes.

The ground substance of the mitochondrion is called matrix. This contains

1. Several enzymes responsible for Krebs cycle.
2. Circular DNA that resembles that of prokaryotic cells. It is for self replication of mitochondria.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

3. 70s ribosome like those of prokaryotic cells. These are for protein synthesis e.g. enzymes

Diagram of mitochondrion 9

Functions of mitochondrion

The main function of mitochondrion is to yield energy during respiration.

About 98% of energy is synthesized e.g. one molecules of glucose yield 38 ATP. Out of 38ATP 36 is synthesized in the mitochondrion by the reactions of Krebs cycle and electron transport chain. Thus it is called power house or POWER station or power plant of the cell.

Adaptations of the mitochondrion to energy productio

1. Presence of outer membrane and inner membrane to allow entry and exit of materials.
2. The inner membrane is coiled to increase the surface area for attachment of enzymes responsible for electron transfer.
3. Presence of matrix which is as granular and gives enough space for reaction to take place (Krebs cycle reaction) also matrix contains Krebs cycle enzymes.
4. Presence of circular DNA for replication of the mitochondrion.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

5. Have 70s ribosome’s for synthesis of proteins.
6. Presence of phosphate for production of ATP.
7. Presence of Oxysome and water accompany aerobic respiration.

NB: the inner folded to form partitions called cristae which enables different types of metabolic activities to take place. This phenomenon is called compartmentalization hence enables multi-enzymes systems to operate.

ENDOSYMBIOTIC THEORY

(Evolution of mitochondria)

The mitochondria were originally independent prokaryotic bacteria like organisms which entered hosts cells and develop mutual relationship (symbiosis).

MITOCHONDRIA AS PROKARYOTIC CELL

1. Posses its own DNA and is able of self replication / reproduction.
2. Have a circular like bacteria DNA.
3. It is sensitive to different antibiotics such as chlorophyll and streptomycin which inhibit mitochondrial activities.
4. It contains ribosomes similar to those of bacteria.

7. 7. PLASTIDS These are organelles with double membrane, located in plant cells and algae

Types

1. Chromoplasts
2. Leucoplasts
3. Chloroplasts
4. CHROMOPLASTS

(Chromo – color / pigment)

These are types of plastids bearing pigments i.e. yellow, red, orange, purple pigments.

Found in MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Flowers
2. Fruits
3. Seeds
4. Leaves
5. Roots of carrots.

2. LEUCOPLAST (embryos and germ cells)

Leuco- colour / white.

These are colour plastids found mainly in storage organs. There are various types of leucoplasts;

1. Amyloplasts- contain starch
2. Lipoplasts – stores lipids
3. Proteoplasts- stores proteins

Structure of chloroplasts

The chloroplast

-the chloroplast is an oval shaped green in color due to presence of chlorophyll.

– It has two membranes an outer and an inner membrane which constitutes the double membrane or chloroplast envelope.

-Between the membranes there is the inter membrane space.

– The ground substance of the chloroplast is the stroma.

– The latter has a system of parallel running membranes called thylakoids.

-the interval between one grannum and the other is called intergranal lamellae.

– The stroma contains circular DNA and fewer small 70’s ribosomes and starch granules.

Functions of chloroplasts

1. It is the site of photosynthesis.

This is the process whereby green plants manufacture food from CO2 and water in the presence of light energy, it stores starch temporarily. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

2. The thylakoids have chlorophyll pigment for trapping sunlight energy.
3. It has grana and thylakoids to hold the chlorophyll in proper position for maximum absorption of light energy.
4. Stroma contains enzymes for dark reactions of photosynthesis.
5. Presence of phosphate which acts as a source of phosphate during phosphorylation.
6. Ribosomes and circular DNA for synthesis of proteins such as enzymes

Endosymbiotic nature of chloroplasts and mitochondria.

The chloroplast and the mitochondria are endosymbiotic structures within a cell. They are capable of leading life within a cell because;

1. They have double membrane which allows passage of materials in and out of their inside.
2. They have their own hereditary materials i.e. circular DNA. They are capable of self replicating.
3. They have ribosomes (70’s) thus synthesize proteins. E.g. enzymes.
4. Have matrix or stroma, the ground substance where various reactions take place.

STROMA; various photosynthetic membrane are found where light reactions take place and dark reactions in the aqueous part.

MATRIX: Krebs cycle of respiration.

5. They have their own enzyme system.

Therefore chloroplasts and mitochondria are said to be cells within cells.

The endosymbiotic nature of chloroplasts and mitochondria can be described as serial endosymbiotic theory (SET).

SERIAL ENDOSYMBIOTIC THEORY.

This theory accounts for the evolution of eukaryotic cells from prokaryotic cells.

Evidence / similarities of organelle and prokaryotic cells

 Double membrane as cell membrane.

 Circular DNA.

 70’s ribosomes.

 System of enzymes.

MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

SERIAL ENDOSYMBIOTIC THEORY.

It was suggested that mitochondrion, chloroplasts are descendants of ancient prokaryotic organisms.

-Eukaryotic cells arose from invasion of one large cell by other prokaryotic cells.

The SET states that;

“All eukaryotic cells contain genetic material (DNA) ribosomes that resemble those of prokaryotic cells’’.

-It suggests that prokaryotic heterotropes ingested other mitochondrion like prokaryotic and roughly at the same time began forming an organized nucleus.

Subsequently, non motile cells established a symbiotic relationship with yet another prokaryote in the form of spirochetes or spiroplasma bacterium, attached to the outside of the cell. Such as bacterium has a function like flagellum.

Eventually a photosynthetic prokaryote engulfed by this regardless as a primitive plant cell.

QNS

1. Chloroplasts, mitochondria and bacteria have features in common. Enumerate the features to reveal the truth of this statement.
2. Where in the body would you expect to find large number of mitochondria? Give reasons.
3. If mitochondria were to perform the function of the function of the chloroplast, what modification would it require.

8. MICROBODIES OR PEROXISOMES

These are small spherical bodies with 0.5 – 1.5 micrometers in diameter. The ground substance of a micro body contains important enzymes especially catalyze or peroxidase.

These enzymes catalyse the hydrolysis of hydrogen peroxide in water and oxygen.

These peroxisomes are found in liver, potatoes, pea seeds and bean seeds. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Diagram 10

FUNCTIONS OF PEROXISOMES

1. To break down the poisonous hydrogen peroxide to water and oxygen in the presence of peroxidase enzyme/ catalase.
2. In plants special peroxisomes called glycoxisomes are centre’s for glycoxylate cycle i.e. conversion of fats into carbohydrates especially during germination.

3.The leaf of peroxisomes are centers of photorespiration, especially in C3 plants e.g. beach plants, potato plant, tomato, coffee in cold areas.

CYTOSKELETON

This is a complex network of fibrous protein structure that exists in cytoplasm of eukaryotic cell and anchor proteins or organelles such as nucleus to their fixed location.

The structures which constitute cytoskeleton include;

1. Microfilament( actin filaments)
2. Intermediate filaments
3. Microtubules

1. MICROFILAMENTS(ACTIN FILAMENTS)

These are thread like structures arranged in sheets or bundles first beneath the cell surface membrane. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Diagram 11

-Chemically they contain actin and myosin.

-Each fibre is composed of two chains of protein loosely twisted about one another in helical manner. These proteins molecules can be assembled and dis-assembled.

FUNCTIONS

 Interactions of these fibres with myosin help in muscle contraction.

 Determine the shape of cell’s skeleton.

 Responsible for movement of materials within the cells.

 Cleavage of animal cells is brought about by the constriction of a ring of microfilaments after nuclear division, cytokinesis.

2. INTERMEDIATE FILAMENTS. These are structures intermediate between microtubule and microfilament (rope like microtubule of polypeptides)

Skin cells for example form intermediate filaments from proteins called KERATIN. When the skin dies the intermediate filament of the cytoskeleton persists. Hair and nails are formed this way. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

FUNCTION

1. Provide cells shape
2. Act as intercellular tendons preventing excessive stretching of cells.
3. MICROTUBULES

Microtubules are tubular structures made up of helizelly arranged globular subunit called tubulin.

-They are about 25 nm in diameter. Each has a chain of proteins wrapped round and round in a tight spiral. Large microtubules are found in cilia, flagella, centrioles (formation of spindle- fibres microtubules).

Functions

1. They bring about movement of chromosomes during metaphase in nuclear division.
2. Since they are tubular, they transport materials from one part of the cytoplasm to another, i.e. they are cytoconductors.
3. In cilia and flagella, they help in rhythmical beating up movement.
4. They determine the shape of the cell. (Skeletal support).

9. CILLIA AND FLAGELLA.

The cells of many unicellular organisms and ciliated epithelium of multi-cellular organisms consists of some hair like cytoplasm projections outside the surface of the cell.

-These are known as cilia or flagella and they help in locomotion of the cells. The cilia and flagella are made up of proteins adenosine triphosphate (ATP).

-In prokaryotic cells, cilia and flagella (If they have structure lacking 9+2 arrangement of microtubules and arise from basal bodies).

-In eukaryotic cilia and flagella are complex. They have the 9+2 arrangement of microtubule and arise from basal bodies.

10. CENTRIOLES.

Centrioles are present in animal cells only.

-They are two placed at right angle to each other.

-A number of rays called ultra rays usually surround the centrosomes. MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

Each centriole is composed of nine paired thin threads and is in the form of cylinder.

They aid in cell division.

11. PINOCYTOTIC VESSICLE

These are organelle formed as a result of in folding of plasma membranes as it takes large particles of food from outside the cell.

The process is called pinocytosis.

Eventually pinch off and form very small vacuole (vesicle).

FUNCTIONS

Transport large particles into the cell.

12. NUCLEUS.

-Nucleus is the functional unit of a cell.

It contains materials which control different activities within the cell; the genetic materials.

STRUCTURE OF THE NUCLEUS.

The nucleus has a membrane called nuclear membrane envelope.

Then nuclear membrane has some pores which allow some materials to pass in and out of nucleoplasm to allow communication on with cytoplasm called nuclear pores.

-Nuclear pores are made up of non-membrane materials forming nuclear pores.

-Nuclear envelope is semi permeable membrane allowing some materials to pass and others not to pass.

-The space inside the nucleus is filled by fluid materials which are called nucleoplasm. These are semisolid granules ground substance or matrix.

Within the nucleoplasm there are two components; MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Nucleolus
2. Chromatin
3. Matrix (aqueous)

Chromatin threads

Chromatin threads are grainy network of strands that undergo cooling into rod-like structures called chromatin.

Chemically chromatin and therefore chromosomes contains DNA (deoxyribose nucleic acids) and much protein and some RNA (ribonucleic acids) and few minerals.

Nucleolus

These are small dark regions where different RNA type examples ribosomal RNA is produced and RNA joins the protein to form the subunit of ribosomes.

-It synthesizes the ribosomes protein and is used in controlling the cell division.

Functions of nucleolus

1. Controls all metabolic activities of the cells
2. It regulates cell division.
3. Concerned with transmission of hereditary traits from parent to offspring.
4. Synthesizes and stores proteins.

PROKARYOTIC CELL

1. A WELL LABELLED DIAGRAM OF A BACTERIAL CELL.

DIAGRAM 12 MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

PROKARYOTIC CELL e.g. bacteria, cyano bacteria.	EUKARYOTIC CELL e.g. protoctista, green plants, animal and fungi.
1. Usually extremely small cells.	Usually large cells about 10-100 micrometer
2. Nucleus absent, naked circular DNA	Distinct nuclear region DNA helical shaped enclosed in a protein coat.
3. No nucleus.	Nucleus present
4. Few organelles and non are surrounded by an envelope (double membrane).	Many organelles envelope(bound) organelles ( i.e. double membrane bound organelles)
5. Internal membrane if present usually associated with respiration or photosynthesis.	Great diversity of internal membrane organelle e.g. Golgi apparatus, lysosomes, ER.
6.Flagella are simple lacking arrangement of microtubule.	Complex flagella with ( 9+2) arrangement of microtubule.
7. Have mesosome for respiration.	Use mitochondria for respiration
8. Some are nitrogen fixing.	No ability to fix nitrogen.
9. 70’s ribosomes.	80’s ribosomes

 

Similarities between prokaryotic and eukaryotic cells.

Both have; MPELLA EDUCATION BLOG www.rajmpella.blogspot.com

1. Structure for movement (cilia and flagella)
2. Cell wall.
3. Cell membrane.
4. Ribosome’s.
5. Genetic material.(DNA)
6. Storage of food organelles.

QUESTIONS

1. a. Give the principle constituent of the cell membrane.

1. Draw a fully labeled diagram to illustrate the arrangement of these constituents and others in the fluid mosaic model of the cell wall membrane.
2. why is the model described as being fluidy?
3. Give two functions of the cell membrane.
4. Describe the role of the following membranous organelles; lysosomes, endoplasmatic reticulum, ribosome’s and Golgi apparatus.

CELL DIFFERENTIATION

This is the specialization of a cell in terms of both structure and functions. Ability of a cell to perform single function is called cell specialization. Cells work in interdependence with each other such that such that group of cells must be coordinated so that they carry out their activities efficiently such coordination is called integration.