BIOLOGY
THEME 1: ORGANISATION OF LIFE
TOPIC: RECOGNISING LIVING THINGS
Biology is the study of living things a branch of natural science, derived from two Greek
words: `bios’ meaning life and `logos’ meaning to study/knowledge. It is a science of life
that deals with all forms of life including their classification, physiology, chemistry, and
interactions. Biology is basically grouped into two main branches, Botany- the study of
plants and zoology the study of animals.
However, in modern times other major divisions include microbiology, bacteriology and
virology.It is important to note that biology is not partitioned so neatly as chemistry and other
disciplines have become interwined in it.leading to such fields as biochemistry,
ecology,physiology,and molecular biology.More so the study of biology involves its
application to areas as food science,nutrition,environmental science,industrial
microbiology,agriculture,animal science and behavioural biology.
Importance of biology and career choice
Man depends on plants and animals as sources of food, for transport and leisure.For these
reasons the knowledge of biology is necessary for him to be able to maximise the
management of his environment.Biology is important in agriculture,medical and veterinary
science, and biotechnology which involves the production of food,medicinal and industrial
materials using micro-organisms.
Careers in which biology is an essential component include Medicine,Dentistry,Pharmacy,
Nursing, Food Technology,Agriculture,Enviromental Science, Genetic Engineering,Forestry
Fishery Science and many others.
If we look around we can see a number of things which can be grouped into two: living and
non living things. Living things vary in size, shape, structure and ways of life. They differ
from non- living things by their ability to carry out the following functions which are known
as life processes. These processes are referred to as characteristics of living things.
Characteristics of living things living things exhibit physiological, structural, genetic,
evolutionary and ecological characteristics.
A) Physiological or functional characteristics
Movement: Movement means change in position which could be total as in animals, or
limited, as in plants. Animals generally move their whole bodies, from place to place in
search of food, shelter, mates or even as a means of escape and in most cases, with special
structures like pseudopodia, flagella, cilia, legs, wings, fins, movement in animals may also
involve certain body parts e.g churning of bowels ,knee jerks.Part movement of the body is
also seen in sedentary animals e.g. hydra. In most plants, movement is restricted to certain
part of the plant e.g. the opening and closing of petals or growth movements of shoot and
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roots.Such movements are slow and often in response to certain stimuli such as light, water
gravity or even chemicals.
Respiration: Both plants and animals respire both day and night taking in oxygen and giving
out carbon(iv) dioxide and water vapour.It is the breakdown of food substances taken in by
the organism to release energy. There are two types of respiration
a)Aerobic respiration, in which oxygen is needed to release energy; the energy released
enables the organism to carry out its life processes and maintain its complex body
organization.In some organisms,particularly the simple forms,oxygen simply diffuses through
their body surfaces.The higher organisms on the other hand have specialised structures that
handle oxygen that enters the body,the carbon (1v) oxide and water vapour that arise from
tissue respiration.
C6 H12O6 + 6O2_______________________ 6 CO2+ 6H2O +E
The reactants are: Carbohydrate food and Oxygen, While the products are carbon (iv) oxide
water and energy.Many organisms have special body parts for taking oxygen for respiration.
Example human beings use their lungs; fishes use their gills, while plants use openings in
their leaves (stomata) or stem (lenticels).
b)Anaerobic respiration, in which energy is released without the use of oxygen.
Nutrition: All living organisms feed for the purpose of generating energy to carry out all
biological activities for the replacement of worn-out body tissues (repair-services) and for
growth. Green plants contain pigments like chlorophyll which traps light energy,absorb
water,while carbon (iv) diffuses in through stomata and carry out photosynthesis (6CO2
+6H2O______________C6 H12 O6 +6O2. They are referred to as autotroughs other
autotroughs are algae and some bacteria.
Animals and fungi use chemical energy obtained from other living organisms (plant and
animals) on which they feed. Generally animals take in complex food substances, often in
solid form, which are later broken in to simpler forms during the process of digestion.
Irritability (sensitivity): This is the ability of an organism to respond to changes in both
internal and external environment (stimuli) to maximize its choice of survival. The changes
/stimuli include touch,pain,light,heat,chemical,cold,smel and sound.In simple microscopic
organisms like amoeba, sensitivity is simple while in higher animals like man, highly
coordinated sense organs and nervous systems have evolved and can respond to light, smell,
taste, temperature, etc. plants, on the other hand have no sense organs but respond in various
ways to light, gravity, heat or chemicals. Responses in animals are more precise, predictable
and rapid, while that of plants is rather slow,proloned and directional or non-directional.
Growth: Growth is an irreversible and permanent increase in size ,volume and weight or
complexity which usually accompanied by cell division and differentiation ,food eaten,help
repairs of worn-out body tissues. With good feeding, living organism increases it body mass.
When plants grow in girth,the form of growth is described as secondary growth. Apart from
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growth being a measure of physiological activity of the organism, growth rings have been
used to determine the age of certain organisms e.g. snails, fishes and plants.
Excretion: This is the removal of waste products of metabolism. Metabolism is the sum total
of the chemical processes which takes place within the cell of the body. From the continuous
activities of building up and breaking down processes that occur within the bodies of living
things, waste products are formed.This can be in form of liquid, semi-liquids or gases which
is often toxic and must therefore be removed. The process of such removal is known as
excretion. The excretory products are carbon (iv) oxide, water vapour, ammonia, urea and
sweat, while excretory surfaces include the lungs,skin,liver, gills, leaf surface etc
Reproduction: This is the process by which adult organisms give rise to new individuals of
the same kind,for example rice grain germinate in to rice seedlings It ensures the continuation
of the species. It could be sexual or asexual.
There are two types of reproduction: 1.Some times,reproduction will involve two different
parents. These parents produce specialised sex cells which fuse to form new individual This
is called sexual reproduction.
2.Asexual reproduction/vegetative reproduction:
Single parent may just divide several times to give rise to new individuals,without involng
any specialised sex cells
Adaptation: This is the way living organisms get used to their various environments in such
a manner that would be comfortable and be able to survive.
Competition:
Living things tend to struggle for many of the necessities of life in order to survive and be in
continuous existence in their various environments. They compete for light, space, water,
mates etc.
Aging and death: Aging is the physical and chemical changes that occur in living organisms
and are noticeable with time. these changes generally slow down the overall metabolism of
the organism concerned. For example, the active life of the organism is slowed down/
hampered, rate of food capture or even the utilisation of food will be slow, circulation will be
slow, growth ceases .
All living things must die because they have a definite and limited period of existence, be it
naturally, accidentally or due to infection. They must pass through these five stages of life
namely:
Birth----Growth----Maturity----Decline (old age) ----Death.
B) Structural characteristics: 1.Each living thing is made up of one or more cells.
2. .Each kind of living thing has a characteristic shape and size
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C) Genetic characteristics: 1. Every kind of living thing transmits the characteristics of the
species from the parents to the offspring through the genes.
2. Each kind of living thing has a constant number of chromosomes in each body cell.
D) Evolutionary characteristics: Each kind of living thing has evolutionary relationship
with other living things.
E) Ecological characteristics: Each kind of living thing is adapted to natural environment.
Non-living things: An examination of non-living things shows that they do not exhibit the
characteristics listed and discussed above but may perform few of them.For example, viruses
tend to be the link between living and non-living things While they can reproduce,within a
suitable medium,they cannot carry out any function of life.
Differences between Living and Nonliving Things
s/n Living things
Non- living things
1
Food is required to sustain life
No food is required
2
Growth is by the addition of new
material from within as a result of good
feeding, cell division and development
Growth is by accretion i.e. addition of
new materials to their outside surface
3
Capable of reproduction
Incapable of reproduction
4
Respiration is necessary
Respiration is not necessary
5
Excretion is necessary
Excretion is not required
6
Sensitive to external condition
Usually un affected by external condition
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Existence is rhythmic or periodic i.e.
living things lives for some times and
then die
It is inert. Non- living things don’t die
Differences between Plants and Animals: All plants and animals are living things and they
share similar characteristics, however, there are marked differences between them. These are
shown in the table below:
s/n
Animals
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Heterotrophic/holozoic mode of
Autotrophic/holophytic mode of nutrition,
nutrition, since animals cell contains no plant cell utilises chlorophyll ,carbon (iv) oxide
chlorophyll, they depend directly or
,water,dissolved minerals,solar energy to
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Plants
indirectly on plants
manufacture comlex food in the process of
photosyn thesis.
2
Animals move freely from place to
place, in search of food, shelter, or flee
from danger such as approaching
predators or un favorable conditions.
Most animals have special locomotory
organs with sense organs and nervous
systems to direct their
movement.pseudopodia in amoeba,cilia
in paramecium and tentacles in hydra
are some of the locomotory organs
Plants are generally static to a spot with
movements restricted to response to stimuli and
growth that is to say plants depend only on their
auxin /hormones to produce certain movements
which are often slow.Plant like organisms like
euglena and chlamydomonas which have
flagellum,show active movement in aqueous
environments.
3
Rapid response to external stimuli, have
well developed sense organs
Slow response to external stimuli, response may
take hours or even days no matter no sense
organs.
3
Rapid response to external stimuli,as
they havediffused or elaborate nervous
system with specialised organs or
organelles their reaction to stimuli is
there fore quick and sometimes
automatic
Slow response to external stimuli, response may
take hours or even days, no matter the intensity
of the stimulus, no nervous system, but depend
mostly on hormones for their reactivity.
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Growth is extended to all parts of the
body and is said to be
intercellulary,limited growth which
stops when they reach adult stage of
development
Growth only at the meristems (group of cells
capable of dividing). Growth in length occurs
only at the tips of stems and roots ( apical
growth )while growth in girth occurs at the
cambium. Unlimited growth- spreading body
form.
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No cell wall, it is bounded by cell
membrane the cytoplasm makes up
almost the entire cell. The vacuoles,
where present, are temporary and small.
Plant cells are surrounded by substance the
cellulose which forms the cell wall. Have a thin
lining of cytoplasm with a large central
permanent vacuole containing cell sap.
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Most animals use special organs for
exchange of gases between their
environment and their bodies. Such
organs include gills (aquatic animals)
and lungs (terrestrial animals)
Do not have special organs for respiration
excretion and coordination.Take in
carbon(iv)oxide in the day time and give out
oxygen to complement the process of photosyn
thesis
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Has no cell vacuole, with cell sap. It
may have food vacuole has plentiful
cytoplasm, which fills the cell.
A mature plant cell usually has some cell
vacuoles with cell sap. Has moderate amount of
cytoplasm which does not fill the cell
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In animals waste products include
water,carbob(iv)oxide and
ammonia,These are removed from the
body through special excretory organs.
The main waste products in plants are
water,carbon(iv)oxide and oxygen ( arising from
photosynthesis);usually, these products (except
oxygen) are stored away in certain cells until the
plant dies,
Organization of life: Living things are highly organised. The bodies of living organisms are
made up of small fundamental building units known as cells. Cells are living and are
generally grouped together for efficient functioning. This organization occurs in levels. The
simplest structures are found at the lowest levels and they interact to build up more complex
structures at the next level and so on. There are four levels of organization of life in
organisms. These are the cells, tissue, organs and system. The cell is the simplest of all these
levels.
Cells (first level): The cell is defined as the structural and functional unit of life. Some of
these living organisms are made up of only one cell hence they are called unicellular
organisms. Others are made up of many cells and are called multicellular organisms.
Unicellular organisms have a specific organelles that performs specific function e.g.
pseudopodia, cilia, flagella for movement. Examples of unicellular organisms at cellular level
of organisation are amoeba, paramecium, chlamydomonas, etc. These organisms are capable
of carrying out all the life processes such as movement, respiration, reproduction, etc.
examples of cells in higher plants are phloem cells, xylem vessels, etc. while example of cells
in higher animals include rod and cone cells in the eyes, ova or eggs, spermatozoa, nerve
cells, red blood cells, white blood cells, epidermal cells, etc.
Tissues (second level): A tissue is a group of similar cells forming a layer in an organism
which performs a particular function. In other words, a tissue consist of two or more different
types of cells aggregating together to perform a specific function. Examples of tissues in
higher plants are mesophyll layer in leaves, epidermal tissues, sclerenchyma tissue, xylem
tissue, parenchyma tissue in stem, phloem, etc. examples of tissues in higher animals include
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muscle tissue for movement,skeletal tissue for support and nervous tissue for perception of
stimuli and conduction of nervous impulses. Examples of organisms which exist at the tissue
level of organization of life are hydra, sponges ,fungi,jelly fish,sea anemones and coral
Just as cells specialize to perform different functions, tissues are organized in such a way as
to perform specific functions too e.g. muscle tissue consist of cells adapted in a way for
contraction and to cause movement. Nervous tissues are adopted for transmission of nerve
impulses, conducting tissues made of phloem and companion cells are specialized for
conducting food substances in the plant.
Organ (third level): An organ is a group of similar tissues forming a layer in an organism
which performs a specific function. Examples of organs in plant are flowers, roots, stems, an
onion bulb, a rhizome, a corm and a tuber. In animals example of organs include the heart
specialized for pumping blood round the body, kidneys used for excretion, lungs for
breathing, brain which co-ordinates nervous activities other organs are the skin, ears,
stomach, liver, etc.
System (fourth level): A system is a group of similar organs which work together to perform
a specific function. Examples of system in plant are the shoot system and the root system.
Examples of system in animals are digestive, reproductive, respiratory, excretory, skeletal,
nervous and circulatory.
All cells, tissues, organs and systems within an organism do not function independently of
each other but all co-ordinates in maintaining the life of the organism. Although everything
is centered on division of labour, they function harmoniously for the benefit of the organism.
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COMPLEXITY OF ORGANISATION IN HIGHER ORGANISMS:
There is an increase in complexity from unicellular organisms to multicellular organisms.
Even though unicellular organisms can perform all life processes, they still lack vital
tissues, organs or systems that is efficient and capable of ensuring their survival. As a
result of this, higher organisms have advantages and some disadvantages in complexity
over the unicellular organisms.
ADVANTAGES:
1. There is structural specialization of tissues,organs or system
2. Division of labour gives room for efficient exploitation of environment.
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3. This in turn brings about efficiency of tissues,organs or systems . 4.Increases
adaptation to environment-it becomes more resistant to adverse environmental
conditions.
5.One body function does not adversely affect other body functions as various systems
operate side by side without adversely affecting the other.
6.Reproduction in complex organisms does not lead to the breaking down of the parent’s
body, since that is a specialised system.But in a simple unicellular organisms,parents
disintegrate after reproduction or conjugation.
DISADVANTAGES:
1. Due to diminished surface area relative to volume, more effort is required for
diffusion over the general body surface.
2. The distance covered before oxygen and food materials obtained by the constituent
cells pose a lot of difficulties.
3. More effort is needed to eliminate toxic waste.
4. Energy and time are wasted.
5. Rate of diffusion decreases.
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Classification of Living Things
Biologist have examined and described millions of living organisms but there are
many more to be discovered. It would be very difficult to study them without orderly
arrangement. Therefore similar plants and similar animals with certain features in
common are grouped together.The grouping of living things into their kinds is called
classification. Classification can be described as sorting, ordering and grouping things
into sets. .The main reason for classification is for the convenience of the user. Think
of the motor pack, the books in the library, and the goods in the shop or market it
makes it easier to the user so also that of living things is made easier to study them.
The science of classification is referred to as taxonomy. Taxonomy deals with
identification and naming of organisms. Identification and placing organisms into
groups on the basis of their similarities and differences is referred to as systematic,
Aristotle (384-322 BC) a Greek philosopher was the first to make an attempt to
classifying living organisms.
A lot of considerations were made on the classification of living organisms but there
were lapses. In the present day classification of plant and animals, all the
characteristics of plant and animals are used. This reflects the natural and
evolutionary relationships that exist among the living things- practically, organisms
which have the largest number of characters in common are considered to be must
closely related by evolutionary descent.
Living things are first split into kingdom like plant and animal kingdoms. The
kingdoms are further split into a large number of smaller groups called phyla (singular
phylum) for animals and division for plants. All members of a phylum or division
have certain features in common. Each phylum or division is broken down into
classes then into orders, orders into families, families into genera (singular genus),
generate into species. The arrangement of living things in this hierarchy from the
highest to the lowest level is shown below:
Kingdom
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Phylum
Division
Class
Order
Family
Genus
Species
The basic unit of classification of living things is the species. Species is the smallest
unit containing members which have the largest number of features in common and
usually interbreed with a member of another species. For example, all human beings
belong to one species and all monkeys belong to a different species. So both human
beings and monkeys cannot interbreed.
Modern classification recognizes five kingdoms namely:
1. Monera, 2. Protista/protoctista 3. Fungi 4.Plantae 5. Animalia
Kingdom Monera:
1.
2.
3.
4.
5.
They are unicellular, microscopic
The cell is prokaryotic i.e lacks a true nucleus and a nuclear envelope
The cell contains one strand of DNA ,not bound by nuclear envelope
Organelles such as mitochondria are absent.
The cell has a complex, rigid cell wall which lacks cellulose but consists of
polysaccharides and amino acids.
6. Reproduction is by binary fission
7. Some are autotrophic, and some are heterotrophic.Example Bacteria and blue-green algae
Kingdom Protista:
1. They are eukaryotes,
2. Possess distinct nucleus and organelles,
3. The are microscopic, single-celled,
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4. They may be aggregate (form colonies)
5. The different classes are characterized by their locomotory organelles.
Examples are protozoa (e.g. Amoeba, Paramecium, Trypanosome, diatoms, and Euglena
e.t.c.)
Kingdom Fungi:
1.
2.
3.
4.
5.
6.
7.
8.
They are plant-like
They don’t have chlorophyll
No true leaves, stem and roots
Most fungi are saprophytes i.e. decomposers which make use of food present in dead
plants and animals. They break down food into simple absorbable product.
They reproduce rapidly by producing spores (asexual reproduction) although others like
rhizopus reproduces sexually.
Some fungi are parasites.
Most fungi consist of branching thread-like structure called hyphae (singular). These form
several braches in the dead plant or animal. The branches form a network known as the
mycelium.
A hypha has a wall made up of a nitrogenous material known as chitin.
Examples are club fungi (e.g. mushrooms, bracket fungi and puffballs, sac fungi (e.g.
mould) bread moulds and slime moulds.
The Plant Kingdom: Thallophyta
1. They are eukaryotes.
2. They are multicellular.
3. Possess chlorophyll.
4. Possess cell walls.
5. Examples are red, brown & green algae in addition to more complex groupsbryophyta and tracheophyta.
Algae: (Thallophyta)
1.
2.
3.
4.
5.
Include red, green and brown algae
They are mostly sea weed
They reproduce asexually by cell i.e. fragmentation or spores
They also reproduce sexually by conjugation
Simple plant with no true roots, stems, or leaves. They possess thread like
(filamentous) or flat (thalus) bodies e.g. spirogyra, red and brown algae.
Bryophyta:
1.
2.
3.
4.
They do not possess roots, stem and leaves.
They are non-vascular in nature.
They reproduce using water.
They grow in damp/wet places or land.
Examples are mosses and liverworts.
Tracheophyta:
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1. They are vascularised (i.e. conduct water, mineral salt dissolved food.
2. They possess true leaves, stems and roots. examples are ferns and horsetails, seed plantsgymnosperms (conifers and angiosperm), flowering plants like monocotyledons and
dicotyledons
Animal Kingdom:
1.
2.
3.
4.
5.
6.
7.
They are multicellular organisms.
They are eukaryotes.
They cannot contain cell walls.
They possess cell membranes.
Chlorophyll is absent.
They cannot manufacture their own food.
They take in food through digestive process. Examples are invertebrates and
vertebrates (phyla).
Invertebrates: they do not have backbones e.g. coelentrata:
1.
2.
3.
4.
5.
6.
They are multicellular aquatic animals.
Possess cylindrical and radially symmetrical bodies.
They are two-layer thick.
They only contain one opening-the mouth (i.e. no anus)
They possess tentacle which are used in picking food.
The tentacles also contain stinging cells with which they paralyses their preys.
Examples are hydra, sea anemone, jelly fish and corals.
Flatworm (platyhelminthes):
1.
2.
3.
4.
5.
6.
They are small, flat and without body cavity or lumen.
Possess only one opening into alimentary canal.
They are bilaterally symmetrical.
They have three later.
They possess excretory, reproductive and nervous systems
They are mostly hermaphrodites (with both male and females reproductive organs in
one)
7. They may be free-living or parasitic. Examples are tapeworm, planaria, fasciola (liver
flukes) and bloody fluke (schistosoma).
Roundworms (Nematoda)
1.
2.
3.
4.
5.
6.
7.
They have elongated bodies that are pointed at both ends
They are cylindrical in nature
They are three layer thick
They are no body cavities
Their bodies are similar
Their digestive system is made up of mouth and anus
They possess well developed excretory, digestive, reproductive and circulatory
systems.
Examples: hook worm, thread worm, guinea worm and filarial worm.
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Annelids (Annelida):
1.
2.
3.
4.
5.
6.
7.
8.
They are segmented worms
Their segments are of similar compartments
They possess cylindrical and elongated bodies
Their bodies are three layers thick
their digestive system have two openings-mouth and anus
They possess closed circulatory system
Their reproductive, excretory and nervous systems are well developed
Most of them are aquatic e.g. leeches. example is earthworm.
mollusca:
1.
2.
3.
4.
5.
6.
7.
8.
Their bodies are soft and non-segmented
Their bodies are three-layered
Some have their bodies covered with calcerous shell
Their stout bodies have head and muscular feet
Their eyes and tentacles are used for sensitivity
Their body is covered by a soft tissue called the mantle
They respire by gills or a lungs in the mantle cavity
The shells are secreted by the mantle
Examples are snail, scallop (with shells), slug and octopus (without shells).
Arthropoda:
1.
2.
3.
4.
5.
They have segmented bodies
They are covered with exoskeleton of chitin
Their bodies are made of three layers (head, thorax, abdomen)
They have jointed appendages
They are the largest of the all phyla.
Examples are of five division or classes, namely crustaceans (crayfish and crabs),
arachnids (spiders), chilopods (centipedes), diplopods (millipedes) and insect (flies,
cockroaches and beetles).
Table showing differences among insects, crustaceans and arachnids
Class
Walking
legs
Antennae
Respiratory
organ
Eye
Division of
the body
insect e.g.
house fly
3 pairs of
jointed legs
a pair
trachea with
spiracle
a pair of
compound
3-head,
thorax and
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crustaceans
e.g. crab
5 pair of
jointed legs
arachnids e.g. 4-pairs of
spider
jointed legs
eye
abdomen
2 pairs
Gills
a pair of
stalked eyes
2cephalothorax
and abdomen
Non
lung books
eight simple
eyes
2-prosoma
and
opisthosoma
Echinoderms (Echinodermata):
1.
2.
3.
4.
5.
They are radially symmetrical
Their body plans are based on five (five rayed symmetry)
They are triploblastic coelomates (3 layered body)
Their larvae are segmented while adults are unsegmented
Adults’ coloem is made up of perivisceral cavity and water vascular system this
dilates the numerous tube feet.
6. There is exoskeleton of the dermal calcerous ossicle
7. No specialized excretory organs
8. Have spiny skin
9. No head nor brain and the body is segmented
10. Tube feet for locomotion
Examples are sea urchins, starfish and sea cucumbers.
vertebrates:
Are known to possess backbones or prebackbones-notochords (acorn worms and
tunicates).
They are divided into five classes, namely: Pisces, amphibians, reptiles, birds and
mammals (mammalia).
Characteristics of Vertebrates:
1. Presence of jointed endoskeleton that are either bones or cartilage
2. They are bilaterally symmetrical.
3. At one stage or the other possess gill slits.
4. They have their skin covered with scale, hairs or feathers.
5. They have single hollow nerve cord.
6. Body divided into head, trunk and tail.
7. Two of limb- pectoral and pelvic.
8. Well developed and controlled nervous system with brain and spinal cord.
9. Triploblastic
10. There is a closed blood system.
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Fishes:
1. They dwell in water.
2. Their bodies are streamlining.
3. Their skin are covered with slimy scales
4. They respire with the aid of gills.
5. Movement is made possible by fins.
6. The presence of lateral lines helps to detect vibrations.
7. They possess homodont dentition
8. They are poikilothermic (clod blooded)
9. They reproduce by laying eggs (oviparous)
10. Two chambered heart
11. Reproduce sexually with external fertilization
12. Possess swim bladder for buoyancy in water.
Examples are cartilaginous fish (dog fish, shark, and Rays) and bony fish (tilapia, eel and
cat fish).
Differences between bony fishes and cartilaginous fishes
Cartilaginous fish
Bony fish
1. Operculum is not present
operculum is present
2. Scales are placoid
scales are cycloid
3. Mouth is ventral
mouth is apical
4. Have 5-7 pairs of gills
have
5. Gills are of separate clefts
Gills are on common cleft
6. Skeleton is cartilaginous
Skeleton is bony
7. Tail is heterocercal
Tail is homocercal
8. Swim bladder is absent
Swim bladder is often present
9. males possess claspers
Claspers absent in males
AMPHIBIANS:
1.
2.
3.
4.
5.
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They live partly in water and partly in land.
They don’t have scales.
Their skins are always moist.
They respire with gills at larval stage and skin and mouth at adult stage.
Some have poison glands in their skins of defense.
6. They are poikilothermic (cold blooded).
7. They are oviparous (they exhibit external fertilization).
8. The young once i.e. tadpoles are herbivorous while adults are carnivorous in feeding.
9. Have chambered heart.
10. Have sticky tongue which can be protruded or retracted quickly.
Examples are toads, frogs, salamander and newts.
REPTILES:
1. Most of them live in land (terrestrial) while a few live in water (aquatic).
2. They are cold-blooded (poikilothermic).
3. Their skins are covered with scales.
4. They have homodont dentition (tooth of same shape).
5. They have jaws with teeth set in socket.
6. Apart from the snakes, they have two pairs of legs.
7. They oviparous (lay eggs).
8. Have longs for respiration.
9. Reproduction is sexual with internal fertilization.
10. sThey show parental care.
11. They possess incomplete developed four chambered heart.
Examples are lizard, crocodile, tortoise, snake and turtle.
BIRDS (AVES):
1. They warm blooded (homoeothermic).
2. They live on land (terrestrial) while some of them live on tree (arboreal).
3. They possess feathers for flight, even though, in some like domestic birds, penguine
and ostrich, little use in made of them.
4. They naturally light (especially those that fly).
5. They possess hollow bones.
6. They have scaly legs and beaks.
17
7. Some are carnivorous (e.g. heron eat fish and woodpeckers eats insect while some are
omnivorous e.g. domestic fowls.
8. They lay eggs (oviparous) with internal fertilization.
9. They feed on concentrated foods like grains which supply them the needed energy to
fly.
10. Their streamlined body reduces the effect of the opposing air during flight.
11. They good eyesight.
12. They have only inner and middle ears.
13. They have four chambered heart.
14. They are toothless.
MAMMALS (MAMMALIA):
1. Possess mammary gland called mammae.
2. They breast- feed their young once with milk.
3. Their bodies are covered with hairs or furs.
4. They chest ca by the cavity is demarcated from abdominal cavity by the diaphragm.
5. The organ lies outside their body.
6. They possess external ears called pinnae (singular pinna).
They have heterodont dentition (different kind of teeth).
7. They viviparous (deliver their young ones alive); even though few, like duck- billed
platypus and echidna lay eggs.
8. The marsupials deliver their young ones at very early stage of development, only to
mature outside their parents’ body (in the pouch-kangaroo and opossum). This is
ovoviviparous reproduction.
9. They are warm-blooded (homoiotherms).
10. Their skin contains sweat gland e.g. sebaceous gland.
18
11. Bilaterally symmetrical.
12. Have lungs for respiration.
SUMMARY OF CLASSIFICATION
Living things
Prokaryotes
eukaryotes
1. Bacteria e.g. staphylococcus spp
2. Virus e.g. rhino virus
3. Blue-green algae e.g. nostoc
Protista
Fungus
1. Protozoa
Anima kingdom
1. Club fungi
e.g. amoeba
e.g. mushroom
2. sac fungi
e.g. mould
Plant kingdom
1. Algae e.g spirogyra
2. Bryophyte e.g
mosses and liverwort
3. Tracheophyta e.g
3. bread mould
ferns, horsetail,
4. slime mould
Gymnosperm and flowering plant
19
Vertebrates
1. Pisces (fishes)e.g tilapia
2. Amphibian e.g frog and salamanda
3. Reptile (reptiles)e.g lizard, crocodiles
invertebrates
1. Coelenterates e.g hydra
2. Plathyhelminthes e.g
flatworms
4. Aves(birds) e.g vulture, pigeon
3. Roundworms(nematode)
5. Mammalia e.g man, goat, elephant etc
4. Annelida e.g earthworm
5. mollusca e.g snail and Scallop
6. Athropods e.g
crustaceans,
Arachnids, chilopods,
Diplopods & Insecta.
7. Echinoderms e.g
Starfish and sae urchins
20
EXAMPLE;Classification of domestic dog, man and lion
Dog
Man
Lion
Kingdom:
Animalia
Animalia
Animalia
Phylum:
chordata
chordate
Chordata
Class:
Mammalia
mammalia
mammalia
Order:
Carnivora
primate
Carnivora
Family:
Canidae
Hominidae
Felidae
Genus:
Canis
Homo
Panthera
Species:
Familiaris
sapiens
leo
The scientific name of domestic dog is canis familiaris ,for man is Homo sapiens and for lion
is Panthera leo
Assignment
Classification of rice:
Kingdom
plantae
Division(Phylum)
Tracheophyta
Class
Angiospermae
Order
Graminales
Family
Graminacea
Genus
Oryza
21
Species
sativa
Binomial System of Nomenclature
Carolous Linnanaeus also introduced a system of naming living things which is popularly
used by biologist today. The system is called binomial system of nomenclature, that is each
organisms is given two names, hence the name binomial nomenclature. The first name is the
generic names (common to the genus), which always begins with capital letters. The second
name is the specific name and it begins with a small letter. These scientific names are written
in italics or underlined.
The old and most widely used classification adapted from Linnaeus was based on only two
kingdoms ---animals and plants. This classification worked with familiar organisms, e.g.
grasses, mango tree, and baobab are plants, dogs, cows, and lions are animals. However,
certain organisms like sponges and bacteria cannot fit in so easily into either of the two
kingdoms, hence the need for other kingdoms based on better understanding of the cellular
structures of the organisms. Modern classification recognizes five kingdoms. They are
monera, protoctista (protista), fungi, plantae and animalia.
Kingdom monera
(i)bacteria (ii)cynobacteria
Kingdom protoctista
(i)protozoa(ii)fungus like protista and slime
moulds(iii)plant like protoctista(a)euglena
(b)crysophyta (c) pyrryhophyta
Kingdom fungi
(i) bread mould (ii) mushrooms and toad
stools (iii) yeasts
KINGDOM PLANTAE
(i) thylophyta (algae) (ii) embryohpyta (a)
bryophyte (b) tracheophyta (vascular
22
plants) 1.pteridohpyta (ferns) 2.
spermatophyte (seed plants) (i)
gymnosperms (ii) angiospermsdicotyledon-monocotyledon.
KINGDOM PLANTAE
(i) thylophyta (algae) (ii) embryohpyta (a)
bryophyte (b) tracheophyta (vascular
plants) 1.pteridohpyta (ferns) 2.
spermatophyte (seed plants) (i)
gymnosperms (ii) angiospermsdicotyledon-monocotyledon.
Kingdom Animalia
(i) invertebrates (a) sponges (b)
Colenterates (c) Platyhelminthes (Flat
Worms) (d) Nematodes (Round Worms)
(e) Annelids (f) Mollusks (g) Arthropods
(h) Echinoderms (i) (ii) Vertebrata
Pisces
Amphibians
Reptiles
Aves
The Cell as a Living Unit
23
Mammals
The cell is defined as the structural and fundamental unit of a living organism (the simplest,
smallest unit of life). All living things are made up of cells.
Forms in which living cells exist:
1. As independent or single and free living unit as in Amoeba, Paramecium, Euglena and
Chlamydomonas. Each organism,even though it has only one cell,can carry out all the life
processes such as feeding, movement ,reproduction sensitivity excretion,growth,etc
2. As a colony Some organisms are made of many Identical cells which are joined or
massed together but they cannot be differentiated from each other This aggregation of
independent cells or protists is called a colony as in volvox, Pandorina and Sponges. The
cells in a colony usually have cytoplasmic connection.
3. As a filament Certain cells are organized in to filaments in which identical cells are joined
end to end. to form unbranched filaments. Each cell functions as an independent living cell.
24
Such organisms are multicellular and therefore exist as filament as in
spirogyra,Zygnema,Oscillateria and Oedogonium.
4.
Cell as part of a living organism: In multicellular organism, cell of similar size,
structure and function are grouped together to form a tissue. Tissues that performing specific
functions are collected together to form organs while several related organs combined to form
systems. An individual cell in a tissue or organ or system cannot independently function on
its own. The cells depend on one another for the proper functioning of the organism.
25
Different Types of cells
History of the Cell and Cell Theory
Many scientists contributed to the history of the cell. Among them are:
26
1) Robert Hook, an English scientist was the first to discover the hony comb structure of the
cell in 1665. In his book, Micrographia, he described his observations of a magnified thin
slice of a cork of an oak tree, as made up of thin components or rooms. He then named the
components. Cell
2. Felix Dujardin, a French biologist in 1835 discovered that the cell was made up living
substance. He however named the living substance Protoplasm.
3. Mathias Schleiden, a German botanist in 1838 revealed that the bodies of plants are made
of cells which were described as units of life.
4. Theodor Schwann, another German zoologist in 1839 also discovered that the bodies of
all animals are composed of cells.The discoveries of Schleiden and Schwan led to the
postulation of the cell theory in 1839.
5. Rudolf Von Virchow,a German biologist in 1855 concluded in his research that all cells
come from previously existing cells.
Cell theory was then proposed as a result of their discoveries on plant and animal cells, the
theory states that the cell;
27
i)
Is the structural and functional unit of all living things;
ii)
All living organisms are made up of cells
iii)
All living organisms originate from pre-existing cells.
iv)
There is no life apart from the life of cells.
v)
All living things are either single cells or group of cells.
vi)
All cells contains hereditary materials
Cell Structure
There are two types of cells. Plant and animal cells. They are as shown below:
Diagramme of Typical Animal and plant cells
Plant and animal cells have the same basic structure but differ in size, forms and
functions, degrees of specialization and mean generation time. They have structures
which are common such as cell membrane, cytoplasm and nucleus.
28
Differences between plant and animal cells
Plant Cell
Animal Cell
There is cellulose cell wall
No cellulose cell wall
Definite shape
No definite shape
There is chlorophyll
Chlorophyll is absent
Large and conspicuous vacuoles
Small and many vacuoles
Larger than animal cell
Smaller than plant cell
In mature cells, the cytoplasm is restricted
Cytoplasm fill up the entire space enclosed
to cell wall lining
within cell membrane.
Nucleus is pushed to the side of the cell
Nucleus is centrally located
Functions of Cell Components
Structure
Description
Function
Cell wall
Non-living usually made of
Provides rigidity to cell and
cellulose. Freely permeable to water
gives it a definite shape
and substances
Cell membrane
Living and differentially permeable
Allows selective movement
to water and substances
of materials into and out of
the cell
Cytoplasm
29
Semi-fluid mass enclosed within the
The largest and liquid part
cell membrane contains many
of the cell in which
organelles
metabolic reactions occur.
Nucleus
Enclosed by a nuclear membrane.
Store and carry hereditary
Contains chromatin and nucleolus
information from
generation to generation.
Translate genetic
information into the kind of
protein characteristic of a
cell. Controls the cell’s life
processes.
Vacuoles
Fluid filled spaces in the cytoplasm
Help in maintaining
turgidity in plant cells
Mitochondria
Double membrane system, found in
Major site for cellular
all cells. Contains the enzymes for
respiration to provide
cellulose respiration.
energy in cell metabolism,
and for all life processes
kreb’s cycle and electron
transfer system take place
in the mitochondria
Endoplasm
A complex folded double walled
Responsible for storing
membrane system
proteins exchange of
substances between the
nucleus and the cytoplasm
Ribosomes
Sac-like structure that contain
Responsible for storing,
enzymes
transporting proteins and
exchange of substances
between the nucleus and the
cytoplasm
Centrioles
Chloroplasts
30
Rod like structure always a right
Determine the plane of cell
angle to each other near the nucleus
division
Membrane bound organelles in plant
They are sites for
cells that contain light absorbing
photosynthesis
molecules of chlorophyll
Properties and Functions of a Living Cell
The living cell as the basic unit of life exhibits all the characteristics of living things
explained earlier on they are nutrition, respiration, excretion, growth, response to its
environment (irritability), movement and reproduction.
All these properties will be dealt with in greater detail.AFeeding is the process by which
organisms, typically animals, obtain food. Feeding are of different types such as (1)
filter feeding which is obtaining nutrients from particles suspended in water. Filter
feeders are aquatic animals and have to let water through sieve-like structures in their
body, in order to collect a reasonable quantity of their prey r; (2)Deposit feeding:
obtaining nutrients from particles suspended in soil;(3) Fluid feedingTwo types of
animals are grouped as fluid feeders. The first type consists of those that rest within,
or wallow in, their foods, e.g. the tapeworm in human intestine, which could,
therefore, be called a wollower. The second type is the suckers. They are mainly
insects which feed by sucking fluids from plants and animals. Examples are bugs, e.g.
aphids, butterflies and mosquitoes.This follows an evolutionary trend of some sort.
The complexity tends to increase from simple animal to complex ones like man.
Mineral Nutrition in plants
Plants require a number of in organic nutrients for healthy and normal growth. They
absorb these from the soil through their root hairs. Some of these nutrients are needed
by plants in large amounts. Such nutrients are known as macronutrients or macro
elements (essential elements). A few other nutrients are needed by plants in trace
amounts such nutrients are known as micronutrients or micro elements (non –
essential). The macronutrients are carbon, hydrogen, oxygen, nitrogen, potassium,
calcium, phosphorus, magnesium, iron and sulphur. They are also called major
elements.
31
The plant micro nutrients are chlorine, copper, manganese, zinc, molybdenum and
boron. They are also known as minor elements. Mineral elements are absorbed as
ions from the surrounding water in aquatic plants and from the soil in the case of
terrestrial plants.
The roles of plant nutrients.
There are many ways in which the macro nutrients and the micro nutrients are
involved in plant metabolism.
Element
Form in which nutrient is
absorbed
Function in plants
Deficiency symptoms.
Carbon
(CO2)
Major component of
organic molecules for
photosynthesis bulk
of plant .
Basic unit of life
Oxygen O
(O2, H2O)
Major component
Basic unit of life
Hydrogen H
CH2O
Major component of
organic molecules
photosynthesis
Basic unit of life
Nitrogen N
(NO-3, NH+4)
Component of amino
acids, proteins,
nucleic acids,
chlorophyll coenzymes.
Very little growth,
leaves become
chlorotic (turn
yellow), seedling is
weak.
Potassium K
(K+)
Component of
enzymes, proteins
synthesis, operation
of stomata cell
membrane formation.
Poor growth,
yellowing of leaves.
Calcium Ca
(Ca++)
Component of cell
walls, maintenance of
membrane structure
and permeability
activates some
enzymes.
Stunted growth, poor
root growth leaves
become deferred, stem
is short and week.
Magnesium
(Mg++)
Component of
chlorophyll,
Leaves turn yellow.
C
32
Mg
molecule, activates
many enzymes
Phosphorus p
(H2PO-4, HPO=4)
Component of ADP
and ATP, nucleic
acids, phospholipids,
several co-enzymes.
Little growth and poor
root development
Sulphur
(SO=4)
Components of some
amino acids and
proteins, co-enzyme
Poor growth, leaves
turn yellow.
Chlorine CL
(CL-)
Osmosis and ionic
balance
Curled and leaves with
patches of dead tissue
(necrotic leaves)
Iron
(Fe++ or (Fe+++)
Chlorophyll
synthesis,
cytochromes (iron
containing pigment)
Leaves turn yellow
stunted growth.
(Mn++)
Activator of some
enzymes.
Leaf malformation,
necrosis and chlorosis.
(Zn ++)
Activator of many
enzymes, chlorophyll
formation.
Poor leaf
development,
internodes fail to
elongate.
(BO-3 or B4O7=)
Healthy growth, and
cell division of
meristematic cells.
Growing tips
damaged, Tissues are
hard leaves are
distorted.
(Cu++)
Activator or
component of certain
enzymes.
Plants become rough,
reduced flowering.
(Mo O=4)
Nitrogen fixation,
nitrate reduction.
stunted growth,
necrosis chlorosis.
S
Fe
Manganese
Mn
Zinc
Zn
Boron
Bo
Copper
CA
Molybdenum
Mo
33
In order to investigate the roles or functions of the various, mineral elements in plant growth, it is
necessary to set – up an experiment, where a series of seedlings are grown in solutions, each
of which lacks just one of the essential elements necessary for plant growth. These plants are
compared with “control plant” grown in normal culture solution containing all the necessary
elements. These solutions are called water cultures. The experiment is called water culture
experiment. The experiment is also carried out to ascertain which elements are essentially
required by plants for their normal growth, and which are absorbed incidentally, and also to
find out the effect of lack of such essential elements on plant growth.
Absorption of Mineral elements
Plants absorb mineral elements from the soil solution by the roots and are then translocated to
various parts. The mineral elements are absorbed inform of ions. Their passage into the root
hairs is quite independent of the passage of water by osmosis. The component ions of the
elements are taken up individually and independently of one another. Mineral absorption
mechanism may be affected by various processes, constituting what is known as passive
absorption and active absorption.
RESPIRATION
Respiration is the breakdown of food substances to release energy.
Respiration takes place in the mitochondria of cells. The energy released in respiration is
stored as ATP (adenosine triphosphate). If oxygen is required in the braking down process,
the respiration is said to be aerobic. If the process takes place in the absence of oxygen, it is
called anaerobic respiration.
Aerobic Respiration
Aerobic respiration is the breaking down of food substances in the presence of oxygen to
release a large amount of energy. Water and carbon (iv) oxide are also produced.
C6H12O6 + 6O2 → 6H2O + 6CO2 + 2880KJ
Anaerobic Respiration
This is the breakdown of food substances in the absence of oxygen to release a little amount
of energy. Alcohol and carbon (IV) oxide are also produced.
34
C6H12O6 →2C2H5OH + 2CO2 + 210KJ
A form of anaerobic respiration is alcohol fermentation. Fermentation is the process of
breaking down glucose (sugar) into carbon (IV) oxide, and energy, by the enzymes in the
yeast, called zymase.
Energy Release in the Cell
Glycolysis: is the anaerobic (without oxygen) break down of glucose to pyruvic acid with
the release of a small amount of energy. Glycolysis takes place in the cytoplasm of the cell.
The amount of energy ordinarily released is 2ATP. 6ATP is got from the reduction of NAD.
NAD is produced in the conversion of glycerate to glyceric acid.
Kreb’s Cycle: is the complete breakdown of pyruvic acid to release energy. Kreb’s cycle
takes place in the mitochondria of cells. The amount of energy released in kreb’s cycle is
30ATP. A total yield of energy from a molecule of glucose is 38ATP.
In animals, such as man, excess pyretic acid is reduced to lactic acid CH3CH(OH).COOH, which is
returned to the liver for the synthesis of carbohydrates. This happens when the oxygen
concentration is low. In certain plants, anaerobic
respiration occurs. Yeast for example
convert the pyruvic acid to acetaldehyde and then to ethyl alcohol (ethanol)
Differences Between Aerobic and Anaerobic Respiration
Aerobic Respiration
(i)
(ii)
Oxygen is required for Oxygen is
oxidation.
oxidation.
By-products are water and
carbon dioxide.
not
required
for
By-products are alcohol or lactic
acid.
(iii)
More energy is released.
Less energy is released.
(iv)
It
takes
place
in
mitochondria.
water is given off as byproduct.
It takes place in cytoplastm.
(v)
35
Anaerobic Respiration
Alcohol is given off as byproduct.
Summary of Processes in Kreb’s Cycle
Kreb’s cycle takes place in the mitochondria and the processes are summarized as follows:
1. In the presence of oxygen, acetate which is derived from pyruvate as a result of
decarboxylation enters the kreb’s cycle as acetyl-coenzyme A (acetyl-co A).
2. The condensation of acetate with oxaloacetate results in the formation of citrate. The
citrate becomes isomerised into isocitrate.
3. Isocitrate is then decarxylated into a C5 compound called α-ketoglutarate.
4. a-ketoglutarate is further decarboxylated into C4 compound called succinate.
5. Succinate is dehydronated into funmarate. Fumarate pick up a molecule of water to
form malate.
6. Malate is dehydrogenated into oxaloacetate and the energy rich compound ATP is
formed.
A total of 30ATP molecules are produced by the complete oxidation of one molecule of 6carbon sugar in kreb’s cycle.
Summary of Kreb’s Cycle in the Presence of Oxygen
2C2H3OCOOH + 2H2 + 6CO2 → 6CO2 6H2O + Energy
Summary of Kreb’s Cycle in the Absence of Oxygen
In the absence of oxygen, the pyruvic acid is converted to ethanol in plants. In animals, in the
absence of oxygen, the pyruvic acid is converted to lactic acid.
The sum total of the chemical processes that occur in living organisms, resulting in growth,
production of energy, elimination of waste material, etc.
•
Anabolism- build up of complex molecules
•
Catabolism- break down of complex molecules
Usefulness of food: Food is eaten every day because it is required to :
Supply energy for various activities
Help organisms to achieve reproduction
36
Provide the necessary nutrients for growth
Repair worn out tissues
Fight against diseases keeping the body healthy
Provide heat to warm the body(via temperature control)
Aautotrophic nutrition is a type of nutrition in which organisms manufacture their food,they
are of two types photosynthesis and chemosynthesis while those that depend on readymade
food are said to be heterotrophic.
EXCRETION
Definition: Excretion is defined as the process by which organisms get rid of waste products during
its metabolism. The reason for excretion by all living things is to get rid of metabolic wastes which
are poisonous or toxic to the body system when they are not removed. Different organisms use
different means of removing waste products from their body systems.
The table below shows the excretory organs/organelles and waste products of some organisms.
Organisms
Excretory Organs
Waste Products
(i)
Protozoa, e.g Amoeba and
Paramecium
Body surface and contractile
vacuole
Carbon dioxide, water, excess
mineral salts.
(ii)
Flat worms, e.g. tapeworm
Flame cells
Water, urea, carbon dioxide and
nitrogenous waste.
(iii)
Round worms e.g.
earthworm
Nephridia
Carbon dioxide, urea,
nitrogenous waste.
(iv)
Insects e.g cockroach,
housefly
Malphighian tubules
Carbon dioxide, water and uric
acid
(v)
Vertebrate e.g mammals
Lungs, skin, liver, kidney
Water, carbon dioxide, mineral
salts, sweat, nitrogenous waste
(vi)
Flowering plants, e.g.
tannis,
Stomata, lenticels
Water, oxygen, carbon dioxide,
alkaloids, gums mucillage, lipids,
37
latex, resin and oils.
To be corrected
Structure
Function
Double membrane system, found in all
Major site for cellular
cells. Contains the enzymes for cellular
respiration to provide energy
respiration.
in cell metabolism, and for all
Organelles
Mitochondria
life processes kreb’s cycle and
electron transfer system take
place in the Mitochondria
Endoplasm
A complex folded double walled
Responsible for storing
membrane system
proteins and exchange of
substances between the
nucleus and the cytoplasm
Ribosomes
Sac-like structure that contain enzymes
Responsible for storing,
transporting proteins and
exchange of substances between
the nucleus and the cytoplasm
Centrioles
Chromoplasts
Rod like structure always at right angle to
Determine the plane of cell
each other near the nucleus
division
Membrane bound organelles in plant cells
They are sites for photosynthesis
that contain light absorbing molecules of
chlorophyll
Cell enlargement and differentiation
Cell division is usually followed by cell enlargement and cell differentiation. For instance, of the cells
formed by the cambium in a plant, some specialize into xylem, and some into phloem cells. Again,
all the cells in a human body come from one original cell, the zygote. However, as cell division
38
continues, some cells differentiate into nerve cells, others into bone cells others into skin cells,
muscle cells and so on.
Observing cell division
Material required
A variety of prepared slides of root tips, microscope.
Procedure
1.
Examine under the microscope, each of the slides provided.
2.
Make a high power magnification drawing of as many of the cells as you require to give you
a complete story of the process of cell division or mitosis.
Environmental Factors that affect growth
Several environmental factors affect growth. You may have observed that many plants grow
faster in the rainy season, when water is available in adequate amounts than in the dry season
e.g. mango plant. In the dry season, the shoots of some plants die, and the plants survive the
dry season by means of seeds (e.g. cowpea, maize) or underground parts e.g. yam, cocoyam.
Growth requires synthesis of new protoplasm and other body materials such as cellulose (in
plants). Food is necessary for synthesis of protoplasm and body materials. Energy obtained
through respiration is also necessary for synthesis of body materials.
Therefore, the environmental factors necessary for the growth of plants include:
i. adequate sunlight, water and carbon dioxide (for
photosynthesis).
ii. mineral salts (for synthesis of proteins, enzymes and other
essential substances in the body).
39
iii. warm temperature (for enzymes to catalyze reactions at a
suitable speed) e.g. optimum temperature for man is 370C.
iv. oxygen for respiration
Environmental factors necessary for the growth of animals include
i. balanced diet (adequate amounts of carbohydrates, lipids,
proteins, mineral salts, vitamins and water).
ii. Oxygen iii. Warmth (or suitable temperature).
Cell enlargement and differentiation
Cell division is usually followed by cell enlargement and cell differentiation. For instance, of the cells
formed by the cambium in a plant, some specialize into xylem, and some into phloem cells. Again,
all the cells in a human body come from one original cell, the zygote. However, as cell division
continues, some cells differentiate into nerve cells, others into bone cells others into skin cells,
muscle cells and so on.
Observing cell division
Material required
A variety of prepared slides of root tips, microscope.
Procedure
1.
Examine under the microscope, each of the slides provided.
2.
Make a high power magnification drawing of as many of the cells as you require to give you
a complete story of the process of cell division or mitosis.
40
Environmental Factors that affect growth
Several environmental factors affect growth. You may have observed that many plants grow
faster in the rainy season, when water is available in adequate amounts than in the dry season
e.g. mango plant. In the dry season, the shoots of some plants die, and the plants survive the
dry season by means of seeds (e.g. cowpea, maize) or underground parts e.g. yam, cocoyam.
Growth requires synthesis of new protoplasm and other body materials such as cellulose (in
plants). Food is necessary for synthesis of protoplasm and body materials. Energy obtained
through respiration is also necessary for synthesis of body materials.
Therefore, the environmental factors necessary for the growth of plants include:
i. adequate sunlight, water and carbon dioxide (for
photosynthesis).
ii. mineral salts (for synthesis of proteins, enzymes and other
essential substances in the body).
iii. warm temperature (for enzymes to catalyze reactions at a
suitable speed) e.g. optimum temperature for man is 370C.
iv. oxygen for respiration
Environmental factors necessary for the growth of animals include
i. balanced diet (adequate amounts of carbohydrates, lipids,
proteins, mineral salts, vitamins and water).
ii. Oxygen iii. Warmth (or suitable temperature).
41
GROWTH
Definition: growth is defined as an irreversible increase in size and complexity of an organism
brought about by the synthesis of new protoplasm. For growth to occur, the rate of synthesis or
building up of materials (anabolism) must exceed the rate of breaking down (catabolism).
Growth in plants is indefinite and apical while growth in animals is definite and uniform in all
parts of the body.
Basis for Growth
For any organism to grow, it must pass through three phases usually referred to as the basis
of growth. These are:
(i)
Cell division: Cell division involves cell multiplication. In order to multiply,
the cells undergo certain divisions. One cell divides into two, two into four,
four into eight and so on. Two types of cell division exist, according to the
behaviour of chromosomes. These are mitosis and meiosis.
(ii)
Cell enlargement: this is the process which follows cell division in which the
daughter cells increase in mass and in size. That is, it enlarges in size.
(iii)
Cell differentiation: This takes place after cell enlargement in which each
cell develops into a special type of cell by changing its shape and structure in
order to carry out a specialized or a particular function. The kind of cell it
becomes depends on its position in the body of the organism. For example, in
human body, a cell may develop into a nerve cell if it is the brain. Cell
differentiation is important in the growth and development of mature
multicellular organisms.
Types of Cells Division
(a)
Mitosis
Meaning: Mitosis is a cell or nuclear division following the duplication of the chromosomes, whereby
each daughter cell or nucleus has exactly the same chromosome content as the parent. In other
words, mitosis is a cell division in which daughter cells have the same number of chromosomes as
the parent cell.
Mitosis takes place in somatic cells, i.e. body cells that are not involved in the production of
gametes. Mitosis takes place during an organism’s growth, development and asexual reproduction.
42
In animals, mitosis takes place in the terminal bud of the shoot, at the tip of the roots and shoots. In
animals, mitosis occurs at growth centres which are everywhere.
Mitosis produces diploid cells. In order words, the number of chromosomes in each somatic cell of
an organism is called the diploid number (2n).
Stages of Mitosis
There are five stages or phases of mitosis these are:
(1)
Interphase: this is the latent or resting stage of the cell. At this stage, the cell has
normal appearance of non-dividing cell condition. Chromosomes are too threadlike for clear visibility.
(2)
Prophase: the prophase is divided into two: early and late prophase. During early
prophase, the chromosomes become visible as they contracted and nucleolus
shrinks. Centrioles are formed at opposite sides of the nucleus. Spindle fibres start
to form and during the late prophase, the chromosomes becomes shorter and
fatter. Each is seen to consist of a pair of chromatids jointed at the centromere and
nucleus disappears. Prophase ends with the breakdown of nuclear membrane.
(3)
Metaphase: Metaphase also exists in early and late forms. During early
metaphase, the chromosomes arranged themselves on the equator of the spindle
and at late metaphase, the chromatids draw apart at the centromere region.
(4)
Anaphase: Anaphase also exists in early and late forms. During early anaphase,
the chromatids part company and migrate to opposite poles of cell while during
late anaphase, the chromosomes reach their destination, i.e., toward the poles.
(5)
Telophase: Telophase stages are equally divided into early and late forms. During
the early telophase, the cell starts to constrict across the middle. During late
telophase, the constriction continues. The nulear membrane and nucleolus reform
in each daughter cell. Spindle apparatus degenerates. The chromosomes
eventually regain their thread like form and the cell returns to resting condition.
(i.e. Interphase).
43
Stages in Mitosis
44
Importance or Role of Mitosis
(i)
Growth, development or specialization takes place as a result of mitosis.
(ii)
Repair of cells are possible through mitosis.
(iii)
Mitosis ensures exact copy of DNA or sum total of inherited factors or genes are
transmitted to the daughter cell or it ensure consistency of DNA configuration.
(iv)
Mitosis also is the basis for asexual reproduction, e.g. binary and multiple fission of
Amoeba.
Life Process Involved in Mitosis
Life examples of mitotic process include:
(i)
Formation of new cells in the malphigian layer of the skin,
(ii)
Production of red blood and white blood cells in the bone marrow,
(iii) Cell division in liver,
(iv) Cell division in meristem or tip of root or in cambium,
(v)
Binary fission,
(vi) Growth in spermatogenesis,
(vii) Repair or healing of wound.
Aspect of Growth
It is sometimes very difficult to determine growth in organism. Growth varies from one organism to
another. Parameters normally used to measure growth in organisms include:
(i)
Mass (ii) length, height or width (iii) area or volume.
In most growth studies, mass may be measured as wet mass and dry mass.
(i)
Wet mass: wet mass is the mass of the organisms under normal conditions. It is not a
reliable indication of growth.
(ii)
Dry mass: Dry mass is the mass of an organism after all the water in it has been
removed. Although measuring growth in terms of dry mass is an accurate and reliable
method, the organisms gets killed in the process. This means, it is not possible to
measure growth in the same organism. To study growth by measuring dry mass, we
must carry out the study on a large number of similar organisms. Growth can then be
estimated by removing a given number of organisms at a time and estimating their dry
weight.
45
(b)
Size and length: size and length can be measured at successive intervals on the same
organism, e.g. height of man, length of snake etc.
(c)
Increase in number of cell: increase in the number of cells is also a proof of growth
of a population. A popular example of growth in organisms is the yeast. The yeast cell
is capable of budding or dividing into two, two into four and four into eight etc. the
yeast culture continues to double its number as long as non of the cells dies or losses
its power of division.
Regions of Fastest Growth in Plants
The regions of fastest growth in plants are the root and stem apices. In the root, the root tip
is a region where the cells are dividing rapidly. The root and stem apices of a plant can be divided
into the region of cell elongation and the region of cell maturation.
Growth in Root Apex
The region of cell division is also known as the apical meristem. It consists of meristematic
cells. i.e. cells capable of active division. The root tip is covered by the root cap.
46
In the region of cell elongation, the cell becomes enlarged to their maximum size by the
stretching of their ways. The cells in the region of maturation attain their permanent size and
become specialized to carry out certain functions.
Note: The stem apices include the terminal buds and lateral or axillary buds.
Apical meristems bring about the growth in length (height) of the plant. In shoot, they also
give rise to branches, leaves and flowers. Apical meristems bring about primary growth (the first
growth) of a plant.
Determination of Fastest Growth Regions in the Root
A young germinating seedling is taken and its radical is marked with Indian ink at interval of
2mm.The seedling is then pinned onto a cork and is placed in a bottle containing some water. The
experiment is left in a dark room for about eight hours.
To Determine the Rate of Growth of a Root
Then, the seedling is taken out and the distances between successive ink marks are
measured. The difference between the length of each new interval and an old interval (i.e. 2mm)
would give the increase in the length of that interval in eight hours. From this, the rate of growth of
the root can be calculated.
47
Factors Affecting Growth
Factors which affect the growth of organisms are grouped into two parts which are:
(a)
External factors which include availability of nutrients, humility, light, temperature,
PH and accumulation of metabolic product;
(b)
Internal factors which include the hormones.
External Factors
(1)
Availability of Nutrients: all living organisms require nutrients or food and water
which are necessary for the normal growth and development of the body.
(2)
Humidity: all living things also require certain level of humidity to enable them
grow. Too low or too high of it will affect growth.
(3)
Light: most plants require the presence of sunlight to enable them carry out
photosynthesis. It is from this source that they derive their energy and food. Most
animal, bacteria and fungi can live in darkness and grow in their habitat.
(4)
Temperature: All metabolic processes are accelerated at a certain level of
temperature. Too low or too high a temperature can adversely retard major processes
in the body.
(5)
PH: the PH of the fluid in contact with a cell has a profound effect on all its activities.
Growth can be hampered at certain level of acidity or alkalinity.
(6)
Accumulation of Metabolic Products: Most metabolic products which accumulate
within the body can affect growth. Excessive accumulation is toxic or harmful to the
body system and will eventually retard growth.
Internal Factors
(7)
Hormones: Hormones are internal factors which are known to affect the growth of
plants and animals. Plant hormones which affect the growth of plants are auxins and
gibberellins. Auxins promote or inhabit cell elongation in stems and roots. They also
stimulate cell division.
Gibberellins promote cell elongation and bring about growth in the stem. They also affect
cell division and cell differentiation to a certain extent.
In animals, hormones are secreted by endocrine glands. The hormones mainly concerned
with growth are secreted by anterior pituitary gland, the thyroid gland and the gonads; abnormal
48
growth in humans, like dwaftism or gigantism is due to errors in the secretion of one of these
hormones.
Cell Reaction to its Environment
All living things are capable of responding to internal and external stimuli. The ability to do this is
called irritability or sensitivity. By this means, plants and animal are able to detect and respond to
changes in their environment irritability is one of the basic characteristics of living organism.
Types of Response
Generally, animals’ response very quickly to external stimuli while plants respond slowly.
Again, only certain organs respond to external stimuli in plants but in animals, often, the whole
organism respond to the stimulus. There are three major types of responses. These are tactic, nastic
and tropic movements.
Taxis or Tactic Movements
Meaning: taxis or tactic response is a directional type of response or movement which a whole
organism moves from one place to another in response to external stimuli such as light,
temperature, water or certain chemicals.
Stimuli
(i)
Light
Name of response
Example
Phototaxis
Euglena and chlamydomonas swim
towards light of low intensity
(positive phototaxis) and away from
light intensity (negative phototaxis)
(ii)
Chemotaxis
Chemotaxis
In a moss plant, sperms swim
towards the chemical by the egg cell
(positive phototaxis).
(iii)
Temperature
Thermotaxis
Motile bacterias swim from cold
regions to warm region (positive
thermotaxis).
Nastism or Nastic Movement
Meaning: Nastism is a type of response in which a part of a plant moves in response to nondirectional stimuli such as changes in light intensity, temperature or humidity.
49
The response movements are also non-directional. Example of nastic movement is:
i.
Closing of the morning glory flower when the light intensity is low.
ii.
The petals of sunflower which open in the light and close in the dark.
iii.
The folding of the leaflets of the mimosa plant when it is touched,
iv.
The closing of the leaflets of the flamboyant tree i.e. sleeping movements due to
low light intensity.
Tropism or Tropic Movement
Meaning: tropism is type of response in which a part of a plant moves in response to a directional
stimulus. The direction of the response is related to that of the stimulus and is Importance or Role
of Mitosis
(v)
Growth, development or specialization takes place as a result of mitosis.
(vi)
Repair of cells are possible through mitosis.
(vii) Mitosis ensures exact copy of DNA or sum total of inherited factors or genes are
transmitted to the daughter cell or it ensure consistency of DNA configuration.
(viii) Mitosis also is the basis for asexual reproduction, e.g. binary and multiple fission of
Amoeba.
Life Process Involved in Mitosis
Life examples of mitotic process include:
(viii) Formation of new cells in the malphigian layer of the skin,
(ix) Production of red blood and white blood cells in the bone marrow,
(x)
Cell division in liver,
(xi) Cell division in meristem or tip of root or in cambium,
(xii) Binary fission,
(xiii) Growth in spermatogenesis,
(xiv) Repair or healing of wound.
Aspect of Growth
It is sometimes very difficult to determine growth in organism. Growth varies from one organism to
another. Parameters normally used to measure growth in organisms include:
(ii)
50
Mass (ii) length, height or width (iii) area or volume.
In most growth studies, mass may be measured as wet mass and dry mass.
(iii)
Wet mass: wet mass is the mass of the organisms under normal conditions. It is not a
reliable indication of growth.
(iv)
Dry mass: Dry mass is the mass of an organism after all the water in it has been
removed. Although measuring growth in terms of dry mass is an accurate and reliable
method, the organisms gets killed in the process. This means, it is not possible to
measure growth in the same organism. To study growth by measuring dry mass, we
must carry out the study on a large number of similar organisms. Growth can then be
estimated by removing a given number of organisms at a time and estimating their dry
weight.
(d)
Size and length: size and length can be measured at successive intervals on the same
organism, e.g. height of man, length of snake etc.
(e)
Increase in number of cell: increase in the number of cells is also a proof of growth
of a population. A popular example of growth in organisms is the yeast. The yeast cell
is capable of budding or dividing into two, two into four and four into eight etc. the
yeast culture continues to double its number as long as non of the cells dies or losses
its power of division.
Regions of Fastest Growth in Plants
The regions of fastest growth in plants are the root and stem apices. In the root, the root tip
is a region where the cells are dividing rapidly. The root and stem apices of a plant can be divided
into the region of cell elongation and the region of cell maturation.
51
Growth in Root Apex
The region of cell division is also known as the apical meristem. It consists of meristematic
cells. i.e. cells capable of active division. The root tip is covered by the root cap.
In the region of cell elongation, the cell becomes enlarged to their maximum size by the
stretching of their ways. The cells in the region of maturation attain their permanent size and
become specialized to carry out certain functions.
Note: The stem apices include the terminal buds and lateral or axillary buds.
Apical meristems bring about the growth in length (height) of the plant. In shoot, they also
give rise to branches, leaves and flowers. Apical meristems bring about primary growth (the first
growth) of a plant.
Determination of Fastest Growth Regions in the Root
52
A young germinating seedling is taken and its radical is marked with Indian ink at interval of
2mm.The seedling is then pinned onto a cork and is placed in a bottle containing some water. The
experiment is left in a dark room for about eight hours.
To Determine the Rate of Growth of a Root
Then, the seedling is taken out and the distances between successive ink marks are
measured. The difference between the length of each new interval and an old interval (i.e. 2mm)
would give the increase in the length of that interval in eight hours. From this, the rate of growth of
the root can be calculated.
Factors Affecting Growth
Factors which affect the growth of organisms are grouped into two parts which are:
(c)
External factors which include availability of nutrients, humility, light, temperature,
PH and accumulation of metabolic product;
(d)
Internal factors which include the hormones.
External Factors
53
(8)
Availability of Nutrients: all living organisms require nutrients or food and water
which are necessary for the normal growth and development of the body.
(9)
Humidity: all living things also require certain level of humidity to enable them
grow. Too low or too high of it will affect growth.
(10)
Light: most plants require the presence of sunlight to enable them carry out
photosynthesis. It is from this source that they derive their energy and food. Most
animal, bacteria and fungi can live in darkness and grow in their habitat.
(11)
Temperature: All metabolic processes are accelerated at a certain level of
temperature. Too low or too high a temperature can adversely retard major processes
in the body.
(12)
PH: the PH of the fluid in contact with a cell has a profound effect on all its activities.
Growth can be hampered at certain level of acidity or alkalinity.
(13)
Accumulation of Metabolic Products: Most metabolic products which accumulate
within the body can affect growth. Excessive accumulation is toxic or harmful to the
body system and will eventually retard growth.
Internal Factors
(14)
Hormones: Hormones are internal factors which are known to affect the growth of
plants and animals. Plant hormones which affect the growth of plants are auxins and
gibberellins. Auxins promote or inhabit cell elongation in stems and roots. They also
stimulate cell division.
Gibberellins promote cell elongation and bring about growth in the stem. They also affect
cell division and cell differentiation to a certain extent.
In animals, hormones are secreted by endocrine glands. The hormones mainly concerned
with growth are secreted by anterior pituitary gland, the thyroid gland and the gonads; abnormal
growth in humans, like dwaftism or gigantism is due to errors in the secretion of one of these
hormones.
Cell Reaction to its Environment
All living things are capable of responding to internal and external stimuli. The ability to do this is
called irritability or sensitivity. By this means, plants and animal are able to detect and respond to
changes in their environment irritability is one of the basic characteristics of living organism.
54
Types of Response
Generally, animals’ response very quickly to external stimuli while plants respond slowly.
Again, only certain organs respond to external stimuli in plants but in animals, often, the whole
organism respond to the stimulus. There are three major types of responses. These are tactic, nastic
and tropic movements.
Taxis or Tactic Movements
Meaning: taxis or tactic response is a directional type of response or movement which a whole
organism moves from one place to another in response to external stimuli such as light,
temperature, water or certain chemicals.
Stimuli
(iv)
Light
Name of response
Example
Phototaxis
Euglena and chlamydomonas swim
towards light of low intensity
(positive phototaxis) and away from
light intensity (negative phototaxis)
(v)
Chemotaxis
Chemotaxis
In a moss plant, sperms swim
towards the chemical by the egg cell
(positive phototaxis).
(vi)
Temperature
Thermotaxis
Motile bacterias swim from cold
regions to warm region (positive
thermotaxis).
Nastism or Nastic Movement
Meaning: Nastism is a type of response in which a part of a plant moves in response to nondirectional stimuli such as changes in light intensity, temperature or humidity.
The response movements are also non-directional. Example of nastic movement is:
v.
Closing of the morning glory flower when the light intensity is low.
vi.
The petals of sunflower which open in the light and close in the dark.
vii.
The folding of the leaflets of the mimosa plant when it is touched,
viii.
The closing of the leaflets of the flamboyant tree i.e. sleeping movements due to
low light intensity.
55
Tropism or Tropic Movement
Meaning: tropism is type of response in which a part of a plant moves in response to a directional
stimulus. The direction of the response is related to that of the stimulus and is
56