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Lesson Note on Biology SS1 Third Term

















SS1 Third Term Biology Lesson Note 

Below are the 2022 complete SS1 Third Term Biology Lesson Note


Week: 1

Topic: Micro-Organisms Around Us


Microorganisms make up a large part of the planet’s living material and play a major role in maintaining the Earth’s ecosystem.

Micro-organisms or microbes are microscopic organisms that exist as unicellular, multicellular, or cell clusters. Micro-organisms are widespread in nature and are beneficial to life, but some can cause serious harm.

Micro-organisms found in Air and Water

Air: The air harbour micro-organisms like fungi (Rhizopus, Yeast, Mucor, Aspergillus and Penicillium spores); bacteria like Mycobacterium spp, micrococci, sarcina and finally viruses like Rhinovirus (which causes the common cold), pox virus, measle virus, etc.

Water: Bacteria like Salmonella, Mycobacteria, Escherichia Proteus, and Pseudomonas are known to live in water. Others are phytoplanktons, blue-green algae, fungi like Aspergillus, Rhizopus, moulds, oscillatoria, spirogyra and ulothrix. The protozoa include Amoeba and Paramecium. To learn more, click here

Week: 2

Topic: Concept Of Culturing 

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

Preparation of Culture Solution

  • The culture solution called Agar is prepared under sterile conditions
  • Then boil and pour it into sterile petri-dish
  • Allow it to cool and set in the petri-dish
  • A heat sterilizer may be used to kill micro-organisms in the petri-dish
  • The material is then introduced into the agar medium and covered immediately. To learn more, click here

Week 3

Topic: Micro-Organisms in Action


Growth of micro-organisms, like all living things, do increase in size and multiply in a number of cells using either the culture medium provided or any suitable surface such as moist bread as a source of food. Microorganisms can also increase in mass. Such an increase in size, mass or number of cells is regarded as growth in micro-organisms.

If environmental conditions of growth such as food, adequate temperature and humidity are favourable, such an increase in mass, size and number of cells of the colony is an index of growth of micro-organisms.

Ways of Measuring Growth in Micro-organisms

There are two major ways of measuring growth in micro-organisms. These are:

First method: A bacterial sample is inoculated into a nutrient agar (a clear liquid culture medium). As the bacterial population increases, the clear liquid medium becomes cloudy and turbid. A progressive increase in turbidity indicates a related increase in the number of bacterial cells. This property is used to measure bacterial growth.

In the laboratory, turbidity can be measured with a spectrophotometer. This instrument measures the amount of light that can pass through a liquid medium. To learn more, click here

Week 4

Topic: Sexually Transmitted Infections (STIs)


Sexually transmitted infections (STIs) are infections that are spread primarily through person-to-person sexual contact. There are more than 30 different sexually transmissible bacteria, viruses and parasites.

The most common conditions they cause are gonorrhoea, chlamydial infection, syphilis, trichomoniasis, chancroid, genital herpes, genital warts, human immunodeficiency virus (HIV) infection and hepatitis B infection.

Several, in particular HIV and syphilis, can also be transmitted from mother to child during pregnancy and childbirth, and through blood products and tissue transfer.

What is a sexually transmitted infection (STI)?

It is an infection passed from person to person through intimate sexual contact. STIs are also called sexually transmitted diseases, or STDs. To learn more, click here

 Week 5

Topic: Towards Better Health


Pathogenic or harmful microorganisms have the ability to wipe out the whole of humanity directly or indirectly. They therefore must be controlled through some measures in order to stay healthy.

Control of Harmful Micro-Organisms

  1. The use of drugs like antibodies performs a key role in checking the spread of microorganisms
  2. Dehydration tends to inactivate the micro-organisms since most of them require water for metabolism
  3. The use of high salinity or salt especially in the preservation of food
  4. Application of high temperature destroys pathogens. This is used in the sterilization of materials e.g. in hospitals
  5. The antiseptic application involves the use of low concentrations of chemicals like phenol (carbonic acid). They prevent or inhibit the growth of microorganisms. At times they kill them
  6. Disinfectants are high concentrations of phenol (carbolic acid). They kill microorganisms outright.
  7. The use of low temperature (freezing) also kills or inactivates some microorganisms. To learn more, click here

Week: 6

TopicPopulation Studies


The population is defined as the total number of organisms of the same species living together in a given area at a particular time. In an ecosystem, the community is made up of many populations of different species.

In population studies of habitat, the following are usually studied:

  • Types of organisms: This involves the listing of the various types of populations that are found in the particular habitat. It helps to determine the relationships that exist between the various organisms (plants and animals) in a habitat.
  • Dominance: Dominance refers to those species that exert a greater influence or a major controlling effect on the other members of the community. The relative importance of a species in the community is expressed by dominance. To learn more, click here

Week 7

TopicFunctioning Ecosystem


An ecosystem is a basic functioning unit in nature. It is made up of living organisms (plants and animals) and their non-living environment. The biotic or living components such as the producers and consumers interact in their environment resulting in the ecosystem being a functional unit.

Autotrophs, Heterotrophs and Decomposers


Autotroph is an organism that serves as a primary producer in a food chain. Autotrophs obtain energy and nutrients by harnessing sunlight through photosynthesis (photoautotrophs) or, more rarely, obtain chemical energy through oxidation (chemoautotrophs) to make organic substances from inorganic ones. Autotrophs do not consume other organisms; they are, however, consumed by heterotrophs. To learn more, click here

Week 8

Topic Energy Transformation In Nature 


The transformations of energy in an ecosystem begin first with the input of energy from the sun. Energy from the sun is captured by the process of photosynthesis. Carbon dioxide is combined with hydrogen (derived from the splitting of water molecules) to produce carbohydrates (CHO). Energy is stored in the high energy bonds of adenosine triphosphate, or ATP.

Energy Loss in the Ecosystem

Solar radiation is used by plants during photosynthesis. Some are lost to the earth’s surface while some are stored in plants’ parts stems, leaves, etc. and are not used up.


First Law of Thermodynamics

The law states that energy can neither be lost nor created especially as it is converted from one form to another. To learn more, click here

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