BIO 101 – GENERAL BIOLOGY I

BIOLOGY: The study of life or more appropriately the study of living organisms (living things).

WHAT IS A LIVING THING?

A living thing is anything that is capable of reproducing itself and carryout life processes such as
respiration, movement, eat and carryout metabolic processes (nutrition), response to stimuli,
growth, excretion and finally (eventually) die. To carry out these processes a living thing
comprises units and structures that make up the body just as individual a toms combine together
to form matter or substance. The basic unit of life is the cell. Before we discuss the cell, let us
discuss these processes that characterize living things.

RESPIRATION: Respiration is more than exchange of gases but involves the metabolism of
energy sources (food) and the use of these for essential life processes.

MOVEMENT: Movement can be in the form of locomotion as in the case in animals or responses
to environmental stimuli such as tropic (tropism) and tactile (taxism) such as we have in plants.

RESPONSE TO STIMULI: All living things respond to environmental factors such as light,
temperature, water, gravity etc.

GROWTH: All living things are capable of physical increase in size. Growth is due to increases in
the size and number of cells.

EXCRETION: From the smallest of all living things to the largest, all can dispose of unwanted
products from their body.

REPRODUCTION: All living thing can reproduce their kind either vegetative (asexual) or
through sexual means.

NUTRITION: They can take in solid substance, digest or accumulate them for growth.

CELL

A cell is the smallest unit that can carry out all life processes. An organism can be made up of one
or more cells. An organism with a single cell is called a unicellular organism while those with
two or more cells are called multicellular organisms. Examples of unicellular organism are
paramecium, amoeba, euglena etc. The simplest of these are bacterial cells. There are also simple
multicellular organism such as hydra and of course complex o nes such as higher plants and
animals. In human for examples there are different forms (types) of cells and nu mber up to
trillion of cells (10 12).

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BASIC STRUCTURE OF A CELL.

Assignment –Prokaryote cell – draw and state features

S/N Prokaryotic Eukaryotic

Kingdoms Bacteria and Archaea Kingdoms Protista, Plantae. Animalia, Fungi

1 Size – about 5um (usually < 10um) >10um

2 Always unicellular Mostly multicellular except some Protists.

3 No organized or membrane enclosed Has membrane bound nucleus

nucleus

4 Single chromosomes in cytoplasm 2 or more in nucleus, arranged in pairs called

homologues (homologous pairs)

5 70S ribosome (50S + 30S) 80s ribosome (60S + 40S)

6 No cytoskeleton Always with cytoskeleton.

7 Division is by binary fission Cell division is by meiosis and mitosis

There are two classes of cells – prokaryotic and eukaryotic. Irrespective of whether microbes,
plants or animals, all are made up of the same basic materials.

A typical cell is made up of;

- An outer covering
- The cytoplasm and
- A nucleus (A nucleoid region in prokaryotes since they do not possess an organized
nucleus)

THE OUTER COVERING

The outer covering of cells of different organisms is made up of different materials. They can be
a cell wall or a membrane.

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Cell wall: Cellulose cell wall is a characteristic of plant cells. The cell wall can be made of
carbohydrates such as cellulose pectin, hemicelluloses and wax. This gives a rigid shape to plant
cell. The cell wall of Fungi is made up of chitin, a substance similar to exoskeleton of insects. This
is why it smells like roast insect when put in fire. Bacteria have cell wall of peptidoglycan while
Archaea cell wall is made up of complex lipids that partly accounts for their ability to survive in
extreme conditions.

Plasma membrane is more typical of animal cell although may be present in the inner wall of
plant cell. This extremely thing membrane is variously referred to as plasmalemma, cell
membrane or more commonly plasma membrane.

The plasma membrane is a three- layered structure made up of two dark layers sandwiching a
translucent inner layer. These layers may be made of phospholipids glycoprotein or glycolipids.

It is good to note that cell organelles are also surrounded by plasma membrane. The nucleus is
surrounded by nuclear membrane. The main functions of the outer covering are to give shape
and distinction to each cell and organelle. It also protects the organelles and allows absorption of
useful material and ensure the ejection of unwanted materials.

CYTOPLASM

The cytoplasm is made up of fluid (cytosol – water and dissolved molecules such as amino acids )
in which the organelles are suspended. The cytoplasm can be seen streaming with the various
organelles in constant but random motion. There are other inclusions such as stored food and
secretory substances. The cytoplasmic organelles perform different functions as already seen.

THE NUCLEUS

The nucleus controls all the activities of the cell because it holds most of the genetic materials
(the nuclear genome) while other genetic materials are contained in the mitochondria and
plastids (in plants). The genetic materials carried in the cytoplasmic organelles are usually
transmitted through the egg (maternal inheritance).

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State differences between plant and animals cell.

SN PLANTS ANIMALS

1 Relatively large smaller in size

2 Large central vacuoles None

3 Presence of plastids No plastids

4 Enclosed by cellulose cell wall in addition Enclosed by plasma membrane

to the plasma membrane

5 No lysosome Lysosomes for digestion often present

6 Nucleus located in one side of cell Usually located in the center of the cell

7 Glyoxysomes may be present Glyoxysomes absent

8 Plasmodesmata present Plasmodesmata usually absent

9 Reserve food as starch Reserve food as glycogen

10 Plant cell can synthesize all the amino Animals cannot synthesize all the AA and co –
acids and co-enzymes required. enzymes and vitamins required

11 No asters at spindle formation Asters are formed at the pole during spindle
formation.

12 Cytokinesis achieved by cell plate method Cytokinesis achieved by constriction or

furrowing method

13 Cell wall prevent cell bursting when in Animal cells lacking contractile vacuole often
hypotonic solution burst when placed in hypotonic solution

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Draw a plant /animal cell and label its parts.

What are plastids? Organelle in plants and algae that are used in the synthesis and storage of
various products.

- Chloroplasts (Green)– photosynthesis

- Leucoplasts (Colourless)– storage of starch, proteins and lipids
- Chromoplasts (Coloured)– plastids for pigment formation as in corolla of flowers

Prokaryotic cell

Prokaryotic cells each prokaryotic cell comprises a plasma membrane surrounded by a rigid
cell wall of peptidoglycans in Eubacteria but special lipids in Archaebacteria. The cell wall
may also be covered with a capsule which provides additional protection to the cell.

The cytoplasm lack membrane covered organelles, with no organized nucleus but the
genetics material, usually a circular chromosome (refer to as naked DNA) found in the
nucleoid region. There are also genetic materials called plasmids, usually circular and rarely
linear. Many bacteria also have flagellae which they use in movement, and several thread –
like projections called pili (sing. pilus)

Diagram

Prokaryotic cell

CELL MEMBRANE: Functions in transporting substances in and out of the cell and in the
breaking down of molecules.

CELL WALL: Provides cellular integrity and enables structural strength to cell thus the cell is
rigid as in plant cell.

CAPSULE: This jelly – like substance protects the cell wall from breaking down when
exposed to chemicals and other environmental conditions

NUCLEIOD: This region holds the simple, circular genetic material or chromosomes – a
naked DNA

RIBOSOMES: Are located in the cytoplasm along with the RNA thus rate of protein synthesis
is faster in bacterial cell as transcription and translation occur simultaneously.

VESICLES: Cyanobacteria contains these and are responsible for photosynthesis

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FLAGELLUM: These whip-like structure functions in movement. The flagellum rotates like a
propeller thus causing the cell to move.

PILI – This are also projections used by the bacteria in holding fast (adhesion) to other cell or
objects they are also used in transferring genetic material from cell to cell during
conjugation.

Eukaryotic Cell Organelles

Unlike prokaryotes, organelles in Eukaryotes are enclosed in membrane.

The main organelles in cell are the nucleus, mitochondrion, endoplasmic reticulum (RER and
SER), ribosomes, (Golgi apparatus, vesicles, lysosomes, ribosomes, centrioles, cytoskeleton
etc.

THE NUCLEUS: This is the largest cell organelle in most living things except in plants in
which the central vacuole occupy most part of the cell. It is surrounded by the nuclear
membrane. The nucleus contains the genetic materials. The nucleus centre of the cell because
it holds the genetic material as well as a nucleolus which is involved in making ribosome and
processing the messenger RNA (mRNA)

ENDOPLASMIC RETICULUM: There are two types – Rough endoplasmic reticulum (RER)
and Smooth endoplasmic reticulum (SER). The reticulum is made up of extensively folded
intracellular membrane that is continuous with the nuclear membrane.

RER; The RER is different from SER in that it is associated with ribosomes. It is concern with
protein synthesis

SER: The SER is responsible for the production of enzymes It is responsible for the storage of
calcium which it releases to the cytoplasm when required. This is necessary for muscle
contraction.

GOLGI APPARATUS: I responsible for transport and modifications of problems and other
biomolecules to specific locations within the cell. This sorting function of the Golgi apparatus
makes it to be regarded as the cell’s packing centre.

Mitochondria contains enzymes and provide machinery for aetrobic respiration and
oxidative phosphorylation. It generates the ATP which is responsible for energy charges in
cell. As such the mitochondria are regarded as the powerhouse of the cell.

RIBOSOME: The ribosome is responsible for protein synthesis. It is associated with the RER
giving if the granular appearance thus the name rough.

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 PLASTIDS: Plastids occur in plants and algae and are of various forms they include
chloroplasts, chromoplasts, elaioplast and leucoplasts. This organelle serves as energy
converter and sorer in green plants and algae. They are self replicating and having their own
genetic material which direct its functions.

LYSOSOMES: The lysosomes contain enzymes for digesting ingested materials and damaged
tissues acting as a recycling center of the cell.

Cytosol – all fluid liquid + dissolved substances. + the cytoskeleton (cytoskeleton – network
of tubes fibers and filament that help in maintaining cell shape, hold the organelles in
position and cause movement of cellular materials/organelles.

Plant and Animal cell

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HISTORY OF THE CELL KNOWLEDGE

The understanding of biology has developed side by side with the invention and the
development of the microscope especially since the 17 th century. With the microscope available,
men began to examine both living and dead biological tissues. We can conclude that modern cell
biology developed with microscope.
The word “cell” (which means hollow space) was coined by Robert Hooke 1635 – 1703) after he
examined thin slice cut from a piece of dried cork under the compound microscope.
He described cell as a hone comb of chambers. The chambers that Hoo ke saw are now known to
be empty spaces (Hollow) left behind after the living portion of the cell had disintegrated. The
first person, however, to examine a free living cells was Anton van Leewenhoek (1632 – 1723).
Leewenhoek observed microbes in water collected from tubes inserted into the soil during
rainfall. Some of the microbe he draw included numerous bacteria such as bacilli, coca, sprilla
and other monera, protozoa, rotifers and hydra. He was the first to describe the sperm cells of
man, dogs, rabbits, fish, frog, and insects. In 1838, Theodor Schwann determined that animals
consists of cells while M. J. Schleiden said that plants are also made up of cells Schwann and
Schleiden also discovered that cells contain a nucleus. From their observation, they concluded
that all organisms are made up of cells.
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THE CELL THEORY.
Today the cell theory is as follow
1. The cell is the fundamental unit of life that function in living things (nothing less than
a cell is living)
2. All organisms are made up of one or more cells
3. Cells arise from cells through cell division. This means that cells arise from pre-
existing cells through cell division, i.e. no new cells originate spontaneously today.
4. Cell contain genetic materials which are passed to daughter cells during cell division
5. All cells are essentially the same in chemical composition
6. Energy flow occurs within cells

ORGANISATION OF LIVING THINGS

Subatomic - electrons, protons, neutrons

Atomic - O2, H2 C, N, S

Simple molecules - H20, CO2, NH3,

Macromolecule - CHO, DNA, RNA

Enzymes and other precellular
Biomolecules

BIOMOLECULES

amino acids starch DNA, RNA

peptides

polypeptides

protein

As shown in the tables of biological organization, it is evident that nature is arranged in definite
and logical order. The levels from the subatomic particles electrons, protons and neutron up to
complex molecules (bio – molecules) are not living things. However, they are composed of these
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elements. In other words what becomes the living entity comes from non-living thing. Just as
atoms are arranged to become complex molecules, cells become the building block of living
things. The most primitive organism the bacterium, is made up of functional grouping of
biomolecules. At every level of organization, the components that make up each are organized to
function together such that each member depends on one another. There is no member of a
functional grouping that is non-essential. Think about these:
What happen if the mitochondria or Golgi apparatus or plastids are absent in a cell?
What will happen if the artery or vein malfunction or absent in the circulatory system?
What will happen if the brain is absent or damaged in the nervous system or there is a breakage
in the CNS?
What will happen if all the animals in a population are females or males?
From these questions it is clear that nature is perfectly organized another thing of note, apart
from the fact that the complexity of organization increases with each level (tissue is more
complex than the cell, organ that tissues no cell no tissue etc) there are emergent properties at
each level, that is a new role that the lower level cannot perform.

CELL DIVERSITY
Cell diversity refers to the differences and variations in cells size, sh ape, volume, structure and
complexity.
CELL SIZE: cells show a wide range in size. The cells of prokaryotes may be as 1 – 10 um. In
general, eukaryotes have larger cell size 10 – 100um. In animals, variation in cells vary from
animal to animal and from tissue to tissue. In man for example, the egg cell is about 1000um (1
cm), such that it can be seen without the aid of a microscope. In many animals especially the egg
layers such as reptiles, amphibians and aves (birds), egg size can be very large. The largest
known cell is the egg of the ostrich. Cells length also vary and can be very long in nerve cells of
animals and schlerechyma cells of plants, some even up to a meter! The size of any cell depends
on its function.
CELL SHAPE: The shape of cells is determined by its function. Generally cells are ovoid to
spherical. However, some cells can be rod shaped as in bacilli species of bacteria, spherical like
cocci bacteria and most cells, oval as in avian birds or linear with varied modifications such as in
nerve cells, fiber cells, spiral as in Sprilla. Many cells may be flagellated, ciliated etc.
Some cells change shape with age and circumstances of function (i.e. the function they need to
perform at a particular time).
CELL VOLUME: While cell size in terms of two dimensional shape varies due to varied functions,
there is limit to the volume of body cells. There is little variations in the cells of multicellular
organisms. The law of constant volume shows that there is limit to which cell can grow for it to
be able to function and communicate with other cells. When size of an organism vary largely, cell
volume are nearly the same in all organisms but the number o f cells in each organism vary
largely, for example, the volume of cell in a mouse is not different largely from that of a cattle or
hippo but the number is what makes the differences. The volume of the cells in a boy is not
smaller than that of a full grown adult but the number varies largely.
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CELL NUMBER: The number of cells in an organism varies from ONE in unicellular organism
(amoeba, paramecium) to trillions in animals as explained above, the number also varies with
the organism’s size. The number of cells in pea plant is different from mahogany. The number of
cells in a seedling is smaller than that of a full-grown plant.
CELL ORGANIZATION: The organization of cells varies with the function of the cell and the
complexity of the organism bearing it. For example, the cell of a bacterium is simpler, with only
one circular chromosome while eukaryotic cells have a nucleus with two or more chromosomes.
CELL TYPE AND FUNCTION
Cell type is a classification used to distinguish between morphologically distinct cell forms
within a species. Although cells within a species are all of the same genotype, they may be in
different forms with each of the cells taking the form in which it can function effectively even in
unicellular organisms
The cellular form can change form time to time. Some bacteria may form endospore in reaction
to unfavorable condition protozoa such as Amoeba may change not only their shapes but may
unite with other organism to form a conglomerate.
In multicellular organisms, animals as well as plants, the cells take on different forms or types.
The changing of cell of the same type to different forms to carry out different functions during
the process of development is known as differentiation.
An undifferentiated cell that is capable of developing into different types or forms is known as
stem cell in animals. In plants they are called meristematic cell.
Meristematic cells can be found in growing points such as root tip and apical bud of plant. At
these points, all the cells are alike. Stem cells /meristematic cells develop into different cell types
due to differential regulation of the genes of the cells.

CELL TYPE IN MAN

In man, as well as other animals and plants, cells are generally divided into two fundamental
types – the somatic cells and the germ cells
BODY CELLS
Body cells are called somatic cells with diploid number of chromosomes in contras t with sex
(germ) cells or gametes which are haploid.

CELL DIVISION

The cell Cycle

The cell cycle is the period between two mitotic divisions. The time from the end of one mitotic division
to the beginning of the next is known as the interphase. As shown in figure, the time for mitosis is a brief
period usually about 4.1% of total period of the cycle. In brief the cell cycle comprises the interphase and
mitosis

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INTERPHASE

G1 phase: This is the period of RNA and protein synthesis. The cells grow in size.

As shown in figure, the interphase is divided into three phases –G1, S and G2.

S phases: This is the period of DNA synthesis. The commencement of DNA synthesis marks the
beginning of the S phase. By the end of the S phase the DNA complement in double, i.e. move from 2n to
4n.

G2 phase: This is the period between the S phase (synthesis of DNA) and the commencement of mitosis.
It is the preparatory phase for mitosis to begin

MITOSIS: Mitosis describes the process of cell multiplication in which a single cell divides into two to
form two identical daughter cells as illustrated in the figure below. 2

Figure: In mitosis, one cell divides to become two identical daughter cells 2 n
2
n
The process occurs in somatic cells (autosomes) and comprises two processes – karyokinesis and n
cytokinesis. Although the process of nuclear division is continuous, it is divided into four phases for
convenience of description and study as follow;

- Prophase
- Metaphase
- Anaphase
- Telophase

Prophase: The chromosomes condense and are at first seen as thin threads at early prophase. As the
chromosomes condense and continue to shorten, it can be seen clearly under a light microscope and by
late prophase, individual chromosomes can be seen as two stands joined at the centromere.

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Metaphase: At metaphase, the chromosomes move towards the centre (equator) of the cell the
kinetochore fibres pull on the centromere and cause the chromosomes to arrange and remain on the
metaphase plate in a defined order. The chromosomes appear very clearly and can be studied. The cell
begins to acquire water and the chromosomes may start to lengthen again.

Anaphase: The spindle fibres pull on the kinetochores and pull sister chromatids (one strand of
chromosomes) towards opposite directions. The shape of the chromosomes at this stage depends on the
position of the centromere on the chromosome. The shape may be V for metacentric chromosomes, J for
sub-metacentric chromosomes and I for telocentric chromosomes. As the cells acquire more water, the
chromosomes lengthen.

Telophase: Each set of separated chromatids (now chromosomes) is assembled at the poles as new set of
chromosomes. The spindle disappears and the nuclear membrane reappears.

Cytokinessis: Cytokinesis refers to the dividing of the cytoplasm into two, thus causing each side of the
cell become two independent cells. In animal cells, it is achieved by a cleavage at the middle of the cell
until the cells is ‘cut’ into two.

In plant cell, it is achieved by the formation of cell plate at the middle of the cell which leads to the
dividing of the cell into two daughter cells.

CLASSIFICATION OF LIVING THING

The science that deals with the classification and having of living things is known as taxonomy.
Classification is the process of arranging organisms in groups. This is done to characterize the
millions of living things for universally acceptable group for identification. Before we go into the
reasons for classification, let us see attempts made to classify identify and name living
organisms.

History of Taxonomy (Nomenclature)

From medical times, man had looked at the vast diversity of mater and tries to group and name
them. For example Aristotle (384-322 BC) in his work used the word “substance” “species” and
genus” in classifying beings. In his system, a man is primarily a person – John, and then John is
secondly a man. A species may be many but members belonging to the same type.

As knowledge increases, and man explore all the continents, subcontine nt and the islands, more
and more living organisms were discovered and the need to categories/group them into distinct
taxon Swiss Prof. Conrad Von Gesner (1516 -1565)made a computation of known living things.
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In fact with the invention of the microscope, more organisms were discovered. The works of
Fabricus (1537 – 1619), Petrus Servennus (1580 – 1656), Wilhem Harvey (1578 – 1657) and
Edward Tyson (1649 – 1708) provided further impetus to the science of taxonomy.

The real science of Taxonomy as known today began with the works of Carolus Linnaeus (1707 –
1778)

Linnaeus actually introduced what is now known as the binomial nomenclature. In his system,
he classified living things into plants two kingdoms namely plants and animals. He was unaware
of the microorganisms which now belong to the bacteria (Monera in the five Kingdom
classification or Archaea and Eubacteria in the six Kingdoms classification), as well as many
Protists.

The table below shows the various attempts at the classification of living thing s.

Advantages of classification

1. Grouping of animals enable easy identification since a particular group will share some
common characters.
2. It affords easy and systematic study of organisms Animals within and between group(s)
can be compared or contrasted.
3. Differences between different taxonomic groups can be quickly seen
4. as selection Classifications remove confusion due to use of common names for instance
wormwood are different in different places. Robins in America is different from what is
known as Robin in Europe
5. Classification makes sampling of living things simpler of a few member in a group can
suffice to represent all members of the group.
6. The evolutionary relationship among living things can also be easily seen.

Classification systems

Artificial Natural
Based on use of one or a few based on several characters
Characters thus not show the such as anatomy, morphology,
Relationship among living things biochemistry, DNA, and
molecular studies.
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 The two Kingdom system.
Carolus Linnaeus (1707 – 1778) simply classified living things into the two kingdoms of
I. Kingdom of plants
II. Kingdom of animals

In this system fungi and all green plants are in one kingdom, plantae. All other living things were
regarded as belonging to the kingdom – animalia.

Five Kingdom system

The five kingdoms were proposed by R.H. Whittaker in 1969. The five kingdoms are

i. Monera
ii. Protoctista (Protista)
iii. Fungi
iv. Plantae
v. Animalia

This system considered three factors

a. Cell structure
b. Body structure and
c. Mode of nutrition

Monera – The organism here are the bacteria. Monerans are microscopic with simple cells
without organelles with rigid outer covering (cell wall made up of peptidoglycan)

Protista- the organisms are microscopic, unicellular eukaryotic plant like and animal – like
organisms

Examples: Chlamydomonas, Amoeba, Paramecium

Fungi- These are mainly multicellular eukaryotic organisms. They lack chlorophyll and thus are
heterotrophis. The body is made up of stem-like hyphae and a head called sporagiophore. There
are two types of fungi – unicellular fungi generally referred to as yeasts e.g. Saccharomyces,
Candida, and multicellular fungi generally referred to as moulds e.g. Aspergillus, Mushrooms etc.

Plantae: Plants are multicellular eukaryotic organisms. The cell wall- cellulose they possess
green plastids containing chlorophylls and can thus manufacture their own food. They are
autotrophs. Plants are generally divided into four groups namely – non – tracheophytes,
comprising three divisions, seedless tracheophytes comprising four divisions, naked seed plants
called gymnosperms and flowering plants also known as angiosperms.

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Animalia

Multicellular, eukaryotic heterotrophs.

The cell are made up of plasma membrane

Example_

- Invertebrates –without backbone

- Vertebrates- with backbone

The six kingdom classification.

The six kingdoms classification was proposed by Cavellier and Smith in 1998 as seen the table
above, the six kingdoms are the two kingdoms of bacteria- Archaebacteria and Eubacteria
(chromesta) as well as the Kingdoms of Protista, Fungi, Plantae and Animalia.

Generally, the popular classification is based on the three domains and six kingdoms
classifications follow.

Three domains:

Archaebacteria (Archaea) – Kingdom Archaea

Eubacteria – Kingdom Bacteria

Eukarya – Kingdoms Protista, Fungi, Plantae and Animalia.

The six Kingdoms are:

Archaea

Eubacteria

Protista

Fungi

Plantae and

Animalia.

The first two, archaea and bacteria from the kingdom monera in the five kingdom classification
of Whittaker et al., 1969.

The characteristics of the various Kingdoms are as follow.

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Archaea: These are bacterium like organisms that live mainly in areas of extreme conditions.
Extremophiles are put in three groups – methanogens, halophiles and thermophiles. They are
different from the true bacteria in their cell wall which is made up of uncommon lipids rather
than peptidoglycans. They are unicellular prokaryotes with very simple cells without membrane
enclosed organelles. They can be autotrophs or heterotrophs. E.g. Methanothermus,
Methanoaldococcus.

Eubacteria: They are regarded as the true bacteria . their cell wall is made up of peptidogycans.
They are prokaryotes with simple cellular form. They can be autotrophic or heterotrophic.
Unlike the Archaea, some are motile e.g. E. coli, Staphylococcus, Streptococcus.

Protista: The Protists are mainly unicellular, some are simple mullicellular eukaryotic
organisms.

The Protists are of three types;

Autotrophic, plant – like e.g. Dinoflagellates, diatoms, green, red, brown algae

Hetetotrophic decomposers, fungi – like e.g. water moulds, slime mould

Heterotrophic consumers, Animal – like e.g. Amoeba, paramecium

Fungi: Fungi can be unicellular e.g. (Yeasts) or multicellular (moulds). They are all eukaryotes
and are mainly decomposers (hererotrotrophs). Reprduction is essentially by means of spores.

Hierarchical order.

The grouping of organism into hierarchical order was initiated by Carl (Carolus) Linnaeus. The
hierarchy are as follow:

Domain (Empires) (introduced By C. Woese 1990)

Kingdoms

Phylum

Class

Order

Family

Genus and species

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Species

A species is a grouping of organisms who can interbreed to produce fertile offspring. In the
hierarchy group of living things, the species is the lowest and comprises most closely related
organisms. Closely related species are put in the same Genus. The extent of relationship
decreases through the ranks with the domain comprising the least related organisms.

Naming of organisms – (nomenclature) the represent system of naming organism is called the
binominal nomenclature first introduced by Linnaeus.

Binominal nomenclature refers to the system of naming an organism with two part names –
the genus name (generic name) and the species name (the specific epithet.

Trinomial nomenclature: This is a three part name, that is, an addition of another descriptive
name to the binominal nomenclature to indicate a particular organism below the rank of a
species such as a subspecies or a cultivar or varieties of a species.

Writing a Binominal Name:

How to write name of an organism.

The name of an organism starts with the genus name (just like a surname/family name) then
followed by the species name (specific name/specific epithet)

Examples

Domestic dog: Canis familiaris

Rice Oryza sativa

In these two examples, the word Canis is the generic name and should start with a capital letter (
upper case). Canis not canis.

Also, familaris is the specific epithet and starts with low case letter.

A scientific name must be underlined when written like this Canis familiaris NOT Canis familiaris
that is each word underlined separately.

In printed, it is in italics.

Example of trinomial nomenclature

Urginea indica ssp. indica

Urginea indica ssp. augustifolia

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Urginea indica ssp. tenuifolia

ssp. = subspecies

cv. = cultivar or cultivated variety

var. = variety

Note: A cultivar or variety name is not written in italics but put between quotation marks

Authority citation

The person who first published the name of an organism variety is as the author. When writing
the name of an organism in a formal writing, it is expected that the author be written too.

The author’s name is always written in abbreviated form. Example are

L. for Carolus Linnaeus

Scop. For G.A. Scopoli

Lam. J. P Lamarce two different authors bear the same surname, an additional letter (s) are
included to differentiate between/among them.

Examples

William Hooker – as Hook.

J. D. Hooker ( son of William Hooker) Hook . F.

There are other cases where two different authors describe an organism. Based on the nature of
correction and relative time of valid publication of the names, authors name may be followed by
different symbols or abbreviations

Examples

1. et when two or more authors publish a new name or proposed a new name
2. ex when the first author proposed a name and did not publish it. Then another author
publishes the name.
3. in when the first author publish the name in a publication of another
4. Emend when a correction is made by an author. In the diagnosis/
Circumscription of a species without altering the types symbol
5. ( ) A parenthesis is used to show that a new author has made a change in
the name of a species
6. { } to indicate a prostrating author, his name is put within a square
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 Bracket. A prostrating author is one of that validly publish a
Name before 1753.

HEREDITY AND EVOLUTION

All living things can pass traits to their offspring and thus carry on the characters of the parents
generations after generations with little or no changes. This passing of traits from parent to
offspring is known as heredity. For example a dog will always bear baby dogs or puppies, man
to babies. However, one can always tell one puppy from the other even though they are born by
same parents. Twins can show striking differences even though they are born by the same
parents at the same time. This differences in members of the same species from the same
parents is called variation.
In asexual reproduction, all offspring look alike and any slight difference can only be due to the
effect of the environment. In sexually reproducing species, offspring show much variation due
to genetic mix – up during meiosis as well as the independent assortment of gametes during
fertilization. As such, each individual member is what it is because of what it inherits from both
parents. This traits are carried in biomolecules called deoxyribonucleic acids or DNA. This
molecule is in a structure called chromosomes. Bacteria and Archaea usually contain one
(usually) circular chromosome and thus do not undergo meiosis. Reproduction is by binary
fission. Therefore all daughter cells of the same bacterium cell remain alike for several
generations unless there is change in the DNA. This change is called mutation. All of what an
organism will look alike, that is the phenotype is determined mainly by its genetic makeup or
genotype as influenced slightly by the environment. Other changes can only be due to mutation
which is a permanent change in DNA structure of an organisms. Most mutations are always
detrimental to the bearer of the mutation called a mutant.

The Chromosome: The chromosome is the structure that holds the genetic material called the
DNA. In prokaryotes, it is contained in the nucleoid region of the cytoplasm. Other genetic
materials called plasmids also carry biological information that can be transferred from
generation to generation and from one bacterium cell to another. Both the chromosome and the
plasmids are important in passing biological information in form of traits to other bacterium/
bacteria (horizontal gene transfer) and from mother cell to daughter cells from generation to
generation (vertical gene transfer)

In eukaryotes, the chromosomes are arranged in pairs called homologues. Each homologous
pair are inherited from both parents, one each from the male gamete (spermatozoon of the
father) and the female gamete or ovum (egg of the mother). This explains why the offspring bear
the traits of both parents. For instance, in human with 46 chromosomes, 23 come from the
father and 23 from the mother.

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Chromosomes are located in the nucleus. Note one of the chromosome enlarged and a part of the
DNA stretched out.
In the eukaryotes, the chromosomes are located in the nucleus so the nucleus controls all the
activities of the cell. Each unit of the DNA that determines a trait is called a gene which is a
stretch or sequence of the DNA molecule that synthesize specific protein that is responsible for
the expression of specific traits in any living thing. (See the plate above)

EVOLUTION
There is nothing in nature that is static but everything, living and living keep changing from one
form to another. The gradual change of living things from one form to another in order to adapt
to environmental changes over the ages is known as organic evolution or simply evolution. In
other words, living things come to their present form and function through a continuous process
called evolution. This gradual process involved modifications and changes brought about by
interactions with other organisms and the environment. As the conditions on the Earth changes
over the ages, the various organisms continue to develop structures that help them to survive
such that only the organisms that develop features that help them to adapt to the changes and
can compete with other organisms survive. Those that could not simply go into extinction while
others survive. This is known as the survival of the fittest.
As learnt earlier, there exist variation among living things belonging to the same species This
helps individual among the same species to be adapted to various situations to varied degrees.
For example assuming there is an outbreak of a disease in a biological community that affected
all members some may simply die because they lack resistance, some may have to struggle with
the disease for some time and develop behavioral adaptation to survive while few may not even
feel the effect of the disease not because they were not infected but because they have natural
immunity to it while the former may have developed acquired immunity and thus survive. These
three situations, illustrate that the best survive without stress because they already had features
that grant resistance, one developed the adaptive feature in the process while others simply
perish because they had no adaptive feature and could not develop any. This illustrate the
situation known as natural selection in which case the best is selected to survive and can
continue to carry on such resistance traits generation after generation.
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The modern synthetic theory of evolution has attributed the it two interrelated processes
namely – isolation and hybridization.
Isolation: This refers to the separation of population from one another. isolation can be
geographical in which case population is separated by geographical barriers such as high
mountains or large body of water or reproductive in which members of the population can no
longer interbreed for a very long period of time. Both situations result in genetic changes that
cannot allow them to interbreed successfully thus separating the population into distinct species
Hybridization: Sexual reproduction of distantly related members of the same species is known
to create new genetic recombination with better adaptive features to survive as well as thrive
better with even better reproductive ability. Unlike the old idea of survival of the fittest, it is
observed today that both strong and weak organisms exist together without anyone trying to
eliminate the other through a struggle for existence. Thus hybridization creates new species
rather than eliminating them allowing for more diversity of living things.

IN LIVING THINGS
Plants ADAPTATION

CHARACTER ADAPTATION EXAMPLE

Water and nutrient 1. Development of rhizoids in 1. Bryophyta, Hepatophyta

uptake primitive plants that live in
moist areas
2. Higher plants – Gymnosperms
2. Roots to tap water and nutrients e.g. Cycadophyta, Coniferophyta
in drier area

Transport nutrients Vascular tissues All higher plants

to other parts

Transpiration Stomata, lenticels Higher plants

Structural support Wood (lignin) Higher plants

Reproductive 1. Cones in gymnosperm 1. Cycadophyta, Coniferophyta,

adaptation Gnetophyta and Gingkophyta

2. Flowers in angiosperms 2. All flowering plants

(flowering plants)

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Desert (draught) Waxy cuticle to reduce Desert plants e.g. Acacia,
evapotranspiration

Fleshy stem and roots to for water

storage

Reduced leaf size into needle-like

structure.

Water plants Pneumatophores for gaseous exchange, Mangrove plants

aerial roots etc.

Animals:

CHARACTER ADAPTATION EXAMPLE

Aquatic Animals Flexible body, streamline body for easy movement Fishes, aquatic birds,
through water, gills for gaseous exchange, large sea lions etc.
body cavity for buoyancy, slippery body to escape
from predators, flat (webbed) paddle-like feet for
movement in water

Desert animals Thick skin to resist cold nights, ability to run fast,
nocturnal lifestyle to avoid the extreme
temperature of the day, far-sightedness,
possession of water storage pouch as in Camel,

Flight (Volant) Feathered wings in birds, light bones to float

adaptation. easily in the air, streamline body for easy gliding
through the air, farsightedness to be able to find
prey from afar, membranous wings in flying
mammals such as bats and flying squirrels

Escape from Camouflage, ability to move fast, spiny body,

predators. possession of poison fang and spray as in some
(Defence) cobra, nocturnal behaviour with ability to see in
low light

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Assignment:
Draw a chromosome showing the following parts – short arm (p), long arm (q), centromere (the
primary constriction), satellite, chromatid, secondary constriction.

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