Subject : 


Topic :


Term :

Second Term


Week 8

Class :



Previous lesson : 

The pupils have the previous knowledge of


that was taught in the last lesson



Behavioural objectives :

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






  • Explain   The Water Cycle
  • Explain   The Nitrogen Cycle
  • Explain   Decomposition in Nature


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. The Water Cycle
  2. The Nitrogen Cycle
  3. Decomposition in Nature


The Water Cycle

Water circulates primarily throughout the abiotic atmosphere. Only a small proportion recycles through living organisms. Vegetation take up water from the soil in massive quantities. They use just a little a part of it in photosynthesis and different metabolic reactions and lose most of the water to the environment by transpiration. Animals absorb water by way of their food and drink, and lose most of it by way of respiration, urination and defecation. Water can also be launched into the environment by decomposition and combustion.[mediator_tech]

The water cycle is maintained mainly by the evaporation and condensation of water within the abiotic atmosphere. The infinite cycling of water on earth as rain, again to the environment by way of evaporation, then again to the earth once more as rain maintains the varied aquatic environments and the provision of water which is critical for all times on land. The water cycle carries many chemical nutrients through the ecosystem and it is a vital consider modifying environmental temperature.


Summarily, processes involved in the completion of the water cycle include

  1. Evaporation
  2. Transpiration
  3. Respiration
  4. Condensation
  5. Precipitation
  6. Infiltration

The Water Cycle


PRECIPITATION: Water that falls to the earth is called precipitation. Precipitation consists of rain, snow, and other forms of moisture.


STORAGE: Precipitation is stored on Earth as snow and ice in streams, rivers, lakes and oceans. Some precipitation sinks into the ground and is called groundwater.


RUNOFF: Water that flows from land into streams, rivers, lakes and oceans is called runoff. Groundwater also runs off from areas that have more water to areas with less water.


EVAPORATION AND TRANSPIRATION: Water in oceans and on land is absorbed into the environment by a course of known as evaporation. When water evaporates, it adjustments from a liquid right into a gasoline known as water vapour. Many of the water that enters the environment evaporates from the floor of the oceans.


CONDENSATION: In condensation, water vapour in the atmosphere changes into tiny ice crystals or water droplets when the air gets cold enough. These ice crystals or water droplets form clouds. When the ice crystals or water droplets in a cloud get heavy enough, they fall to Earth as precipitation.

The Importance of Water to Living Organisms

  1. Water constitutes about 90% of the protoplasm.
  2. It is important in the circulation of blood, food, hormones and enzymes in the body.
  3. It is necessary for the digestion of food.
  4. It facilitates the absorption of digested food.
  5. It is necessary for the excretion of wastes materials like urea.
  6. Metabolic chemical reactions for building up complex compounds in living cells take place in the presence of water.
  7. Mineral salts are absorbed from the soil in solution.
  8. Water is required for photosynthesis to take place.
  9. Mineral salts and organic substances are carried to and from the leaves in solution.
  10. Water provides herbaceous land plants and aquatic plants with mechanical support.



  1. Describe the water cycle.
  2. Of what importance is the water cycle to living organisms?
  3. Make a simple diagram of the water cycle.


The Nitrogen Cycle

This involves the series of processes by which nitrogen is circulated between the biotic and abiotic components of the ecosystem. In the biotic component, nitrogen is found incorporated in amino acids and proteins. In the abiotic component, it is found in the atmosphere as gaseous nitrogen and as inorganic salts (e.g. nitrates) in the soil.

Nitrogen is fixed into the soil by;

  1. The activities of soil bacteria such as Azotobacter and Clostrdium which fix atmospheric nitrogen into the soil.
  2. Activities of nitrogen fixing bacteria living in the root nodules of leguminous plants e.g. Rhizobium.
  3. Thunderstorms.
  4. Putrefaction (decomposition) of dead plants and animals and the excretory products of animals.

Nitrogen is removed from the soil by;

  1. Absorption by the roots of plants.
  2. Denitrification by bacteria.
  3. Leaching.

Intensive cultivation of soil over the years has depleted the nitrogen content of soil. To improve soil fertility, farmers now replenish soil-nitrogen content by the addition of inorganic fertilizers and organic manure.

The Nitrogen Cycle

Importance of Nitrogen to Plants and Animals

  1. Plants absorb nitrogen from the soil as nitrates or ammonium salts and use it to make proteins and other nitrogen containing compounds needed for proper growth and development.
  2. Animals obtain their nitrogen in form of proteins in plants and use it to build new cells and repair worn out tissue.
  3. Some soil bacteria obtain energy by oxidizing ammonium salts and nitrates.[mediator_tech]
  4. Symbiotic bacteria in the root nodules of leguminous plants synthesize organic substances (protein) from atmospheric nitrogen.




Decomposition in Nature

Decomposers are organisms which feed on dead and decaying organisms and on their excreta (urine and faeces). They bring about the decay of these materials. Decomposers are saprophytes and can be grouped into two classes;

  1. Micro-decomposers: these are microscopic bacteria and fungi.
  2. Macro-decomposers: these include mushrooms, toadstools and mould. Others are detritus-eating animals such as earthworms, termites, millipedes, wood lice, lobsters and clams.

Decomposers secrete enzymes onto their food source. These enzymes break down complex organic compounds like carbohydrates and proteins into simple, soluble, inorganic compounds and also release a lot of heat in the process. The decomposers use only a small portion of the nutrients and energy for their metabolic activities. The remaining nutrients are released into the soil, air and water. The heat energy released is lost into the atmosphere. When decomposers die, other decomposers feed on them.

Products of decomposition include gases like carbondioxide, ammonia, hydrogen sulphide and water vapour, and salts like nitrates, sulphates, and phosphorus and potassium ions. Green plants absorb the nutrients released into the soil and air through their roots and leaves and use them to manufacture energy rich food used in supporting consumers in the ecosystem.

Sulfur Fungus

A member of the phylum Basidiomycetes, the sulfur fungus is one of the largest of the edible fungi, reaching a width of several meters and a weight of several kilograms. It typically grows on trees, sometimes at heights that make harvesting these fungi difficult.

The Role of Decomposers

  1. They enrich the soil with nutrients required for plant growth.
  2. They make the recycling of nutrients possible thus enabling the ecosystem to function.
  3. They are used in industries for production of cheese and yoghourt.
  4. Production of linen threads.
  5. Production of compost.
  6. Used for sewage disposal.
  7. Used in the process of fanning.
  8. They produce carbon dioxide used in photosynthesis.
  9. They prevent unsightly accumulation of remains of living organisms on the surface of the earth.
  10. They contribute to environmental pollution.









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




  1. What is decomposition?
  2. Define the term ‘decomposers.
  3. Outline the process of decomposition in nature.
  4. Mention five roles of decomposers.



  1. State three ways by which nitrogen is (i) added to soil (ii) removed from soil
  2. Enumerate two importance of nitrogen to living things.





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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