Biology Lesson Note SS1 Third Term



Week 1            –           Micro-organism around us

Week 2            –           Concept of culturing

Week 3            –           Micro-organism in Action

Week 4            –           Sexual Transmitted infection (STIs)

Week 5            –           Towards a Better Health

Week 6            –           Population

Week 7            –           Function Ecosystem

Week 8            –           Energy Transformation in Nigeria



Micro-organism or microbes are tiny organisms which are invisible to the naked eye but can be seen with the acid of microscope.

Micro-organisms are found everywhere e.g. air, water, soil on our bodies and inside our bodies. For instance under the fingernails, mouth cavity, inside ears, nose on the skin, decomposed organic matter and food.

Groups of Micro-Organisms

Micro-organisms are grouped as follows:

  1. Viruses
  2. Bacteria
  3. Protozoa
  4. Some fungi
  5. Some alagae


Viruses are non-cellular organisms without nucleus, cytoplasm and cell membrane.

Structurally, a bacterial virus also called Bacteriophage is made up of a protein coat abd DNA (ideovyribonudeic acid). The protein coat is divided into head and fail region is made up of a trail core protected by a fail sheath. The fail reagion ends with six tail fibres. Some other viruses have RNA (ribonucleic acid) instead of DNA while some have both RNA and DNA. The six tail fibres arise from a tail plate.


Bacteria are unicellular organisms of microscopic size, the largest being about 12 microns (1 micro = 0.001millmeter) long and about 1.5 micro in width.

Bacteria can be seen with high microscope. The first man to discover bacteria was van leeuwenhoek in 1683.

Structure of Bacteria

A bacterial cell consists of a mass of protoplasm surrounded by a wall. The cell wall is covered outside with a slimy layer or capsule which helps to protect the bacterial cell from dehydration and also help to stick to the surface of its host or food.

Cytoplasm: The cytoplasm is bounded inside by plasma membrane and outside by the cell wall. The cell membrane forms the mesosomes which contain various enzymes. The cytoplasm is a dense fluid which contains granules and ribessimes.

Nucleoid: Bacteria have no well-organized nucleus. They have nuclear material without a nuclear membrane. The DNA is concentrated in an area called nucleoid which is not some bacterial cells have flagella which some have food granules.

Different Shapes of Bacteria

Bacteria have different forms

  1. Cocci (Coccus) – the cells are spherical or rounded in shape.
  2. Bacilli (Bacillus) – the cells are rod-shape. Some of them bacilli have flagella.
  3. Spirilla (Spirillus) – the cells are spirally twisted. Some have flagella – Treponema
  4. Vibrio – the cells are comma-shaped e.g. vibrio cholera


Protozoa are microscopic and unicellular animals found in both marine and fresh water and damp soil. Some are frace-living e.g. Amoeba, Paramecium while others are parasitic e.g. Plasmodium, Entamoeba histolytica and Trypanosmes.


Fungi are non-green simple plants. They are mostly parasitic or saprophytic in nutrition. Reproduction is mostly by spores. Majority of fungi are micscopic while some are large enough to be seen with naked eye e.g. Mushroom. Examples of fungi are Mucor, penicillium, Streptomyces, aueromyces, tinia and yeast.


Algae are microscopic green plants with the majority mainly found in aquatic environment e.g. Diatoms, Spirogyra, Volvox, Chlamydomonas, Oscillatoria and Nostoc.   




Culturing is defined as a technique of growing micro-organisms in special media in the laboratory. It involves the making of sterile medium, inoculating, incubating and examining of micro-organisms. By this means, micro-organism characteristics such as colour, pattern of growth and appearance can be seen. Culture of micro-organisms can be grown from the water, air, animals, plants and various parts of human body.

Preparation of Culture Solution

  1. The culture solution which agar is prepared under sterile condition
  2. Then boil and pour it into sterile petri-dish
  3. Allow it to cool and set in the petri-dish
  4. A heat sterilizes may be used to kill micro-organisms in the petri-dish
  5. The material is then introduced into the agar medium and covered immediately
  6. Place the petri-dish in a warm but dark compartment or an incubator
  7. Observe and record what you have seen for 2-3days.

Identification of Micro-Organisms

Micro- organisms can be identified in the air, pond water, river and stream by preparing a culture medium.

Five Petri-Dish with Sterile Agar Medium are used.

  • To petri-dish    (1) expose it to air for about 10-15 minutes and then cover it.
  • To petri-dish    (2) drop few pond water and cover it immediately
  • To petri-dish    (3) drop some river water and cover it
  • To petri-dish    (4) drop few stream water and cover it
  • To petri-dish    (5) do not add anything to it apart from the sterile petri-dish to serve as control.

Leave all the petri-dish in the labouratory for 3-4days.

Observe allthe petri-dish for the colories of micr-organism in each dish.

Record the characteristics such as colour, pattern of growth, appearance of the colories of the micr-organisms in each petri-dish.

The recorded observation is then followed by discussion.

Micro-organism in our body and food

Experiment 1

Aim       –          To show that micro-organisms are present in the dirt under the finger nail


Scrape the dirt under the nail with a sterilized knife into a petri-dish. Five drops of distilled water are added into the dirt in the petri-dish and well stirred with sterilized needle. The solution is then speed on the surface of a nutrient agar mixture in petri-dish ‘A’ into another petri-dish ‘B’ containing a nutrient agar mixture. Four drops of distilled water are added and spread on the surface and this acts as control experiment. Both petri-dishes A and B are covered and kept in the laboratory room temperature.


After three days, coloured patches are seen in the surface of petri-dish ‘A’ when the coloured patches are viewed under a microscope, bacteria of round and rod-shape types are seen. Fungi such as mucor and rhizopus are also seen. No coloured patches are observed in the petri-dish ‘B’

Conclusion     –           Micro-organisms are present in dirt under the finger nail.

Experiment 2

Aim     –           To show that micro-organisms are present in the mouth cavity


A clean and sterilized cotton swab is used to rub the tooth at the region of the neck or tongue or the cheek- transfer the scrapings into a sterilized test tube containing five drops of distilled water. Us a sterilized dropper to turn the debris in the distilled water and transferred a drop into a clean plain microscope in the low and high power magnification.


The micro-organism that are likely to be seen are Entamoeba gingivalis and rod-shape bacteria (Bacillus)

Conclusion     -micro-organisms are present in the mouth.

Experiment 3

Aim     –           To show that micro-organisms are present in the air


Get a prepared agar mixture and sterilized petri-dish. Pour the agar medium into the Petri-dish and allow to solidify and cool. Open the agar mixture petri-dish and exposed it to air for 30minutes. The dish is then covered and placed in the laboratory at the room temperature and leave for four days. Another petri-dish containing an agar mixture and not open to air is also kept for four days to serve as control.


Opening the petri-dish kept in the laboratory of room temperature, coloured patches are seen. On examination under the microscope, the coloured patches contain bacteria and fungi (yeast and mucor ) no patches will be seen on the petri-dish not expose to air.

Conclusion     –           Micro-organism are present in the air.        

Experiment 4

Aim     –           To show that micro-organism are present in our food


Three petri-dishes A, B, C containing nutrient agar are used. Into petri-dish A, place some tiny pieces of cooked yam or other food which has been cooled and exposed to air for 5minutes and cover them again quickly. Into petri-dish B , place tiny pieces of cooked meat which have been cooled and exposed to air for 5minutes and cover quickly. Petri-dish C, is left intact, that is not open to air and contain no food material. The petri-dishes are then kept in a warm place in the laboratory for 2-3days. A sterilized needle is used after 3days to take samples from each petri-dish and spread on microscope slides. Smears are prepared and stained. The slides are view under the high power magnification of the microscope.


The petri-dish A and B into which food materials are added will show growth of micro-organisms such as bacteria and fungi while petri-dish C remain clear of any patches of growth of micro-organism.

Conclusion      –           Micro-organism are present in exposed food.


Carriers are agents which are capable of transferring or carrying micro-organisms from one place to another. Non-living agents that carry micro-organism from place to place are air, water and food.

Vectors are animals which transfer the living agents called pathogens from aone place to another. The carriers’ use various parts of their bodies e.g. legs, wings, mouth part, hairy bodies etc. to carry micro-organism.

Therefore, micro-organisms can be located in the mouth, legs, abdomen, wings and hairy bodies of the insect.

Vectors or carrierMicro-organismDisease caused
Anopheles mosquito (female)PlasmodiumMalaria fever
Tsetse flyTrypanosomeSleeping sickness
House flyVibrio choleraCholera and typhoid fever
Rat flea/body louseRickettsiaTyphus
Aedes mosquitoVirusYellow fever and dengue fever
Rat fleasBacteriaPlague




Micr-organism show growth by increasing in size, mass or number of cells. When the environmental conditions for growth such as food, adequate temperature and humidity will hasten their growth.

Ways of measuring growth of micro-organism

By inoculating a bacteria cell into a clear nutrientbroth. As the bacteria population increases, the clear liquid medium becomes cloudy or turbid.


Beneficial Effects

  1. Bacteria are used in compost formation by causing decay.
  2. Some bacterial have ability to fix nitrogen in the root of modules of leguminousplant.
  3. Maintenance of soil fertility whendecomposed releasenutrient to the soil.
  4. Digestion of cellulose
  5. It aids decomposition of dead plant and animal
  6. Bacteria are used in sewage treatment.


  • Manufacturing of drugs and vaccines
  • Yeast and certain bacteria are sources of vitamin B complex
  • Bacterial and yeast are good source of enzymes such as amylase and invertase
  • For baking
  • Preparation of alcoholic drinks
  • Making of cheese/yohurt
  • Tanning of hides and skin
  • Curing of tobacco

Harmful Effects of Some Bacteria

  1. Causes of diseases
  2. Spillage of food
  3. Deterioration of matrials
  4. Causes of death.



1.         Poliomyelitis is a serious characterized by fever and meningeal symptoms and by paralysis of the body. It is caused by a virus called poliovirus.

Mode of transmission is by drinking an infected water or eating infected food or by breathing infected air.


Fever, headache, vomiting and general discomfort, backache, stiffness of the neck, paralysis of muscle, difficulty in swallowing and breathing.


  • Mavs vaccination
  • Good sanitation by both individual and public health workers.
  • Do not swim in dirty water
  • Keep away form getting chilled as this may lower body resistance against poliomyelitis.
  • Watch for early signs of the diseases.

2.   Chicken–pox is an infections viral disease characterized by spots with blister, fever, headache and it is caused by virus.

Mode of infection – It is airborne

Symptoms – high temperature headache, fever and spots (rash) with blister.

Control     – Isolation of patient

– Disinfection of the room and belongings.

3.  Infective hepatitis (jaundice) It is a disease caused by virus

Mode of infection: By breathing in infected air with the virus or by drinking infected water and milk or food.

Symptoms: headache, high fever, vomiting, abdominal pain, jaundice. Liver enlarges, presence of bile in urine, loss of appetite.


  • Isolation of patient
  • Disinfection of stool
  • Strict sanitation is very important

Measles  This is a serious disease in young children caused by virus.

Mode of infection- by breathing infected air or by close contact with infected person.

Symptoms: catarrh, sneezing, fever, cough, rash can the face of first and spread all the body later.


Animal diseases caused by bacteria include tuberculosis, leprosy, tetanus, typhoid, dysentery syphilis, gonorrhea.

A.         Gonorrhea is a veneral disease caused by bacteria called Neisseria Gonorrhea.

Mode of infection – Usually by sexual intercourse with an infected person of the opposite sex. New born babies occasionally become Infected during birth if the mother is infected.

Symptoms: After 3 to 7 days of infection, there is a creamy discharge of pus from the penis. Burning pain when passing urine. Frequent passing of urine.


  • Commercialized prostitution should stop
  • Infected person should report early for medical treatment.
  • Infected person should stop having sex with previous partners until he or she receive treatment
  • Sex education is necessary to enlighten the youth.

B.         Syphilis is also a venereal disease caused by bacterium called Treponema palladium.

Mode of infection: it is by sexual intercourse with an infected person through a break in the skin.

Symptoms: Sores on penis, vagina, labia, mouth and rectum.

Second stage symptoms:       ever, headache, sore throat, loss of appetite and skin rash.

Third stage symptoms:          Insanity, paralysis, blindness, deformity of bones and deafness.

Control: The same way for gonorrhea

C.         Cholera this is a disease caused by a bacterium called Vibrid cholera.

Mode of infection : –

  • By drinking water or milk infected with the organism .
  • By eating food and vegetable with the organism
  • By houseflies that land on yhe vomit of the infected person.

Symptoms: Serves watery diarrhea and vomiting

  • Abdominal pain, dehydrating as result of loss of body fluid, unconsciousness and death may occur.


  • Immediate report of any suspect to the nearest hospital.
  • Complete isolation of patient.
  • Water must be boiled before use.
  • Public water must be purified
  • Enforced strict observation of law of hygiene
  • Food stuffs must be protected from flies
  • Hand must be washed with disinfectants
  • Mass vaccination with cholera inoculation
  • Strict observation of immigration rules for aliens
  • Treatment of infected person.

D.         Tuberculosis this is a disease caused by a bacterium called Mycobaterium tubaculosis.

Mode of infection:

  • By breathing in an infected air or dust.
  • Drinking infected water or eating an infected food such as meat or milk of infected cow.
  • Personal contact with an infected person
  • Flies can also carry the germ to our food.


Severe cough with blood in sputum, loss of appetite, indigestion and loss of weight, high temperature and sweating at night.


  • Strict sanitation
  • Eating nourishing food to increase body resistance.
  • Living in well ventilated house
  • Isolation of patient
  • People are to be protected by vaccination
  • Treatment
  • Careful disposal of human feaces
  • Boiling of drinking water is necessary
  • Hand, vegetable and fruits must be thoroughly washed
  • Infected person should be treated.


Are non-green simple plant. They are mostly parasitic or saprophytic in nutrition. Examples of fungi are mucor, penicillium, Streptomyces and yeast. Some diseases caused by fungi are ringworm, foot athlete’s etc.

Ringworm: it is a fungal disease caused by a fungus called Tine

Mode of infection: contact with an effected person or belonging of the suffer.


Circular red patch on the part of the skin infected. Ringworm of the hairs cause hair to fall off.


  • Good personal hygiene
  • Avoid wearing wet shoes and cloths
  • Avoid contact with infected person
  • Spray infected materials with fungicides
  • Consult a doctor

PROTOZOA DISEASES are microscopic and unicellular animals found in both marine and fresh water and damp soil. Some are free-living e.g. Amoeba, Plasmodium while others are parasitic e.g. Plasmodium, Entamoeba and Trypanosome.

1.         Malaria is a disease caused by Plasmodium which is transmitted by the bite of a female anopheles mosquito.

Symptoms – Chill, High Fever, Sweating at times vomiting.


  • All breeding places are to be eliminated.
  • Pouring of kerosene or oil on the surface of the larva
  • Introduction of fish such as tilapia to feed on the larvae.
  • Use of mosquito net.
  • Use of insecticide to kill the vector of the disease which is adult mosquito
  • Usage of preventive drugs by man
  • Using of mosquito repellants.

2.         River blindness iss a disease caused by micro-filarial worm. Onchocerca is transmitted by an infected blood sucking blackfly called similium (vector)


  • Complete abundance of bite of blackflies
  • Use of repellant to rub body
  • Prompt treatment of infected person is necessary
  • Sleeping sickness is caused by Trypanosome whose vector is tsetse flies.

3.         Sleeping sickness is caused by Trypanosome whose vector is tse-tse flies.

Mode of transmission is by bite of infected tsetse fly.

Symptoms:  fever, headache, weakness, swelling of lymph glands, oedema and anaemia.


  • Clearing of vegetation around the banks of lakes and river.
  • Spray the bushes with insecticides to kill the fly.


Bilharziasis (schistosomiasis) blood fluke of man.

This disease is caused by a blood fluke called Bilharzia or schistosoms.


Skin irritation of the point of entry after  few   hours. Fever, headache, sweating and backache. Blood is found in the urine or faeces. It causes enlargement of liver and spleen causing anaemia.


  • Faeces and urine should not be passed to water.
  • Infected water can be treated with copper sulphate or lime to kill the snails host.
  • Clearing of the standing vegetation in the water.
  • Clear the body immediately after bathing.




Sexually transmitted infected diseases are infections that can be contracted through having sex with an infected person.

Mode of transmitting is having sex with an infected man or woman. Examples are gonorrhea, syphilis, urethritis herpes, Chlamydia, HIV.

Acquired Immune Deficiency Syndrome (AIDS): This is caused by immune-deficoency virus (HIV).

Mode of transmission

  • By sexual intercourse
  • By anal sex as practiced by homosexuals
  • By transfusion of blood of infected person
  • By oral sex
  • By using unsterilized infected needles
  • From infected mother to her baby in the womb during pregnancy.


  • Weight loss greater than 10%
  • Fever longer than one month
  • Chronic diarrhea longer than one month
  • Persistent severe fatique
  • Persistent cough longer than one month
  • General skin irritation
  • Swelling of the glands
  • Control
  • National mass campaigns to educate everyone of the danger of HIV
  • Keep to one faithful partner
  • Use of condom when having sexual intercourse
  • Blood must be screened for AID virus before marriage
  • Avoid anal and oral sex
  • Avoid kissing
  • Infected person should avoid pregnancy as the baby may be infected
  • Foreigners who are to stay in a country should be certified HIV free.


i.          Describe briefly an evidence of index of growth of micro-organisms.

ii.         Explain the ways of measuring the growth of micro-organism.

iii.        List four disease which are transmitted through food and water

iv.        Briefly explain the beneficial effects of micro-organisms in: a. Nature b. Industries

v.         What are Sexually Transmitted Diseases?

vi.        Name and describe three transmitted diseases.

vii.       List five groups of micro organisms

viii.      Explain five economic importance of microorganisms.



Control of harmful micro-organisms:

  1. By boiling or heating water and food kill the germs and their spores.
  2. Sterilization of medical instrument and dresses by boiling
  3. Freezing items in freezer will reduce keep the activities of bacteria of minimum
  4. Covering of food
  5. Useage of antibiotics to kill the germ.
  6. Use of antiseptic which may destroy or prevent the multiplication of micro-organisms.
  7. Salting prevents food items such as meat and fish which makes the cell of the bacteria to be plasmolysis.
  8. By dehydration that is removing the water from food items e.g. fish, meat and other food items.
  9. Good sanitation is essential good health by keeping the body clean.
  10. Clearing the bushes to destroy the habitat of the vectors of diseases.
  11. Isolation of infected person
  12. Eating of balanced diet.


A vector is an animal that carries pathogenic organism. Most vectors are arthropods especially insect e.g. housefly, mosquito, plasmodium.

Ways of Controlling Vectors


  1. Draining of swamp
  2. Clearing of bushes around houses
  3. Sleeping in room protected by mosquito
  4. Spray swamp/room with insecticides
  5. Spray oil on stagnant water to kill the larvae
  6. Burying of broken pots and empty cans
  7. Using insect repellant on the body
  8. Use of biological control i.e. introduction of predator.
  9. Use of drugs.

Control of Houseflies

  • Spraying of insecticides
  • Destruction of breeding materials/places
  • Keeping environment clean
  • Use of poison baits
  • Closing of pit toilet
  • Covering of food

Control of Blackflies

  • Clearing of bushes around houses
  • Fumigation with insecticides
  • Distraction of breeding spots
  • Proper monitoring of water bodies
  • Use of drug

Maintenance of Good Health

1.         Proper refuse disposal: Refuses are solid waste materials or dry or wet solid waste collected from markets, home, hospital, offices and factories. E.g. waste paper, food, cans, cobs of maize, yam and cassava peels.

Ways of disposing refuse

  • Provision of dust bin or waste bins in strategic location.
  • Burning refuse in incinerators
  • Dumping them in isolated areas far from human habitation
  • Burning refuse in a sanitary land fill.

2.         Proper sewage disposal: Sewage is waste water materials or wet waste resulting from the following:

  • Faeces and urine (toilet )
  • Bath water
  • Waste water from houses and street
  • Waste from factories
  • Agricultural waste
  • Waste from kitchen

Sewage contains 99% water while the remaining 1% contains impurities and micro-organisms.

Ways of disposing sewage

  • Use of pit toilet where urine and faeces are passed into the pit
  • Use of septic tank where water is used to flush faeces and urine into a big tank dug in the ground
  • Community treatment process where sewage from various homes are collected and treated before being discharged into ocean or rivers.

3.         Protection of water: The water we drink and bathe with must be protected from diseases. Sources of water include well, rivers, streams, lake, reservoirs and rainfall.

Ways of protecting water

  • Addition of alum to water
  • Boiling of water before drinking it
  • Filtration of water on cooling
  • Addition of chlorine to kill microscopic germs
  • Storage of water in clean container.

4.         Protection of food: Food is important and it gives good health. It must be protected from germ all the time.

Method of Protecting Food

  • By keeping food in refrigerator or deep freezer
  • Boil or cook raw food properly before eating
  • Inspection of food meant for public consumption
  • Washing of hands before and after eating
  • Food can be preserved by canning
  • Keep the environment where food is clean
  • Avoid exposure of food to flies and other micro-organism

Control of diseases includes:

  • Living in clean environment
  • Sweeping of surroundings
  • Take bath regularly
  • Wearing clean and neat cloth
  • Living in a well-ventilated houses
  • Prompt treatment of infection and injury
  • Cleaning of latrine  and urinals with disinfectants regularly.


Different organization have been established to maintain good public health both at the National and International levels. Some of these organizations are Red Cross, United Nation International Children Emergency Fund (UNICEF), World Health Organization ( WHO ) , Food and Agricultural Organization (F.A.O) , Public Health Authority and Medical Association.

A.         World Health Organization (WHO)

This is a specialized division of the United Nation Organization (UNO) established in 1948 with the headquarter in Geneva, Switzerland.


  • It promotes measure for the control of diseases through vaccination programmes and use of antibiotics.
  • It coordinates research programmes in all fields of health and make the result know to all member nations
  • It assists in sending medical personnel to countries on request to advice on the best method of improving their health service.
  • It promoter nutritional and sanitary products
  • It assist in the training of medical personnel
  • It reports outbreaks of infectious diseases in one country to other.
  • It helps in standardizing the quality and dosages of drugs.
  • It prepares international Health statistics
  • It helps to stop spread of infectious diseases
  • It publishes literatures  on health which are circulated all over the world
  • It assists in finding solution to mental problem.
  • It controls the distribution of dangerous drugs.
  • It assists in pre-natal and post-natal  care.
  • It organizes immunization for children as prescribed by doctors

B.         United Children’s Educational Fund (UNICEF)

This organization was set up to improve the health and welfare of the children all over the world. Specific functions include:

  • To provide for emergency needs of children in devastated areas
  • To improve the nutrition of under nourished children.
  • To feed the destitute children
  • To supply vaccines or equipment’s to prevents or control diseases that specifically affects children.
  • To provide children’s clothing and other needs
  • To assist in the improvement of the mother and their children by providing training.

C.         Red Cross

Red Cross society is world-wide organization concern with alleviating human        suffering and misery in time of war and disaster such as earthquake s, flood and drought. It has its headquarter in Geneva.

Functions /Roles

  • It gives aid to ex-servicemen
  • In time of war, the organization provides food, medicines, cloths for wounded people .
  • It campaigns for blood donation for those in need of blood.
  • It prepares first aid books for people.
  • It evacuates people especially  during the war from unsafe zones.
  • It provides relief work such as  food, medicine, clothing in time of disaster .
  • It renders first aid during sports meeting.
  • It helps to provide information for missing persons
  • It pays visit to prisoners of war and present them with gift.

D.         Nigeria Medical Association (NMA)

This is a national body concerned with the maintenance of good health within Nigeria.


  • Advising the government on how to improve the health status of the people.
  • Alerting the nation when there is an outbreak of a diseases.
  • Carrying out research into ways of preventing and controlling diseases
  • Monitoring the recruitment of well trained doctors in hospitals.
  • Assisting in the training of medical and paramedical staff needed in health care delivery.


1.         List seven (7) ways by micro-organisms can be controlled to maintain good health. (SSCE Nov. 1990).

2.         (a) Define a vector

(b) Name five diseases transmitted by vector

3.         State six methods by which mosquito can be controlled and state reason for each method (SSCE June 1993)

4.         Discuss how the following can be protected against diseases infestation:

i. Water           ii. Food.

5          State five functions each of the following health organization:



Red Cross



Population is defined as the total number of organism of the same species living together in a given area at a particular time.

Population size is defined as the total number of the species of the same species living in a given area or habitat.

Population density is defined as the number of individual organisms per unit area or volume of the habitat. It is represented mathematically as:

Population density      =          Total population/ population size

                                                             Area of habitat

Population size            =          population density x Area of habitat

Population frequency – This is defined as the number of times organism occurs within a given area of an habitat.

Population dominance

Method of Population Studies

  1. Direct counting
  2. Tagging ( capture, release and recaptured )
  3. Quadrat sampling
  4. Use of transect.

1.   Direct counting: This involves counting a particular species of organisms in a particular area. The complete counting of individual in an area is called censor.

2.   Tagging or (captured, release and recaptured) method: this is a method of capturing a known number of a particular species of animal  in a particular area. The captured animals are tagged or marked then released. After a known period, the same number of those animals are captured again from that area. Suppose 200 rats are captured in an area and the 200 rats are then tagged or marked and released. After two days another 200 rats are captured. If the 200 rats captured after 2days, include 40 tagged ones, the total population of tagged and untagged rat in the area is 1000.

T.P             =          200/40  x  200 5

                         =          1000 rats

3.         Quadrat sampling method: A quadrat is a ecological instrument to estimate population. It may be square, circular or rectangular.

How to Conduct Population Studies with Quadrat

  • Choose and locate the sample plot area.
  • Identify the species of organism in the plot
  • Measure the area with a measuring tape to know the area of the habitat. ( mapping out of the sample plot )
  • Throw or loss the quadrat randomly at an interval for up to ten (10 ) times or above.
  • After each throw, count the number of species with the area of quadrat.
  • Record the number of organism in each throw.
  • The population density of the species  can be calculated by dividing the average number of times a species  occur with the quadrat by the area of the quadrat.
Number of goat weeds per area of quadrat  15  10  12  20  6  18  19  26  8  13  127
  Number of earthworms per area of quadrat  2  4  1  4  3  7  5  2  6  11  35

Area of abandoned farm        =          100m2

Area of quadrat                       =          1m2

No of unit are tossed =          10

Total unit area tossed   10 x 1 =          10m2

No of goat weeds in   10m2    127

Average frequency      no of goat

                                    Weeds per square       =          127

                                    Meter of quadrat                    10

Population density of goat weeds      =          12.7/m2

Population density                              =          population size of a goat weeds

                                                                        Area of quadrat x no of toss

                                                            =          127      =          127

                                                                        1 x 10               10

=          12.7/m2

Population size                        =          population area density *area of quadrat

                                                            =          12.7 x 10

                                                            =          127


This method makes use of a rope or tape marked at regular intervals is stretched across the study plot. Plants or animal occurring at the marked intervals are recorded. If this is done several times in different places, the types of plant and their number can be estimated.

The method has an advantages since transact shows the kinds of plant along a line or belt vegetation, the method can be used to study any progressive change in vegetation by re-charting the transact.

Factors that affect population size

Natality  : this has to do with birth rate in mammals, hatching in oviparous animals and germinate in plant.

Mortality : this is the rate of removal of individual from a population by death.

Immigration : this is the movement of individual organism into a population.

Emigration : this is the movement of organism out of a population or in a particular habitat.

Dispersion : it is the manner in which individual in a population are spread in a particular area.

Growth rate this is the net result of natality, mortality and dispersion.

Simple measurement of ecological factors

Rainfall is an important ecological factor because it affects the distribution and type of vegetation. It can be measured by RAINGUAGE.

Temperature affects the rate of transpiration, photosynthesis, germination and other process. It can be measured by using THRMOMETER.

Light is very important for photosynthesis both in terrestrial and aquatic environment. It can be measured by LIGHT METER OR PHOOMETER.

Relative humidity is the amount of water vapour in the air. It can be measured by using HYGROMETER.

Wind : the speed of wind is measured by an ANEMOMETER. Wind direction is measured by WIND VANE


Turbidity is the amount of suspended particles present in the water. It is measured by SECCHI disc.



Ecosystem is a natural functioning unit in nature it is made up of living organisms and their non-living environment. The biotic component such as producer or consumers interacts in their environment resulting in ecosystem being a functional unit.

Autotrophs, Heterotroph and decomposer

Autotrophs are organisms (green and some bacteria) which can use sunlight or chemical to manufacture their food from inorganic substances during the process of photosynthesis. Autotrophs are otherwise known as producer.

Producer is a green or autotroph which trap the energy of sunlight or solar and convert to form organic compound.

Terrestrial examples of autotrophs are grasses, trees and shrub while aquatic autotrophs are phyk- plankton, water hyacinths, and sea weeds.

Heterotrophs are organism mainly animals, which cannot manufacture their own food but depend directly or indirectly on plant for their food, hence, they are called consumers. Consumer can be grouped into the following:

Herbivores or primary consumer are the animal that feed directly on the plant.

Carnivores or secondary consumers are the animals that feed on primary consumers e.g. flesh eater organisms. Lion, cat, hyenas and leopard.

Omnivores or tertiary consumers are those animals or organisms that feed on both primary and secondary consumers,

Detritivores are those organism or animals that feed on recently dead organisms e.g. vulture.

Decomposer: decomposers are the fungi or bacteria which live saprophytically or feed on dead remains of plant, animal and organisms leading to or breaking down organic matters to produce soluble nutrient which are absorbed by plant. Other examples of decomposer are insect such as termite, larvae of housefly    (maggot) etc.

                                                     Food chain

Food chain is defined as a feeding relationship involving the transfer of energy through food from producer to consumers. This is a linear feeding relationship in which energy is transferred from producer (plant) through a series of organism.

Terrestrial habitat

Guinea grass –   grasshopper       –       toad        –             snake                                –    hawk

(Producer)         (Pry consumer)      (Secondary        (tertiary consumer)


Aquatic habitat

Diatoms –                    mosquito larvae –           tilapia fish                  –                           whales        

(Producer)                    (Pry consumer)               (Secondary consumer)                     (Tertiary consumer)

Terrestrial food chain

Humus             –           earthworm      –           domestic food                         –           man

Food web is defined as a complex feeding relationship among organism in the same environment with two or more inter-related food chain.

Food web contain two or more food chains and therefore more organism than food chain

                                                           Solar producer



                                        Cane rat           grasshopper          Mouse     primary consumer


 Snake    secondary consumer

                                            Fox                   Hawk                       Eagle           tertiary consumer


Tropical level

Tropical level is defined as the feeding or each stage in a food chain or food web. OR Tropical level is the number of links by which food energy is transferred from producer to final consumer.


Guinea grass –            grasshopper             –     toad                –             lizard     –           hawk

(1st tropical level)    (2nd tropic level)            (3rd tropical level)      (4th tropical level)     (5th tropical level)

Pyramid of number

Pyramid of number is referred to the number of individual organisms of each tropic level which decreates progressively from the first to the last tropic level in a food chain. Pyramid is a diagrammatic representation of food chain in which producers form the base and the carnivores from the apex.





                                                Guinea grass

Pyramid of energy

Pyramid of energy is defined as the amount of energy present in the living organism at different tropical levels of a food chain.

The pyramid of number represents a progressive decrease in energy from the first tropical level to the last tropical level in a food chain or web.





Flow of energy

Energy of food is unidirectional. It is either used or stored. Light energy from the sun is absorbed by chlorophyll in green plants and used in photosynthesis to produce carbohydrate. The chemical energy is passed along the food chain to the secondary consumer and then to the tertiary consumer or decompose.

  • Clean the body immediately after bathing.



Energy is the capacity to do work, e.g. running, swimming, jumping, playing, acting, sitting even sleeping.

Energy can exist in many forms such as potential or kinetic, heat, light, electrical or chemical.

Chemical energy is the form in which living organisms usually store energy. Atoms combine to form chemical compounds by losing, accepting or sharing electrons. Chemical bonds are formed between atoms. A chemical bond contains stored energy which is called energy bond. When a chemical bond is broken in a reaction, energy is released.

Transformation of energy

Energy can be transformed from one form to another. Chemical bound energy in petrol can be transformed into heat and light energy by burning the petrol. Electrical energy is heat by pressing iron. The transformation of enegy is governed by two laws of thermodynamics.

First law of thermodynamic : state that energy can neither be created nor destroyed but can only be converted from one form to another.

Second law of thermodynamics states in any conversion of energy from one form to another, there is always a decrease in the amount of useful energy or in other word, the law states that no transformation of energy from one state to another is ever 100% efficient.

Energy transformation in nature

In nature energy transformation is about by living organisms. Their activities cause energy to flow through the ecosystem. The sun is the ultimate and external of energy for ecosystem on earth.

Energy loss in the ecosystem

The energy from the sun passes through food chain. Only a small portion of the sun’s energy get into the bodies of the final consumer. The rest of the energy is lost as heat in the food chain put a natural limit on the total weight of living matter that can exist at each level.

In autotrophs, the loss in energy affect primary production because there is less in photosynthesis which ultimately affects the yield.

In ecosystem energy is lost through the following:

  1. Vegetation
  2. Soil
  3. Air
  4. Heat
  5. Evaporation of water and
  6. Effects of wind.

Depending on the type of vegetation and climatic factors only about 1-10% of the solar energy may be available to thermodynamic producer in most ecosystems.

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