Subject : 


Topic :


Term :

Second Term


Week 7

Class :



Previous lesson : 

The pupils have the previous knowledge of

Parts of the Reproductive System of Fish and their Functions

that was taught in the last lesson



Behavioural objectives :

At the end of the lesson, the pupils should be able to


  • Explain  Nutrient Cycling in Nature
  • Describe The Carbon Cycle
  • Explain The Oxygen Cycle
  • Say how The Carbon Oxygen Balance function


Instructional Materials :


  • Poster
  • Wall Chart
  • News paper
  • Online Video
  • Pictures



Methods of Teaching :

  • Class Discussion
  • Group Dialogue
  • Asking Questions
  • Explanation
  • Role Modelling
  • Role Delegation


Reference Materials :

  • Scheme of Work
  • Online Information
  • Textbooks
  • Workbooks
  • 9 Year Basic Education Curriculum
  • Workbooks





  1. Introduction to Nutrient Cycling in Nature
  2. The Carbon Cycle
  3. The Oxygen Cycle
  4. The Carbon Oxygen Balance


Introduction to Nutrient Cycling in Nature

An ecosystem makes use of vitality and inorganic vitamins to operate. Energy is equipped from the sun (an exterior supply) however inorganic nutrients are supplied and re-cycled throughout the ecosystem. The supplies/nutrients that make up dwelling issues are used again and again cycling between the dwelling and non-living environments of the ecosystem..

The major nutrients required to sustain life include carbon, nitrogen, phosphorus, oxygen and water. These are re-cycled through the biological, chemical and geological processes that take place in the environment thus, the nutrient cycles can also be referred to as biogeochemical cycles.

The Carbon Cycle

This is defined as the processes which bring about the circulation of carbon found in the organic molecules of living things.

The Process of Carbon Recycling

Carbon is derived from carbon dioxide in air, dead remains of organisms and in fossil fuels like crude oil and coal.

Through the process of photosynthesis, green plants extract carbon from the atmosphere and incorporate it into their body tissues. The plants in turn are fed on by animals and the carbon compounds get incorporated into the tissues of the animals. When the animal excretes part of the carbon compounds are released into the environment as faeces and urine.

As  plants and animals respire, carbon dioxide is released into the atmosphere. The organic materials in dead plants and animals, faeces, urine, fallen leaves, etc. are decomposed by saprophytic bacteria and fungi. The process of decomposition breaks down complex carbon compounds and releases carbon dioxide which is returned to the atmosphere.

The combustion of fuel like wood, coal and crude oil results in the oxidation of carbon to carbon dioxide which is then released into the atmosphere.

The weathering of rocks results in the release of carbon dioxide which dissolves in water to form carbonic acid (H2CO3). This reacts with limestone to form carbonates and bicarbonates and stored in the sea. The sea helps to control the amount of carbon dioxide in the atmosphere by traping more carbon dioxide when the concentration in air increases. The carbon dioxide is released through the process of diffusion to the atmosphere when the concentration drops.

The actions of volcanoes also release carbon dioxide into the atmosphere.

The Carbon Cycle

The Importance of Carbon Cycle in Nature

  1. Plants use carbon dioxide to manufacture food during the process of photosynthesis.
  2. It provides carbon which is major building block of organic matter.
  3. The carbon compounds in food are the vehicles through which trapped solar energy passes from one organism to another in food chains.
  4. The carbon cycle helps to purify the atmosphere and maintain the atmospheric level of carbon dioxide.
  5. Carbon in carbonates such as calcium carbonate is used by marine animals to build their shells. It is also found in limestone, chalk, marble and coral.



The Oxygen Cycle

Oxygen constitutes about 21% of gases in the atmosphere. This amount is maintained at a fairly constant level by the oxygen cycle.

Through the process of photosynthesis, oxygen is released into the atmosphere. Respiration, decay and combustion are processes which remove oxygen from the atmosphere.

The Significance of Oxygen to Living Organisms

  1. It is used for respiration by plants and animals.
  2. It aids combustion.
  3. It aids decomposition.
  4. It is used in hospitals to aid patients who have impaired breathing.
  5. It is used in airplanes that fly at high altitude

The Carbon Oxygen Balance

There is an approximate balance in the amount of carbon and oxygen in the ecosystem. Human activities such as deforestation and burning of fuels affect the carbon-oxygen cycles. These activities combined with decomposition and respiration, lead to an increase in the amount of carbon dioxide in air and a decrease in the amount of oxygen.

A decrease in the atmospheric oxygen level by 2-8% does not cause any problem but a slight increase in atmospheric carbon dioxide may cause a green house effect. This results in retention of the sun’s radiant (heat) energy which could lead to the melting of the polar ice-caps with a related rise in sea level and flooding. This could also affect important food growing areas of the world.

Human activities have also led to pollution of water bodies resulting in an increase in the activity of decomposers. This has resulted in a significant drop in oxygen level thus threatening the survival of aquatic organisms.

To avert these disastrous penalties, human activities ought to be geared in the direction of sustaining a stability within the carbon-oxygen stage of the environment.






The topic is presented step by step


Step 1:

The class teacher revises the previous topics


Step 2.

He introduces the new topic


Step 3:

The class teacher allows the pupils to give their own examples and he corrects them when the needs arise




The class teacher wraps up or conclude the lesson by giving out short note to summarize the topic that he or she has just taught.

The class teacher also goes round to make sure that the notes are well copied or well written by the pupils.

She or he does the required corrections when and where  the needs come up.







  1. Describe the oxygen cycle.
  2. Listing three significance of oxygen to living things.
  3. What impact will an increase within the quantity of carbon-dioxide within the environment have on living things?


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