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SULPHUR AND ITS COMPOUND SULPHUR AND ITS COMPOUND:A.SULPHUR (S) Sulphur is an element in Group VI(Group 16)of the Periodic table . It has atomic number 16...






INTRODUCTION TO BIOLOGY ,Biology derived from Greek words-BIOS meaning LIFE and LOGOS meaning STUDY or KNOWLEDGE.

  • Biology means “life knowledge”.
  • It is the study of living things/organisms.

Branches of Biology

  • Botany – study of plants.
  • Zoology – study of animals.
  • Microbiology – study’ of microscopic organisms.
  • Morphology – study of external structure of organisms.
  • Anatomy – study of internal structure of organisms.
  • Physiology – study of the functioning or working of the cells or body.
  • Biochemistry – study of the chemistry of materials in living organisms.
  • Cytology – study of cells.
  • Genetics – study of inheritance.
  • Ecology- study of the relationship between organisms and their environment.
  • Taxonomy – sorting out of organisms into groups.
  • Histology – study of fine structure of tissues.
  • Virology – study of viruses.
  • Bacteriology – study of bacteria.
  • Entomology – study of insects.
  • Ichthyology – study of fish.
  • Ornithology-study of birds

Importance of Biology

  • One learns about the functioning of the human body.
  • One understands the developmental changes that take place in the body.
  • It contributes immensely to improved life.
  • It enables one to enter careers such as:
  • Medicine,
  • Nutrition,
  • Public Health,
  • Dentistry,
  • Agriculture
  • Environmental Studies.
  • Teaching

Characteristics of Living Things

Life defined through observations of activities carried out by living things;

  • Nutrition 
    1. Nutrition is the processes by which food/nutrients are acquired/made and utilized by living organisms.
    2. Green plants and certain bacteria make their own food.
    3. All other organisms feed on complex organic materials.
  • Respiration 
  • This is the breakdown of food to provide energy.
  • The energy released is used for various activities in the organism.
  • Gaseous Exchange Process throw which respiratory gases(CO2&O2) are taken in and out through a respiratory surface.
  • Excretion 
  • Excretion is the removal of metabolic wastes from the body.
  • Substances like urea, carbon dioxide (Carbon (IV) oxide).
  • These substances are poisonous if allowed to accumulate in the body.
  • Growth and Development 
  • Growth means irreversible change in size.
  • All organisms increase in size that is, they grow.
  • Development is irreversible change in complexity.
  • As they do so, they also become differentiated in form.
  • Reproduction-Reproduction is the formation of new individuals of a species to ensure continued existence of a species and growth of its population.
  • Irritability 
  • The ability of organisms to detect and respond to changes in the environment. This is of great survival value to the organism.
  • Movement 
  • Is the progressive change in position from one place to another.
  • Some organisms are sessile (i.e. fixed to the substratum).
  • The majority of plants move only certain parts.


Collection and Observation of Organisms

Biology as a practical subject is learnt through humane handling of organisms.

Materials needed for collection of organisms:-

  • Knives to cut portions of plant stem/root or uproot.
  • Polythene bags to put the collected plant or specimens.
  • Insect collecting jars.
  • Insect killing jars.
  • Hand gloves.
  • Sweep nets
  •  Pooters
  • Traps

Observation of Organisms

  • Observe the plant/animal in its natural habitat before collecting.
  • Identify the exact place -on surface, under rock, on tree trunk, on branches.
  • What does it feed on?
  • How does it interact with other animals and the environment?
  • How many of that kind of plant or animal are in a particular place?
  • Plant specimens placed on the bench and sorted out into;- seeds/stems/roots/leaves/fruits.
  • Animal specimens may be left inside polythene bags if transparent.
  • Others (killed ones) are put in petri­
  • Use hand lens to observe the external features of small animals.

Presenting the Results of Observations

  • Organisms are observed and important features noted down: colour, texture ­hard or soft; if hairy or not. Size is measured or estimated.
  • Biological Drawings – It is necessary to draw some of the organisms.
  • In making a biological drawing, magnification (enlargement) is noted.
  • Indicate the magnification of your drawing.
  • e how many times the drawing is larger/smaller than the actual specimen MG=length of drawing/length specimen

How to Draw

  • Several drawings of one organism may be necessary to represent all features observed, e.g.
  • Anterior view of grasshopper shows all mouth parts properly, but not all limbs.
  • Lateral (side) view shows all the legs.


Collection, Observation and Recording of Organisms


  • Plants and animals collected from the environment, near school or within school compound using nets, bottles and gloves.
  • Animals collected include:-arthropods, earthworms and small vertebrates like lizards/chameleons/ rodents.
  • Place in polythene bags and take to the laboratory.
  • Stinging/poisonous insects killed using ether.
  • Other animals are observed live and returned to their natural habitat.
  • Plant specimen collected include:- leaves, flowers and whole plants.
  • Observations are made to show the following:-
  • Plants have roots, stems, leaves and flowers.
  • Animals have legs, hair, hard outer covering, feathers, eyes, mouth, limbs and other appendages,

The differences between animals and plants collected.

Comparison Between Plants And Animals

Plants   Animal
l. Plants are fixed in position and do not” move. l. Most animals move in search of food, shelter  and mates.
2. Respond slowly to stimuli. 2. Respond quickly to stimuli.
3. Cells have cellulose cell walls. 3. Cells have no cell walls only a cell membrane
4. Plants make their own food from simple materials such as CO2 and water using light energy 4. Animals feed on already made food.










Classification I


  • Classification is putting organisms into groups.
  • Classification is based on the study of external characteristics of organisms.
  • It involves detailed observation of structure and functions of organisms.
  • Organisms with similar characteristics are put in one group.
  • Differences in structure are used to distinguish one group from another.
  • The magnifying lens is an instrument that assists in the observation of fine structure e.g. hairs by enlarging them

Using a Magnifying Lens

  • A specimen is placed on the bench or held by hand,
  • Then the magnifying lens is moved towards the eye until the object is dearly focused and an enlarged image is seen.
  • The magnification can be worked out as follows:

length of the drawing

Magnification = length of the specimen

  • Note: magnification has no units.

Nececity/need for Classification

  • To be able to identify organisms into their taxonomic groups.
  • To enable easier and systematic study of organisms.
  • To show evolutionary relationships in organisms.

Major Units of Classification (Taxonomic Groups)

  • Taxonomy is the study of the characteristics of organisms for the purpose of classifying them.
  • The groups are Taxa (singular Taxon).

The taxonomic groups include:

  • Species: This is the smallest unit of classification. Organisms of the same species resemble each other. The number of chromosomes in their cells is the same. Members of a species interbreed to produce fertile offspring.
  • Genus (plural genera): A genus is made up of a number of species that share several characteristics. Members of a genus cannot interbreed and if they do, the offspring are infertile.
  • Family: A family is made up of a number of genera that share several characteristics.
  • Order: A number of families with common characteristics make an order.
  • Class: Orders that share a number of characteristics make up a class.
  • Phylum/Division: A number of classes with similar characteristics make up a phylum (plural phyla) in animals. In plants this is called a division.
  • Kingdom: This is made up of several phyla (in animals) or divisions (in plants). It is the largest taxonomic unit in classification.



Living organisms are classified into five kingdoms;

  • Monera,
  • Protoctista,
  • Fungi,
  • Plantae

Kingdom Fungi

  • Some are unicellular while others are multicellular.
  • They have no chlorophyll.
  • Most are saprophytic e.g. yeasts, moulds and mushrooms.
  • A few are parasitic e.g. Puccinia graminae.

Kingdom Monera (Prokaryota)

  • These are very small unicellular organisms.
  • They lack a nuclear membrane
  • do not have any bound membrane organelles.
  • Hence the name Prokaryota.
  • They are mainly bacteria, e.g. Vibrio cholerae.

Kingdom Protoctista

  • They are unicellular organisms.
  • Their nucleus and organelles are surrounded by membranes (eukaryotic).
  • They include algae, slime moulds – fungi-like and protozoa

 Kingdom Plantae

  • They are all multicellular.
  • They contain chlorophyll and are all autotrophic.
  • They include; Bryophyta (mossplant), Pteridophyta (ferns) and Spermatophyta (seed bearing plants).

Kingdom Animalia

  • These are all multicellular and heterotrophic.
  • Examples are annelida (earthworms), mollusca (snails),athropoda, chordata .
  • Example of Arthropods are ticks, butterflies.
  • Members of Chordata are fish, frogs and humans.

External Features of Organisms

In plants we should look for:-

  • Spore capsule and rhizoids in moss plants.
  • Sori and fronds in ferns.
  • Stem, leaves, roots, flowers, fruits and seeds in plants.

 In animals, some important features to look for are:

  • Segmentation, presence of limbs and, number of body parts, presence and number of antennae. These are found in phylum arthropoda:
  • Visceral clefts, notochord, nerve tube, fur or hair, scales, fins, mammary glands, feathers and wings.
  • These are found in chordata.

Binomial Nomenclature

  • Organisms are known by their local names.
  • Scientists use scientific names to be able to communicate easily among themselves.
  • This method of naming uses two names, and is called Binomial nomenclature.
  • The first name is the name of the genus: (generic name) which starts with a capital letter.
  • The second name is the name of the species (specific name) which starts with a small letter.
  • The two names are underlined or written in italics.
  • Man belongs to the genus Homo, and the species,
  • The scientific name of man is therefore Homo
  • Maize belongs to the genus Zea, and the species mays.
  • The scientific name of maize is Zea


Practical Activities

  • Use of Collecting Nets, Cutting Instruments and Hand Lens.
  • Forceps are used to collect crawling and slow moving animals.
  • Sweep nets are used to catch flying insects.
  • Cutting instrument like scapel is used to cut specimen e.g. making sections.
  • Hand lens is used to magnify small plants and animals.
  • Drawing of the magnified organism are made and the linear magnification of each calculated.

Collection and Detailed Observation of Small Plants and Animals

e.g. moss, ferns, bean.

Look for the following:

  • Moss plants: Rhizoids and spore capsules.
  • Fern plants: Rhizomes with adventitious roots; large leaves (fronds) with Sori (clusters of sporangia).
  • Seed plants: Tree/shrub (woody) or non-woody (herbs) e.g. bean.
  • Root system – fibrous, adventitious and tap root.
  • Stem – position and length of interrnodes.
  • Type of leaves – simple or compound; arranged as alternate, opposite or whorled.
  • Flower – colour, number of parts, size and relative position of each:
  • Fruits – freshy or dry; edible or not edible.
  • Seeds – monocotyledonous or dicotyledonous.

Small animals e.g. earthworms, tick, grasshopper, butterfly, beetles.

Observe these animals to see:

  • Number of legs.
  • Presence or absence of wings.
  • Number of antennae.
  • Body covering.
  • Body parts.



  • The cell is the basic unit of an organism.
  • All living organisms are made up of cells.
  • Some organisms are made up of one cell and others are said to be multicellular.
  • Other organisms are made of many cells and are said to be multicellular.
  • Cells are too little to see with the naked eye.
  • They can only be seen with the aid of a microscope.

The microscope

The microscope is used to magnify objects.


  • The magnifying power is usually inscribed on the lens.
  • To find out how many times a specimen is magnified, the magnifying power of the objective lens is multiplied by that of the eye piece lens.
  • If the eye piece magnification lens is x10 and the objective lens is x4, the total magnification is x40.
  • Magnification has no units.
  • It should always have the multiplication sign.e.g.x40

   Microscope parts and their functions

Parts   Function(s)
Eye piece Has a lens which contributes to the magnification of the object under view.
Coarse adjustment knob Moves the body tube up and down for long distances and it brings the image
into focus.
Fine adjustment knob Moves the body tube and brings the image into fine focus.
Body tube Ji Holds the eye piece and the revolving nose piece. It directs light from
objective lenses to the eye piece lens.
Revolving nose piece Holds and brings objective lenses into position.
Objective lens Contributes to the magnification of the object.
Arm/limb It is for handling the microscope and also tilting it.
Stage Is the flat platform onto which the slide with the object is placed.
Clips They hold the slide firmly onto the stage.
Condenser Concentrates light onto the object.
Diaphragm ~egulates the amount of light passing through the object.
Mirror Reflects light into the condenser.
Hinge screw Fixes the arm to the base and allows for tilting of the arm.
Base/stand Provides support to the microscope.


To View the Object

  • Turn the low power objective lens until it clicks into position.
  • Looking through the eye piece, ensure that enough light is passing through by adjusting the mirror.
  • This is indicated by a bright circular area known as the field of view.
  • Place the slide containing the specimen on stage and clip it into position.
  • Make sure that the specimen is in the centre of the field of view.
  • Using the coarse adjustment knob, bring the low power objective lens to the lowest point.
  • Turn the knob gently until the specimen comes into focus.
  • If finer details are required, use the fine adjustment knob.
  • When using high power objective always move the fine adjustment knob upwards.

Care of a Microscope

  • Great care should be taken when handling it.
  • Keep it away from the edge of the bench when using it.
  • Always hold it with both hands when moving it in the laboratory.
  • Clean the lenses with special lens cleaning paper.
  • Make sure that the low power objective clicks in position in line with eye piece lens before and after use.
  • Store the microscope in a dust-proof place free of moisture.

Cell Structure as Seen Through the Light Microscope

The cell as seen above has the following:

Cell membrane (Plasma membrane):

  • This is a thin membrane enclosing cell contents.
  • It controls the movement of substances into and out of the cell.


  • This is a jelly-like substance in which chemical processes are carried out.
  • Scattered all over the cytoplasm are small structures called organelles.
  • Like an animal cell, the plant cell has a cell membrane, cytoplasm and a nucleus.


  • Plant cells have permanent, central vacuole. It contains cell sap where sugars and salts are stored.

Cell wall:

  • This is the outermost boundary of a plant cell.
  • It is made of cellulose.
  • Between the cells is a middle lamella made of calcium pectate.


  • With special staining techniques it is possible to observe chloroplasts.
  • These are structures which contain chlorophyll, the green pigment responsible for trapping light for photosynthesis.

The Electron Microscope (EM)

  • Capable of magnifying up to 500,000 times.
  • The specimen is mounted in vacuum chamber through which an electron beam is directed.
  • The image is projected on to a photographic plate.
  • The major disadvantage of the electron microscope is that it cannot be used to observe living objects.
  • However, it provides a higher magnification and resolution (ability to see close points as separate) than the light microscope so that specimen can be observed in more detail.

Cell Structure as Seen Through Electron Microscope

 The Plasma Membrane

  • Under the electron microscope, the plasma membrane is seen as a double layer.
  • This consists of a lipid layer sandwiched between two protein layers.
  • This arrangement is known as the unit membrane and the shows two lipid layers with proteins within.
  • Substances are transported across the membrane by active transport and diffusion.

The Endoplasmic Reticulum (ER)

  • This is a network of tubular structures extending throughout the cytoplasm of the cell.
  • It serves as a network of pathways through which materials are transported from one part of the cell to the other.
  • An ER encrusted with ribosomes it is referred to as rough endoplasmic reticulum.
  • An ER that lacks ribosomes is referred to as smooth endoplasmic reticulum.
  • The rough endoplasmic reticulum transports proteins while the smooth endoplasmic reticulum transports

The Ribosomes

  • These are small spherical structures attached to the ER.
  • They consist of protein and ribonucleic acid (RNA).
  • They act as sites for the synthesis of proteins.

Goigi Bodies

  • Golgi bodies are thin, plate-like sacs arranged in stacks and distributed randomly in the cytoplasm.
  • Their function is packaging and transportation of glycol-proteins.
  • They also produce lysosomes.



  • Each mitochondrion is a rod-shaped organelle.
  • Made up of a smooth outer membrane and a folded inner membrane.
  • The foldings of the inner membrane are called
  • They increase the surface area for respiration.
  • The inner compartments called the matrix.
  • Mitochondria are the sites of cellular respiration, where energy is produced.


  • These are vesicles containing hydrolytic enzymes.
  • They are involved in the breakdown of micro-organisms, foreign macromolecules and damaged or worn-out cells and organelles ..

The Nucleus

  • The nucle s is surrounded by a nuclear membrane which is a unit membrane.
  • The nuclear membrane has pores through which materials can move to the surrounding cytoplasm.
  • The nucleus contains proteins and nucleic acid deoxyribonucleic acid (DNA) and RNA.
  • The chromosomes are found in the nucleus.
  • They are the carriers of the genetic information of the cell.
  • The nucleolus is also located in the nucleus but it is only visible during the non-dividing phase of the cell.

The Chloroplasts

  • These are found only in photosynthetic cells.
  • Each chloroplast consists of an outer unit. membrane enclosing a series of interconnected membranes called lamellae.
  • At various points along their length the lamellae form stacks of disc like structures called grana.
  • The lamellae are embedded in a granular material called the stroma.
  • The chloroplasts are sites of photosynthesis.
  • The light reaction takes place in the lamellae while the dark reactions take place in the stroma.

 Comparison between animal cell and plant cell

Plant Cell         Animal Cell
Has a cell wall and a cell membrane. · Has cell membrane only.
Nucleus at periphery. Nucleus at the center.
Have chloroplasts. Have no chloroplasts.
Has a large central vacuole. · Has no vacuoles, they are small and scattered.
Are usually large. Are usually small.
Are regular in shape. Irregular in shape.
Has no centriole. Has centrioles.
Stores starch, oils and protein. Store glycogen and fats.


Cell Specialisation

Cells are specialised to perform different functions in both plants and animals.


  • Palisade cells have many chloroplasts for photosynthesis.
  • Root hair cells are long and thin to absorb water from the soil.
  • Red blood cells have haemoglobin which transports oxygen.
  • Sperm cells have a tail to swim to the egg.
  • Multicellular organisms cells that perform the same function are grouped together to form a tissue.
  • Each tissue is therefore made up of cells that are specialised to carry out a particular function.


Animal Tissues- Examples of animal tissues

Type of Tissue Functions Characteristics
l. Epithelial Tissue Covering. allowing movement
of materials
(a) Squamous epithelium Covering of internal organs. lining for body cavity. Thin flat cells.
(b) Columnar epithelium Secretion. absorption e.g. in the alimentary canal. Cells that are longer than they are wide.
(c) stratified epithelium Covering surfaces, protection e.g. the skin. Several layers of epithelial cells (either
squamous. cuboidal or columnar).
(d) Cuboidal epithelium Absoption e.g. in the kidney tubules. cube like cells.
2. Muscular Tissue Contraction, bringing about movement of body parts. Contists of units called myofibrils.
(a) Striated (skeletal or Contract and allow movement. Are multicleated; have transverse striations;
voluntary muscle) controlled by voluntary nervous system.
(b) Smooth (visceral or cover internal organs; allow movement e.g. Are spindle-shaped. mononucleated;
involuntary muscle) peristalsis. controlled by involuntary nervous system.
(c) Cardiac muscle Cause contraction of the heart. contract rhythmically; are myogenic
(ability to contract is within)
3. Supporting Tissue Support the body. provide a rigid Cells that produce hard materials.
framework, protect soft tissue.
(a) Cartilage
(b) Bone
4. Blood Transport of materials. protection against disease. A complex tissue consisting of three types
of cells suspended in a fluid medium (Plasma)
5. Nerve Tissue Receive stimuli and transmit impulses; Consists of cells called neurones
co-ordinate body activities which are interconnected through
axons to enable transmission of impulses


 Plant Tissues

Example of plant tissues

Type of Tissue Functions Characteristics
L Meristematic Undergo division and cause growth, Small thin-walled celis, contain a
e.g. increase in length and girth lot of cytoplasm; found mostly at
the tip of shoots and roots.
2. Parenchyma Photosynthesis gaseous exchange; Thin walled cells; vary in shape
support; storage. and size; many intercellular
3. Collenchyma Strengthening. Thickened walls; no intercellular
spaces; found in cortex of stems.
4. Sclerenchyma Strengthening. Vary in shape; thick cell walls; are
usually dead.
5. Vascular Transport materials. Tubular vessels and trancheids
(a) Xylem Transport of water and mineral salts. joined end to end.
(b) Phloem Transport of organic materials Sieve elements joined to each other
(manufactured food). through sieve pores.



  • An organ is made up of different tissues
  • g. the heart, lungs, kidneys and the brain in animals and roots, stems and leaves in plants. 

Organ systems

  • Organs which work together form an organ system.
  • Digestive, excretory, nervous and circulatory in animals and transport and support system in plants.


  • Different organ systems form an organism.

 Practical Activities

Observation and Identification of parts of a light microscope and their functions

  • A light microscope is provided.
  • Various parts are identified and observed.
  • Drawing and labelling of the microscope is done.
  • Functions of the parts of the mircroscope are stated.
  • Calculations of total magnification done using the formula.

Eye piece lens maginification x objective lens rnaginification.

Preparation and Observation of Temporary Slides of Plant Cells

  • A piece of epidermis is made from the fleshy leaf of an onion bulb. It is placed on a microscope slide and a drop of water added.
  • A drop of iodine is added and a cover slip placed on top.
  • Observations are made, under low and medium power objective.
  • The cell wall and nucleus stain darker than other parts.
  • A labelled drawing is made.
  • The following are noted: Nucleus, cell wall, cytoplasm and cell membrane.

Observation of permanent slides of animal cells

  • Permanent slides of animal cells are obtained e.g, of cheek cells, nerve cells and muscle cells.
  • The slide is mounted on the microscope and observations made under low power and medium power objectives.
  • Labelled drawings of the cells are made.
  • A comparison between plant and animal cell is made.

Observation and Estimation of Cell Size and Calculation of Magnification of Plant Cells.

  • Using the low power objective, a transparent ruler is placed on the stage of the microscope.
  • An estimation of the diameter of the field of view is made in millimeters.
  • This is converted into micrometres (1mm=1000u)
  • A prepared slide of onion epidermal cells is mounted.
  • The cells across the centre of the field of view are counted from left and right and top to bottom.
  • The diameter of field of view is divided by the number of cells lying lengthwise to give an estimate of the length and width of each cell.

Cell Physiology

Meaning of cell physiology

  • The term physiology refers to the functions that occur in living organisms.
  • Cell physiology refers to the process through which substances move across the cell membrane.
  • Several physiological processes take place inside the cell.e.g. respiration.
  • Oxygen and glucose required enter the cell while carbon (IV) oxide and water produced leave the cell through the cell membrane.

Structure and properties of cell membrane

  • The cell membrane is the protective barrier that shelter cellular contents.
  • Movement of all substances into and out of the cells takes place across the cell membrane.
  • It is made up of protein and lipid molecules.
  • Lipid molecules have phosphate group attached to it on one end.
  • They are then referred to phospholipids.
  • The phospholipids are arranged to form a double layer.
  • The ends with phosphate group face outwards.
  • the proteins are scattered throughout the lipid double layer.
  • Some of these proteins act as carrier molecules that channel some material in and outside the cells.
  • The cell membrane allows certain molecules to pass through freely while others move through with difficulty and still others do not pass through at all.
  • This is selective permeability and the cell membrane is described as semi-permeable.


Properties of cell membrane


  • The cell membrane is semi-permeable.
  • it allows small molecules that are soluble in lipid to pass through with more ease than water soluble molecules.
  • this is due to the presence of the phospholipids double layer.


  • The cell membrane has electrical charges across its has positive charged ions on the outside and negatively charged ions on the inside.this property contributes to electrical impulses sent along nerve cells.
  • Sensitivity to changes in temperature and pH
  • Very high temperatures destroy the semi-permeability nature of the cell membrane because the proteins are denatured by extreme pH values have the same effect on the membrane permeability.
  • Physiological processes
  • Some of the physiological processes include diffusion, osmosis and active transport.


  • Diffusion is the movement of molecules or ions from a region of high concentration to a region of low concentration aided by a concentration gradient..
  • diffusion continues to occur as long as there is a difference in concentration between two regions (concentration gradient).
  • Stops when an equilibrium is reached i.e., when the concentration of molecules is the same in both regions.
  • Diffusion is a process that occurs inside living organisms as well as the external environment..
  • Does not require energy.

 Factors Affecting Diffusion

  • Concentration Gradient

An increase in the concentration of molecules at one region results in a steeper concentration gradient which in turn increases the rate of diffusion.

  • Temperature

High temperature increases kinetic energy of molecules. They move faster hence resulting in an increase in rate of diffusion, and vice versa.

  • Size of Molecules or Ions

The smaller the size of molecules or ions, the faster their movement hence higher rate of diffusion.

  • Density

The denser the molecules or ions diffusing, the slower the rate of diffusion, and vice versa.

  • Medium

The medium through which diffusion occurs also affects diffusion of molecules or ions. For example, diffusion of molecules through gas and liquid media is faster than through a solid medium.

  • Distance

This refers to the thickness or thinness of surface across which diffusion occurs. Rate of diffusion is faster when the distance is small i.e., thin surface.

  • Surface Area to Volume Ratio

The larger the surface area to volume ratio, the faster the rate of diffusion.

For example, in small organisms such as Amoeba the surface area to volume ratio, is greater hence faster diffusion than in larger organisms.

Role of Diffusion in Living Organisms

Some processes that depend on diffusion include the following:

  • Gaseous exchange: Movement of gases through respiratory surfaces is by diffusion.
  • Absorption of materials into cells Cells obtain raw materials and nutrients from the surrounding tissue fluid and blood through diffusion, e.g., glucose needed for respiration diffuses from blood and tissue fluid into cells.
  • Excretion: Removal of metabolic waste products like carbon (IV) oxide, and ammonia out of cells is by diffusion.
  • Absorption of the end-products of digestion from the intestines is by diffusion.


  • Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration through a semi-permeable membrane.
  • Osmosis is a special type of diffusion that involves the movement of water molecules only and not solute molecules.
  • Osmosis takes place in cells across the cell membrane as well as across non-living membranes
  • g. cellophane or visking tubing which are also semi-permeable,
  • It is purely a physical process.


Factors Affecting Osmosis

  • Size of solute molecules-

Osmosis’ occurs only when solute molecules are too large to pass through a semi-permeable membrane.

  • Concentration Gradient .

Osmosis occurs when two solutions of unequal solute concentration are separated by a semi-permeable membrane.

  • Temperature ,.

High temperatures increase movement of water molecules hence influence osmosis. However, too high temperatures denature proteins in cell membrane and osmosis stops.

  • Pressure

Increase in pressure affects movement of water molecules.

As pressure increases inside a plant cell, osmosis decreases.

Roles of Osmosis in Living Organisms

The following processes depend on osmosis in living organisms:

  • Movement of water into cells from the surrounding tissue fluid and also from cell to cell.
  • Absorption of water from the soil and into the roots of plants.
  • Support in plants especially herbaceous ones, is provided by turgor pressure, which results from intake of water by osmosis.
  • Absorption of water from the alimentary canal in mammals.
  • Re-absorption of water in the kidney tubules.
  • Opening and closing stomata.

Water Relations in Plant and Animal Cells

  • The medium (solution) surrounding cells or organisms is described by the terms hypotonic, hypertonic and
  • A solution whose solute concentration is more than that of the cell sap is said to be hypertonic.

A cell placed in such a solution loses water to the surroundings by osmosis.

  • A solution whose solute concentration is less than that of the cell sap is said to be hypotonic.

A cell placed in such a solution gains water from the surroundings by osmosis.

  • A solution which has the same solute concentration as the cell sap is said to be isotonic.

When a cell is placed in such a solution there will be no net movement of water either into or out of the cell.

Osmotic Pressure

  • The term osmotic pressure describes the tendency of the solution with a high solute concentration to draw water into itself when it is separated from distilled water or dilute solution by a semi-permeable membrane.
  • Osmotic pressure is measured by an osmometer.
  • When plant cells are placed in distilled water or in a hypotonic solution, the osmotic pressure in the cells is higher than the osmotic pressure of the medium.
  • This causes the water to enter the cells by osmosis.
  • The water collects in the vacuole which increases in size.
  • As a result the cytoplasm is pushed outwards and it in turn presses the cell membrane next to the cell wall.
  • This builds up water pressure (hydrostatic pressure) inside the cell.
  • When the cell is stretched to the maximum, the cell wall prevents further entry of water into the cell.
  • Then the cell is said to be fully
  • The hydrostatic pressure developed is known as turgor


  • When a plant cell is placed in a hypertonic medium, it loses water by osmosis.
  • The osmotic pressure of the cell is lower than that of the medium.
  • The vacuole decreases in size and the cytoplasm shrinks as a result of which the cell membrane loses contact with the cell wall.
  • The cell becomes flaccid. The whole process is described as plasmolysis.
  • Incipient plasmolysis is when a cell membrane just begins to lose contact with the cell wall.
  • Plasmolysis can be reversed by placing the cell in distilled water or hypotonic solution.
  • However, full plasmolysis may not be reversed if cell stays in that state for long.



  • The term wilting describes the drooping of leaves and stems of herbaceous plants after considerable amounts of water have been lost through transpiration.
  • It is observed in hot dry afternoons or in dry weather.
  • This is when the amount of water lost through transpiration exceeds the amount absorbed through the roots.
  • Individual cells lose turgor and become plasmolysed and the leaves and stems droop.
  • The condition is corrected at night when absorption of water by the roots continue while transpiration is absent.
  • Eventually, wilting plants may die if the soil water is not increased through rainfall or watering.


Water Relations in Plants and Animals


  • Haemolysis is the bursting of cell membrane of red blood cells releasing their haemoglobin.
  • It occurs when red blood cells are placed in distilled water or hypotonic solution.
  • This is because the cell membrane does not resist further entry of water by osmosis after maximum water intake.


  • Takes place when red blood cells are placed in hypertonic solution.
  • They lose water by osmosis, shrink and their shape gets distorted.
  • Animal cells have mechanisms that regulate their salt water balance (osmoregulation) to prevent above processes that lead to death of cells.
  • An Amoeba placed in distilled water, i.e. hypotonic solution, removes excess water using a contractile vacuole.
  • The rate of formation of contractile vacuoles increases.


Active Transport

  • Active transport is the movement of solutes such as .glucose, amino acids and mineral ions;
  • From an area of their low concentration to an area of high concentration.
  • It is movement against a concentration gradient and therefore energy is required.
  • As such it only takes place in living organisms.
  • The energy needed comes from respiration.
  • Certain proteins in the cell surface membrane responsible for this movement are referred to as carrier proteins or channel proteins.
  • The shape of each type of carrier protein is specific to the type of substances conveyed through it.
  • It has been shown that the substance fits into a particular slot on the protein molecule,
  • As the protein changes from one form of shape to another the substance is moved across and energy is expended.

 Factors Affecting Active Transport

Availability of oxygen

  • Energy needed for active transport is provided through respiration.
  • An increase in the amount of oxygen results in a higher rate of respiration.
  • If a cell is deprived of oxygen active transport stops .


  • Optimum temperature is required for respiration, hence for active transport.
  • Very high temperatures denature respiratory enzymes.
  • Very low temperatures inactivate enzymes too and active transport stops.

Availability of carbohydrates

  • Carbohydrates are the main substrates for respiration.
  • Increase in amount of carbohydrate results in more energy production during respiration and hence more active transport.
  • Lack of carbohydrates causes active transport to stop.

Metabolic poisons

  • Metabolic poisons e.g. cyanide inhibit respiration and stops active transport due to lack of energy.


Role of Active Transport in Living Organisms

Processes requiring active transport:

  • Absorption of mineral salts from the soil into plant roots.
  • Absorption of end products of digestion e.g. glucose and amino acids from the digestive tract into blood stream.
  • Excretion of metabolic products e.g.urea from the cells.
  • Re-absorption of useful substances and mineral salts back into blood capillaries from the kidney tubules.
  • Sodium-pump mechanism in nerve cells.
  • Re-absorption of useful materials from tissue fluid into the blood stream.


Practical Activities

1.Experiment to Demonstrate Diffusion

  • Various coloured substances such as: dyes, plant extracts and chemicals like potassium pennanganate are used.
  • Potassium manganate (VII) crystals are introduced to the bottom of a beaker filled with water using a glass tubing or drinking straw which is then removed.
  • Observations are made and the disappearance of the crystals and subsequent uniform colouring of water noted.

2.Experiment to Demonstrate Osmosis Using a Visking Thbing

  • A strip of visking tubing 8-10 cm is cut and tied at one end using strong thread.
  • About 2 ml of 25% sucrose solution is put inside and the other end tied with thread.
  • The tubing is washed under running water and then blotted to dry.
  • It is immersed in a beaker containing distilled water and left for at least one hour or overnight.
  • It will then be observed that the visking tubing has greatly increased in size and has become firm.
  • A control experiment can be set up using distilled water inside the visking tubing in place of sucrose solution.

3.Experiment to Show Osmosis using Living Tissue

  • Irish potato tubers are peeled and scooped out to make hollow space at the centre.
  • Sucrose solution is placed inside the hollow, and the potato tuber placed in a beaker or petri-dish with distilled water. A conttrol is set using a boiled potato.
  • Another one using distilled water inside hollow in place of sugar solution.
  • The experiment is left for 3 hours to 24 hours.

4.Experiment to Demonstrate Turgor and Plasmolysis in Onion Epidermal Cells

  • Two strips of onion epidermis are obtained.
  • One is placed on a slide with distilled water while the other is placed on a slide with 25% sucrose solution and a coverslip placed on top of each.
  • The mounted epidermis is observed under low power microscope and then left for 30 minutes.
  • After 30 minutes, observations are made again.

The cells in distilled water have greatly enlarged. Cells in 25% sucrose have shrunk.