BIOLOGY FORM ONE TOPIC 3: CELL STRUCTURE AND ORGANIZATION, TOPIC 4: CLASSIFICATION OF LIVING THINGS
TOPIC 3: CELL STRUCTURE AND ORGANIZATION
The Concept of Cell
The Meaning of the Cell
Explain the meaning of the cell
and animals are made up of units called cells. The cells are
microscopic in such a way that they cannot be seen by our naked eyes.
Some organisms like protozoa, diatoms and bacteria consist of one cell
and are called single-celled or unicellular organisms. Some are made up
of many cells and are called multicellular organisms.
cell structure of living things was first seen by Robert Hooke in 1667
when he examined fine slices of cork. Robert Hooke believed that the
cells were empty and that the cell wall and cell membrane were the most
important parts of the cell but now cell contents are seen to be the
most important ones. Therefore a cell can be defined as the smallest unit of living things or a cell is a basic unit of life.
The Characteristics of the Cell
Mention the characteristics of the cell
Characteristics of the cell include the following:
Cells are small microscopic structures which cannot be seen by our naked eyes.
Cells are capable of dividing by mitotic process or meiotic process.
Cells contain structures called organelles.
The cell theory
A cell is a basic unit of structure and function in living organisms.
New cells only come from pre-existing ones.
Cells contain structures called organelles.
cell theories were proposed jointly by two scientists namely Schleiden,
a Belgian botanist, in 1838 and Schwann, German Zoologist, in 1839
Difference Between Various Types of Cells
Differentiate various types of cells
PROKARYOTIC AND EUKARYOTIC CELLS
are cells with no membrane-bound nucleus. The DNA lies free in the
cytoplasm in a region known as nucleoid. They have no true nuclei.
Examples of prokaryotic organisms are bacteria.
Eukaryotic cells are
cells whose nuclei are bounded by nuclear membrane. They are surrounded
by two nuclear membranes called nuclear envelope. Examples of
eukaryotic organisms are protoctists, fungi, plants and animal cells.
Differences between cell wall and cell membrane
It is a non–living structure
It is a living structure
It is made up of cellulose
It is made up of lipoprotein
It is freely permeable
It is selectively permeable
Different between prokaryotic and Eukaryotic cells
They have nuclear membrane
Lack nuclear membrane
Organelles are surrounded by envelopes
Organelles are not surrounded by envelopes
Have true nucleus
Have no true nucleus
The Functions of Different Parts of Plant and Animal Cells
Explain the functions of different parts of plant and animal cells
Basically a cell has three main parts
Cell membrane (plasmalemma)
This is a thin flexible membrane made of protein and oil. It has the following functions:
The cell membrane encloses the contents of the cell.
is freely permeable to water and gases only and selectively permeable
to other molecules e.g. it allows food in but keeps unwanted molecules
out. Thus cell the membrane controls the substances entering and leaving
is a transparent jelly-like fluid and may contain particles such
chloroplasts or starch grains or oil droplets. It contains up to 80%
water and the remainder is mainly protein. It is a place where chemical
reactions take place
nucleus is a ball-shaped or oval body located inside the cytoplasm. It
cannot usually be seen unless the cell has been stained with certain
dyes. It consists of nucleoplasm bounded by nuclear membrane. The
nucleus is a cell control centre.
The following are the functions of the nucleus:
It controls the formation and development of a cell.
The nucleus also controls chemicals which the cell manufactures.
The nucleus contain chromosomes which carry genetic material i.e. DNA which is responsible for controlling genetic information.
cell wall is only found in plant cells. It is made up of cellulose.
When the cell is growing the cell wall is fairy plastic and extensible.
It becomes tough and resists stretching when the cell has reached full
size. The cell wall is non-living. It has the following functions:
It gives the cell its shape.
It is freely permeable to all kinds of molecules.
It supports and protects the cell.
It supports non-woody plant organs, such as leaves, by turgor pressure.
It osmoregulates by resisting entry of excess water into cell.
animal cells, vacuoles are small droplets of fluid in the cytoplasm
variable in size and position. In plant cells, the vacuole is a large,
permanent fluid-filled cavity which occupies a greater part of the cell.
In plants, the fluid is called cell sap. The cell sap may contain salts, sugar and pigments dissolved in water.
The vacuole performs the following functions:
It is responsible for food storage and osmoregulation.
The outward pressure of the vacuole on the cell wall makes the plant cells firm, giving strength and resilience to the tissues.
are found in all aerobic eukaryotic cells. A mitochondrion is
surrounded by an envelope of two membranes, the inner being folded to
form cristae (singular: crista) It contains a matrix with a few ribosomes, a circular DNA molecule and phosphate granules.
mitochondrion is a power house of a cell. It contains respiratory
enzymes involved in respiration. It absorbs oxygen and glucose. The
glucose is broken down to CO2 and H2O. Energy is released from glucose bonds to form ATPs (for use in other vital functions e.g. growth, movement, etc.
are disc-shaped organelles. They are found in plant cells and algae
cells. A chloroplast contains a green substance called chlorophyll. It
is surrounded by an envelope of two membranes and contains gel-like
stroma through which runs a system of membranes that are stacked in
places to form grana.
is an organelle in which photosynthesis takes place, producing sugars
from carbon dioxide and water using light energy trapped by chlorophyll.
Golgi bodies are stacks of flattened, membrane-bound sacs
Golgi bodies have the following functions:
Golgi bodies are responsible for internal processing and transport system.
Processing of many cell materials e.g. protein takes place in the cisternae.
Godgi vesicles transport the materials to the other parts of the cell
Plant and Animal Cell
Draw and label plant and animal cell
Similarities and Differences of Plant and Animal Cells
Outline similarities and differences of plant and animal cells
Differences between plant cell and animal cells
(i) Have definite shape
Have no definite shape
(ii) Have chloroplasts
Have no chloroplasts
(iii)Have large permanent vacuoles
Have small temporary vacuoles
(iv) Centrioles usually absent
(v) Have cell wall made of cellulose
Have no cell wall
(vi) The nucleus is located at the periphery
The nucleus is centrally located
Similarities between animal cell and plant cells
Both have cell membranes
Both contain cytoplasm
Both have nucleus
Both have mitochondria
Both have golgi bodies
Both have ribosomes
The Concept of Cell Differentiation
Explain the concept of cell differentiation
When most cells have finished dividing they become specialized. This means that:
They do one particular job
They develop a distinct shape
Special kinds of chemical change take place in their cytoplasm
changes in shape and chemical reactions enable the cell to carry out
its special function. The process by which cells are specialized to
perform a particular function is called cell differentiation or ‘division of labour’
within the organism. Similarly, the special functions of mitochondria,
ribosomes and other cell organelles may be termed as division of labour
within the cell.
The Importance of Cell Differentiation and Formation of Tissues, Organs and Body Systems
Outline the importance of cell differentiation and formation of tissues, organs and body systems
Humans have many different types ofcellswith different jobs, such as bloodcellsthat carry oxygen and nervecellsthat transmit signals to all parts of the body.Cell differentiationis the process by whichcellsbecome specialized in order to perform different functions.
multicellular organisms begin as just a single cell. Getting from one
single cell to billions of specialized cells that perform different
functions is a process that happens with the regulation of DNA and RNA.
It can also be influenced by factors in the environment.
differentiation holds a lot of importance for two basic reasons.
Firstly, it helps to identify stem cells, which could be used in the
future to deal with conditions that require transplant and form the
basis of embryonic stem cell research. Also, in cytopathology, the level
of cellular differentiation is used as a measure of cancer progression,
where the term ‘grade’ is used as a marker to determine how
differentiated a cell in a tumor is. Thus, the importance of this
process cannot be underestimated as it could hold the key to future
treatments for fatal diseases.
Difference between Cells, Tissues Organs and Body Systems
Differentiate cells, tissues organs and body systems
are specialized for conducting impulses of an electrical nature along
the fibre. The fibre may be very long e.g. from the foot to the spinal
column. They are the longest cells known.
White blood cells:These
cells occur in blood stream and are specialized for engulfing harmful
bacteria. They are able to change their shapes and move about, even
through the walls of blood vessels into the surrounding tissue.
White blood cell
Red blood cells:These cells are responsible for transportation of oxygen from the lungs to all parts of the body.
Red blood cells
Platelet cells: Platelet
cells are found in the blood. They are also called blood platelets.
Their function is to help clot the blood at wounds and so stop bleeding.
Sperm cell: it is a male gamete produced in the testes.
Egg cell:It is a female gamete produced in the ovary.
are elongated cells which form the muscle tissues. Muscle cells are
highly specialized in that they are able to shorten a half or even a
third of their resting lengths. This characteristic enables the muscles
to contract and expand.
These cells form the lining of the nose and wind pipe.
Root hair cells
cells form the outer layer of young roots. The cells are specialized to
absorb water and mineral slats from the soil. The hair-like projections
penetrate the soil particles and offer a large absorbing surface.
are food conducting cells in a plant, joined end to end, and where they
meet, perforations occur in the walls. Through these holes, the
cytoplasm of one cell communicates with the next.
cells conduct water and mineral salts form the soil to all parts of the
plant. They are also responsible for mechanical support.
A tissue is a group or collection of similar cells performing a specific function. Tissues vary in size, shape and function.
Examples of tissues
Animal tissues include epithelial tissue, muscle tissue, nervous tissue, blood tissue and bony tissue.
tissues cover the body lining cavities, hollow organs and tubes. They
are responsible for(i) protection of the underlying structure from
dehydration, and chemical and mechanical damages;(ii) secretion;
Cilliated columnar epithelium with goblet cells
Muscle tissue consists of cells specialized to contract and move the body. Muscle tissues can be:
skeletal muscle tissue;
smooth muscle tissue; or
cardiac muscle tissue.
Skeletal muscle tissues form those muscles that move the bones
Skeletal muscle fibres
Smooth muscle tissues
These are found in the walls of hollow organs. They perform the following functions:
Regulate the diameter of blood vessels and parts of the respiratory tract.
Propel the contents of the ureters, ducts of glands and alimentary tract.
Expel contents of the urinary bladder and uterus.
Smooth muscle fibres
Cardiac muscle tissue
kind of muscle tissue is found only in the heart wall. It helps in
contracting and relaxing of heart muscles thus pumping the blood to
various body parts.
Cardiac muscle fibres
tissues have endings that detect changes in the environment. They
transmit and conduct nerve impulses to the brain and spinal cord and to
the effector organs.
of plant tissues are collenchyma tissue, sclerenchyma tissue, epidermal
tissue, conducting tissues e.g. phloem and xylem, palisade tissue and
An onion epidermal tissue
An organ is a collection of tissues working together to perform a certain function
Other examples of animal organs include skin, testes, ears, noses and the brain.
Examples of plant organs include leaves, stems, roots, flowers and fruits.
A system refers to several inter-related organs performing a particular function.
main organs that make up the digestive system are alimentary canal,
liver and pancreas.The main function of this system is to digest and
The digestive system
system consists of the heart, arteries and veins.The role of the
circulatory system is to transport gases, food, hormones and distribute
The circulatory system
system has comprises of the lymph vessels and lymph nodes. The main
function of the lymphatic system is to transport materials and protect
respiratory system consists of the trachea and the lungs. The role of
the respiratory system is to take in oxygen and expel carbon dioxide
The respiratory system
The urinary system
main organs of the urinary system are kidneys, ureter, bladder and
urethra.The urinary system plays a role in removing metabolic waste
products from the body and also it is responsible for osmoregulation.
The nervous system
This system consists of the brain, spinal cord and nerves.The role of the nervous system is to detect and respond to stimuli.
The muscular system
It consists of the organs muscles and tendons. The role of the muscular system is to bring about movement.
The skeletal muscles
The reproductive system
It consists of the ovaries, testes and uterus. Its role is to produce offspring.
Male reproductive system
Female reproductive system
It consists of endocrine glands. Its role is to produce hormones.
It consists of a system of skeletons. Its function is to support the body, protect internal organs and produce blood cells.
Examples of organ system in plants
Root system –consists of roots
Holds the plant firmly into the soil
Absorption of water and mineral salts from the soil
Sometimes they act as storage organs in some plants
Shoot system – consists of the organs flowers, fruits, stem and leaves
Site of reproduction
Transport of substances
Photosynthesis occurs in the shoot
TOPIC 4: CLASSIFICATION OF LIVING THINGS
Concept of Classification
The Concept of Classification
Explain the concept of classification
you ever visited a library? How are the books arrangedand kept? Are
they arranged randomly or systematically? Obviously the books are
arranged systematically in the shelves. Science books are kept
separately in their respective shelves. Science books are kept
separately from social or commercial books. Biology books are separated
from physics books or chemistry books. Likewise, in the shop, laboratory
or pharmacy items are sorted and placed on the basis of their
the world, there are numerous varieties of living organisms.These
organisms do vary in size, structure, shape, habitat, modeof feeding and
even mode of reproduction. The organisms can be sorted out and placed
into different groups based on their similarities. The system of sorting
out and placing organisms into different groups on the basis of their
similarities and differences is called classification.
Living Things According to Their Similarities and Differences
Group living things according to their similarities and differences
the external features of the following organisms:Lizard, sugar cane
plant, maize plant, shark, Tilapia, cactusplant, bat, cockroach,
butterfly, hen, goat, toad, frog, spider andorange plant
Sort out the above organisms into plants and animals
Classify the animals on the following basis
Those with wings and those without wings
Those with tails and those without tails
Those with antennae and those without antennae
Terrestrial and aquatic organisms
The Importance of Classifying Living Things
Explain the importance of classifying living things
The following are importances of classification
Classification makes the study of living things easy
Classification makes communication easy among biologists from different parts of the world
It provides good organized system in which a newly identified organism can be easily fitted in future.
It makes it easier to identify organisms
It can be used to predict characteristics that are present in the members of the same group.
Types of Classification Systems and Their Differences
Outline types of classification systems and their differences
There are two types of classification
classificationAn artificial classification is based on one or a few
easilyobservable characteristics and usually designed for
practicalpurpose with an emphasis on convenience and simplicity. In
thistype of classification, unrelated organisms are often placed inthe
same group while closely related organisms are often placedin different
groups.Linnaeus included all
included all worm-like organisms in a single group,the vermes. This
included wide a range of animals as fromnematodes, earthworms to snakes.
This was an artificialclassification since it did not consider natural
relationships suchas the fact that snakes have backbones and earthworms
do nothave. Thus, snakes have more features in common withvertebrates
than with worms.
and birds would be placed in the same group because allhave the ability
to fly since they posses wings. But bats sharemany features with
mammals. They have features like hair,mammary glands, sweat glands and
different types of teethwhich are characteristics of mammals. Therefore,
bats are morerelated to mammals than birds.Natural
system of classificationThis type of classification system tries to use
natural relationshipsbetween organisms. It considers many features in
commonincluding internal as well as external features.Similarity of
embryology, morphology, anatomy, biochemistrycell, structure and
behaviour are all considered relevant. It isbased on evolutionary
relationship in which organismsbelonging to the same group are believed
to have a commonancestor.
features which show homology are distinguishedfrom those which show
analogy. Example the fore limbs ofmammals, whales, birds and bats have
the same basic patternand similar bone arrangement, i.e. homologous.
This suggeststhat these organisms are coming from the same ancestor and
thatcan be placed in the same group.
wings of birds and grasshoppers are analogous. The wingsof birds have
internal skeletons while the wings of grasshoppersdo not have bones but
they perform similar function. Theseorganisms cannot be placed in the
same group since they aredifferent in many ways.
Merits and Demerits of Each Type of Classification System
Explain merits and demerits of each type of classification system
Advantages of artificial system of classification
It is easy to classify organisms since it is based on few observable characteristics.
It does not take much time to classify organisms based on this system (not time consuming).
It does not need expertise (even a layman can do).
It is relatively stable i.e. not easily changing from time to time.
Disadvantages of artificial system of classification
tends to place closely related organisms into different groups instead
of being grouped together e.g. a bat can be placed in a group of birds
instead of mammals.
Different or unrelated organisms may be
placed in the same group e.g. bats placed in a group of birds, worms
placed with snakes in the same group
The system does not provide enough information about its members.
It is difficult to incorporate additional information.
Advantages of natural system of classification
Closely related organisms are placed in the same group.
It reflects evolutionary relationships.
Unrelated organisms cannot be placed in the same group.
It makes it easy to incorporate additional information.
Disadvantages of natural system of classification
It is difficult since it considers many features.
It requires expertise i.e. more knowledge about an organism.
It is time consuming.
It is relatively unstable i.e. it changes from time to time.
It is more expensive since more data are required.
Differences between natural classification and artificial classification
(i) Considers few features in common
Considers many features in common
(ii) Does not reflect on evolutionary relationships
Reflects on evolutionary relationships
(iii) It is easy to classify
It is difficult to classify
(iv) Not time consuming
It is time consuming
(v) Does not require expertise
(vi) New information cannot be added
New information can be added.
Practical Activities of Classifying Living Things According to Artificial and Natural Classification Systems
Carry out practical activities of classifying living things according to artificial and natural classification systems
the under named organisms and keenly examine their external and
internal features:Bat, grasshopper, rat, earthworm, fish, ascaris,
cockroach, lizard, hen, hawk, and toad.
Classify the organisms using artificial classification system.
Classify the organisms using natural classification systems.
Major Groups of Living Things
Major Groups of Living Things
Mention major groups of living things
major groups of living things are the kingdoms. Previously, living
things were categorized into two main groups; plantae and animalia
kingdom. But this classification caused difficulties since some
organisms seemed to posses some of the characteristics of both groups.
For example, euglena is capable of feeding like an animal and locomote
like an animal. Therefore, it is placed in animalia kingdom. But the
same euglena has chlorophyll and it is capable of manufacturing its own
food. Therefore, it should also be placed in plantae kingdom. Such an
organism does not seem to fit exactly in animalia or plantae kingdom.
Thus, euglenas are assigned in the major group of their own.
Currently, there are five major groups (kingdoms) of living things.
Ranks of Classification
Outline ranks of classification
the millions of organisms found on earth some are more similar while
others are less similar. For example, all human beings resemble each
other more closely than they resemble with the chimpanzees. Humans have
more resemblance with chimpanzee than cats and dogs, and more like dogs
than birds.Therefore when classifying the organisms, groups are
established which are called ranks or taxa.
There are seven ranks of classification
The highest rank of classification is the kingdom. The lowest rank of classification is the species. Every known organism has particular place in each group.
Kingdom– this is the highest rank (taxon). It comprises of several related taxa. It comprises of many organisms than any other taxon.
Phylum/division– this is the second largest rank of classification. It consists of several closely related classes.
Class – members or this group have more characteristics in common than do members of division or phylum.
Order– it consists of groups that are more alike than those in a class.
Family –this is made up of groups that are more alike than those in the order. Wolves and cats are both in the order Carnivore but wolves are in the family Canidae while cats belong to the family Felidae.
Genus – it consists of very similar species but members of different species cannot breed one another.
– Species can be defined as a group of closely related organisms which
are capable of interbreeding and produce fertile offspring.
is the basic unit of scientific classification. Organisms that need to
be placed in the same species must have the following characteristics:
Must have many features in common.
Must be able to breed one another to produce fertile offspring.
Must be distinct and different from other organisms.
N.B: The term division is used by botanists instead of phylum when classifying plants or organisms related to plants.
Classification of some members of animals
Scientific naming of living organisms
scientific process of naming organisms is called nomen- clature.
Biological nomenclature is based on the binomial system (double naming
system) pioneered by the work of a Swedish naturalist Carl Linnaeus
assign scientific names to organisms so as to avoid confusion among
themselves since scientists from different countries use different
languages. The scientific names are uniform in all languages.
language is used in assigning the scientific name because it is an
official language and that this language is no longer subject to
changes; it is considered to be a dead language hence names once given
Rules of binomial nomenclature
names of organisms must be in Latin language and if the names are
derived from other languages, they must be latinized.
A scientific name of an organism has two parts, genus name and species name.
A genus name always starts with a capital letter and a species name follows with a small letter.
In typed scripts, a scientific name must be written in italics or underlined if hand written.
A specific name is sometimes accompanied with the name of the author who first described and named the organism.
When an organism is known by several names, the valid name is the one which was established after the work of Linnaeus.
Examples of scientific names
Human being:Homo sapiens
Homo is the generic name and sapiens is the specific name.
Other examples of organisms with their scientific names
Flamboyant (Christmas tree)
Tropical almond (mkungu)
Practical Activities of Grouping Organisms into their Respective Major Groups
Carryout practical activities of grouping organisms into their respective major groups
Group Organisms into their Respective Major Groups
were discovered by a Russian botanist D. I. Ivanovsky and a Dutchman
Beijerink.In 1852 Ivanovsky prepared an infectious extract from tobacco
plants that were suffering from mosaic disease. When the extract was
passed through a filter able to prevent the passage of bacteria, the
filtered fluid was still infectious. 1898 Beijerink gave the name
“virus” (in latin means, “poison”) to describe the infectious nature of
certain filtered plant fluids.
General and Distinctive Features of Viruses
Explain general and distinctive features of viruses
Characteristics of Viruses
They are the smallest living organisms ranging from 20-30nm. On average, they are about 50times smaller than bacteria.
do not have cellular structures, which mean that they lack certain
important organelles like nucleus, cytoplasm, golgi bodies, etc.
They can only reproduce inside the living cells hence they are parasitic.
They have a simple structure consisting of either DNA or RNA but not both, surrounded by a protein or lipoprotein coat.
They can be described as living or non-living.
They are highly specific to their hosts i.e. each virus recognizes only certain types of cells.
Viruses are capable of replicating themselves only when they are inside the host cell.
Viruses as living things
They possess genetic material (RNA or DNA).
They reproduce when they are in the host cell (replication).
They are capable of identifying their hosts and attack them.
They can undergo mutation (they mutate) i.e. they undergo different changes in shape.
Like other parasites, they are specific to host.
Viruses as non-living things
They can crystallize outside the host.
They are metabolically inert in isolation.
They are non-cellular i.e. they lack cell organelles.
They do not perform necessary life processes such as respiration, excretion nutrition etc.
The Structure of Viruses
Describe the structure of viruses
Generally viruses have a very simple structure consisting of the following:
RNA or DNA which may be single stranded or double stranded. They form a structure called core.
A protective coat of protein surrounding the core called capsid.
A nucleocapsid which is a combined structure of core and capsid.
Envelope – an additional layer of lipoprotein layer around the capsid.
Capsids are made up of identical repeating units known as capsomeres.
Bacteriophage is a virus that attacks and kills bacteria. Some of them have head with a tail sheath.
Advantages and Disadvantages of Viruses
Outline advantages and disadvantages of viruses
Advantages of viruses
are used in developing vaccines, for example, vaccines for measles,
polio and rubella are made from viruses that have been attenuated
Viruses are used as biological weapons to kill organisms.
are used as vectors in genetic engineering to transfer genes from one
organism to another for improving or treating the defective genes.
Bacteriophages are viruses that attack bacteria and hence they help in controlling infections and diseases.
Viruses are used as biological weapons in wars and in biological pest control.
Disadvantages of viruses
viruses cause diseases to both plants and animals. Plant disease such
tomato mosaic, cassava mosaic and tobacco mosaic; and animal diseases
e.g. measles, small pox, poliomyelitis and yellow fever are caused by
kingdom is made up of organisms known as bacteria (singular:
bacterium). They are the most ancient and smallest organisms with a
cellular structure. They are mainly single celled. Bacteria occupy many
environments such as soil, dust, water and in the bodies of plants and
bacteria are found in hot springs where temperatures are 78ºC or more.
Others can withstand very low temperatures. Some are found in very deep
cracks in the ocean floor, at very high temperatures, about 360ºC
General and Distinctive Features of the Kingdom Monera
Explain general and distinctive features of the kingdom monera
General characteristics of the kingdom monera
They are mainly unicellular and very small.
They are all prokaryotic (nucleus not bound by membrane)
They reproduce by binary fission.
Some members of the kingdom are autotrophs while others are heterotrophs
They have cell wall made up of protein material and sometimes lipids.
bacteria form spores during adverse conditions i.e. extreme conditions
e.g. high or low temperatures, drought etc. The spores allow them to
survive as they have very thick resistant walls.
Some are aerobes while others are anaerobes.
genetic material (DNA) is scattered in the cytoplasm and they lack
internal membrane bound organelles such as mitochondria, chloroplasts,
golgi bodies etc.
Structures of the Representative Organisms of the Kingdom Monera
Describe structures of the representative organisms of the kingdom monera
General structure of the bacteria
have strong and rigid cell walls due to the presence of murein. The
wall prevents the cell from bursting when it absorbs much water (as a
result of osmosis).
Bacterial cells are bounded by partially permeable membranes.
possess capsules which are slimy or gummy.They have flagella which aid
motility of the bacteria. Motile bacteria can move in response to a
certain stimulus i.e. tactic movement. Flagella can easily be seen by
They have small self replicating circle of extra DNA called a plasmid.
General structure of bacterium
Forms of bacteria
Bacterial shape is an important aid to classification. There are four main shapes
Coccus (plural: cocci)
They are spherical in shape and can be of the following types.
Micrococcus – exist singly. They cause sore throat.
Diplococci – this type of bacteria exist in pairs. The pneumococci (Diplococcuspneumoniae) are the only members. They cause pneumonia.
– this type of bacteria stick together and form a chain. Most of them
infect upper respiratory surface and cause diseases e.g. sore throat.
Staphylococci – These bacteria form a grape like bunch. They cause boils, pneumonia, food poisoning and other diseases.
Bacilli (singular: bacillus)
These are rod shaped bacteria. They can be:
Single rods, for example, Escherichiacoli commonly living in the gut and Salmonella typhi which cause typhoid fever.
Rods in chain, for example, Azotobacter, a nitrogen-fixing bacteria, and Bacillus anthracis which cause the disease anthrax.
Bacilli with endospores showing various positions, shapes and sizes of spores. They can be:
Central, not swollen e.g. Bacillus anthracis causes anthrax
Spherical spore, terminal swollen e.g. Clostridium tetani causes tetanus
Sub-terminal, swollen e.g. Clostridium botulism causes botulism.Spores may also be central
Spirilla (singular: spirillum)
These are spiral-shaped bacteria e.g. Treponemapallidum which causes syphilis
These are comma shaped bacteria, for example Vibrio cholerae.
The Advantages and Disadvantages of the Kingdom Monera
Outline the advantages and disadvantages of the kingdom monera
Economic Importance of Bacteria
In Agriculture, the bacteria are mostly important for following reasons
cannot trap nitrogen from the atmosphere but bacteria can fix nitrogen
and change it into nitrogenous compounds. The phenomenon is called
nitrogen fixation. The bacteria, which fix atmospheric nitrogen, are
called nitrogen-fixing bacteria. Some of the nitrogen fixing bacteria
are found freely in soil are called free-living bacteria, eg.
Clostridium and Azotobacter. Some of them are found in root nodules
making association with leguminous plants called symbiotic bacteria, eg.
Nitrification:Some bacteria convert
ammonium compounds into nitrates in the soil. The process is called
nitrification. The bacteria that take part in this process are called
nitrifying bacteria, eg. Nitrobacter and Nitrosomonas. Nitrosomonas
bacteria utilize proteins of dead bodies and convert it into amino
acids. These amino acids are converted into ammonia by some bacteria.
The process is called ammonification and the bacteria involve in the
process are called ammonifying bacteria. Then the ammonia reacts with
CO2 and H2O and gives ammonium carbonate which is absorbed by plants.
Bacteria decompose dead bodies. They convert complex organic compounds into simple inorganic compounds. Therefore they’re called natural scavengers.
Bacteria make the milk sour and produce flavor. They are responsible for coagulation of milk. E.g. Lacto bacillus.
Bacteria convert sugary substances into alcohol, acids, acetones; etc the process is called fermentation.
Bacteria also help to produce different types of enzymes like Amylase secreted from Bacillus, Protease from Bacillus, Streptokinase from Streptomyces.
Bacteria are useful for vitamin production like Vitamin B (Cabalmin) is secreted from Pseudomonas, Vitamin B (Riboflavin) is secreted from Clostridium.
They are important for antibiotic production like Terramycin from Streptomyces rimosus, Streptomycin from S. griseus, Neomycin from S. fradiae.
They are also important to produce hydrogen commercially. During the process they ferment carbohydrate and hydrogen gas is produced.
Bacteria decompose waste products.
Disadvantage of Bacteria
of the species cause food poisoning. They secret some toxic chemical
substances on out food stuff which cause food poisoning, eg
Staphylococcus and Clostridium.
Some are responsible for human
diseases: Cholera: Vibrio cholera, Pneumonia: Staphylococcus pneumoniae,
Diarrohea: Escherechia coli, Tuberclosis: Mycobacterium tuberclosis
Leprosy: M. leprae, Meningitis: Nisseria meningitides.
bacteria are responsible for plant diseases. Red stripe in sugarcane,
Leaf streak in rice, black rot in cabbage and yellow rot in wheat are
caused by Xanthomonas and Pseudomonas.
The Characteristics of Pathogenic and Non-pathogenic Bacteria
Outline the characteristics of pathogenic and non-pathogenic bacteria
Pathogenic bacteriaare bacteria that can cause infection. This article deals with human pathogenic bacteria.
most bacteria are harmless or often beneficial, several are pathogenic.
One of the bacterial diseases with the highest disease burden is
tuberculosis, caused by the bacteriumMycobacterium tuberculosis,
which kills about 2 million people a year, mostly in sub-Saharan
Africa. Pathogenic bacteria contribute to other globally important
diseases, such as pneumonia, which can be caused by bacteria such asStreptococcusandPseudomonas, and foodborne illnesses, which can be caused by bacteria such asShigella,Campylobacter, andSalmonella.
Pathogenic bacteria also cause infections such as tetanus, typhoid
fever,diphtheria,syphilis, and leprosy. Pathogenic bacteria are also the
cause of high infant mortality rates in developing countries.
those that do not cause disease, harm or death to another organism and
is usually used to describe bacteria.It describes a property of a
bacterium – its ability to cause disease. Most bacteria are
nonpathogenic. It can describe the presence of non-disease causing
bacteria that normally reside on the surface of vertebrates and
invertebrates as commensals. Some nonpathogenic microorganisms are
commensals on and inside the body of animals and are called microbiota.
Some of these same nonpathogenic microorganisms have the potential of
causing disease, or being pathogenic if they enter the body, multiply
and cause symptoms of infection.
individuals are especially vulnerable to bacteria that are typically
nonpathogenic but because of a compromised immune system, disease occurs
when these bacteria gain access to the body’s interior. Genes have been
identified that predispose disease and infection with nonpathogenic
bacteria by a small number of persons.Nonpathogenic colistrains normally
found in the gastrointestinal tract have the ability to stimulate the
immune response in humans, though further studies are needed to
determine clinical applications.
General and Distinctive Features of the Kingdom Protoctista
Explain general and distinctive features of the kingdom protoctista
Kingdom comprises of unicellular and simple multicellular organisms
whose cells have organized nucleus and membrane bound organelles. It
includes the algae and protozoa.
have chlorophyll hence make their own food through the process of
photosynthesis.Protozoa are heterotrophic taking in ready-made food.
organisms, which are included in this Kingdom are red algae, Brown
algae, Amoeba, Euglena, plasmodium, trypanosome and paramecium.
General features of Kingdom Protoctista
Some are autotrophs, for example Euglena while others are multicellular.
They are all eukaryotes with most of them having locomotery structure.
Most of them live in moist places or in water.
Most are unicellular eukaryotes
They reproduce by binary fission
Phyla of the Kingdom Protoctista
Mention phyla of the kingdom protoctista
The phyla of kingdom protoctists include the following:
Euglenophyta e.g. Euglena
Rhizopodia e.g. Amoeba
Zoomastigma e.g. Trypanosoma
Apicomplexa e.g. Plasmodium
Oomycota e.g. White root
Chlorophyta e.g. Spyrogyra
Cilliaphora e.g. Paramecium
Rhodophyta e.g. Red algae
Structure of Amoeba and Paramecium
Describe structure of amoeba and paramecium
Amoeba belong to phylum Rhizopoda, organisms with the following extra features:
They are eukaryotes
They move using pseudopodia
Pseudopodia are projection of the cytoplasm that extend and pull the amoeba forward or engulf food particles.
The Advantages and Disadvantages of Amoeba, Euglena Paramecium and Plasmodiu
Explain the advantages and disadvantages of amoeba, euglena paramecium and plasmodium
Advantages of Paramecium:Are eaten by small water animals
Disadvantages of Paramecium:Causes diseases of bulanterdium eoli destroying the lining of intestines
has two contractile vacuoles and each is associated with permanent
system of collecting channels, which empty, into the main vacuole.
Feeding:Paramecium feed on bacteria. These are obtained from the surrounding water by the beating of the cilia-lining o the oral grove.
reproduces both asexually and sexually. The asexual method is more
common and it is binary fission. Sexual method is called conjugation.
Movementin paramecium is caused by cilia beating. This movement is called cilliary movement.