Environment is defined as the total surrounding or medium of any organism in a given area. This includes the physical surroundings, climatic factors and other living organisms in that surrounding.



The environment, which is the earth, is grouped into four spheres and these are:

  1. Lithosphere: This is the solid portion of the environment which contains rocks, sand, soil mineral, etc.
  2. Hydrosphere: This is the liquid part of the environment like rivers, lakes and oceans.
  3. Atmosphere: This is the gaseous portion of the environment where gases like oxygen, nitrogen, carbon dioxide, etc. are found.
  4. Biosphere: This is the portion of the environment where plants and animals are found.

The four spheres of the environment are interrelated and interdependent on each other.



An ecosystem is defined as the interaction and close relationship between the components of an environment. In other words, ecosystem can also be defined as the relationship between organisms (plants and animals) and its physical environment.

Components of Ecosystem

The ecosystem is made up of two main components. These are:

  1. Abiotic component: This is the non-living component of the ecosystem. It includes factors or elements like soil, water, gases, sunlight, etc.
  2. Biotic component: This is the living component of the ecosystem. It includes plants and animals. However, the biotic component can be grouped into three sub-classes. These are:
  • Autotrophs: These are called These are green plants which can manufacture their own food from simple inorganic substances through the process of photosynthesis.
  • Heterotrophs (primary and secondary consumers): These are organisms which cannot manufacture their own food but depend directly or indirectly on plants for their own food e.g. man, parasites, saprophytes, etc.
  • Decomposers: These are micro-organisms that decompose dead organic matter in order to release nutrients required by producers to prepare their food e.g. fungi and bacteria.

In summary, the components of an ecosystem can also be grouped into the following:

  1. Land (soil).
  2. Water (lake and oceans).
  3. Plants.
  4. Animals.
  5. Drainage (e.g. river).
  6. Climate (Atmosphere).


Interdependence within Ecosystem

The relationship between the components of the ecosystem can best be described as Interdependent. In other words, all the components in an ecosystem depend on one another and they cannot exist in isolation. Again, a state of interdependence within the ecosystem is best achieved where the components are undisturbed.

  1. Interdependence with Abiotic component
  • Rocks weather to form soil.
  • Rocks also change to minerals like coal, petroleum and other soil nutrients.
  • Water from the seas and oceans evaporate to form cloud and rain.
  • Soil formation is influenced by climatic factors like rainfall.
  • Rainfall and temperature are required for chemical weathering of parent rocks.
  • The drainage (rivers, seas and oceans) provides water.


  1. Interdependence within Biotic component
  • Animals depend on plants for their own food.
  • The decomposition of dead animals provides manure for plants.
  • The activities of micro-organisms in the soil also provide growth for plants.
  • Animals during respiration provide carbon dioxide for plants to carry out photosynthesis.
  • Plants also provide oxygen for animals during photosynthesis which they use for respiration.
  • Primary consumers (herbivores) in turn are fed upon by secondary consumers (carnivores).
  • All consumers and autotrophs are in turn broken down by bacteria during decomposition.


  1. Interdependence between the Biotic and Abiotic components
  • The water, carbon dioxide and nitrogen cycles provide energy and nutrients for plant growth.
  • Autotrophs depend on soil for support and nutrients.
  • Autotrophs convert sunlight, energy, water and carbon dioxide during photosynthesis to produce food.
  • All human activities are mainly carried out on the soil.
  • Soil, air and water provide habitat for living organisms.
  • Oxygen and carbon dioxide are made constant through respiration and photosynthesis by living organisms.
  • Food produced from the use of sunlight, water and carbon dioxide are consumed by primary consumers.
  • Primary consumers in turn are fed upon by secondary consumers.
  • Tertiary, secondary, primary and autotrophs are in turn broken down to form soil by bacteria during decomposition.



Environmental balance refers to the ways of recycling matter and the flow of energy within an ecosystem in order to ensure continuous supply or availability.

Environmental balance is achieved through the following processes:

  1. Hydrological cycle (water) cycle.
  2. Carbon cycle.
  3. Mineral nutrient cycle.
  4. Nitrogen cycle.
  5. Food chain and food web.


  • This is the natural exchange or circulation of water between the oceans, the atmosphere and the land.
  • The atmosphere receives water through; evaporation from ocean and rivers from land, transpiration from plants, breathing or respiration by plants and animals.
  • The land receives water through; rainfall from atmosphere, infiltration and percolation.
  • The Ocean receives water through; rainfall from atmosphere, streams and rivers, run-off.

Importance of Water Cycle or Hydrological Cycle and Interdependence

  • Water is an important agent of weathering of rocks.
  • Water helps to dissolve plant nutrients in solutions for easy absorption by plants.
  • Water is also required by plants for photosynthesis.
  • All living organisms require water for normal life processes.
  • Transpiration by plants aids cooling of the plants.


  1. CARBON CYCLE: Carbon cycle involves the series of processes which contribute to the circulation of carbon in nature. Carbon is circulated in form of carbon dioxide.

Loss of Carbon from the Air

  • Carbon dioxide is removed from the air during photosynthesis as green plants use it to manufacture their food.
  • Carbon is also lost in form of carbonates of calcium and magnesium through leaching and drainage.

Gain of Carbon in the Air

The atmosphere gains carbon dioxide through:

  • Burning of fuel like coal, wood and petrol.
  • The action of volcanoes which release carbon dioxide.
  • Through respiration by plants and animals.
  • The dead, decaying and putrefaction of plants and animals.

Importance of Carbon Cycle (Carbon cycle and interdependence)

  • Carbon cycle provides carbon dioxide which is an important gas in the atmosphere.
  • Plants depend on Carbon dioxide for photosynthesis.
  • Carbon dioxide trapped in the leave in the presence of sunlight is used to manufacture food.
  • Animals, therefore, depend on plants either directly or indirectly for their food.
  • Animals take in oxygen and release carbon dioxide to the atmosphere.
  • Plants absorb carbon dioxide and release oxygen during photosynthesis.


  • Nitrogen cycle involves the complex process by which nitrogen is circulated between the atmosphere, soil, plants and animals.
  • Plants can only use nitrogen in form of nitrate.

Soil and Plants gain Nitrogen through:

  • Symbiotic nitrogen fixation through the root nodules of leguminous plants with the aid of some bacteria.
  • Electrical discharge, when oxygen combines with nitrogen in the atmosphere to form nitrate during lightning.
  • Non-symbiotic nitrogen fixation with the aid of some bacteria, nitrogen is fixed aerobically or anaerobically into the soil.
  • Ammonification and Nitrification: Ammonification involves the conversion of dead and decaying organic matter into ammonium compounds while nitrification converts the ammonium compounds first into nitrite and finally into nitrate with the aid of some bacteria.
  • Application of organic manure and nitrogen fertilizers: These add nitrogen into the soil.

Loss of Nitrate from the soil

  • Denitrification: This is the major way by which nitrate in the soil is lost by its conversion to gaseous nitrogen with the aid of some denitrifying bacteria.
  • Other methods include leaching, erosion, soil pH, crop removal, etc.

Importance of Nitrogen Cycle (Nitrogen Cycle and Interdependence)

  • It provides nitrogen which is an important gas in the atmosphere.
  • It provides nitrate which is the main source of protein synthesis in plants.
  • Nitrate is used to produce proteins for animals.
  • It also provides food for micro-organisms in the root nodules of legumes.
  • The bacteria in turn decompose plants and animals to release nutrients when they die.



  • This refers to the circulation of mineral nutrients between plants and the soil.
  • These mineral nutrients include calcium, iron, Sulphur, zinc, sodium, phosphorus, potassium, etc.

Mineral Nutrient Cycle and Interdependence

  • Plants absorb these nutrients from the soil for growth and production.
  • When plants die, they decay and the nutrients are returned to the soil.
  • The decomposition and release of nutrients are aided by micro-organisms in the soil.



Food Chain is defined as the linkage of a series of organisms in a habitat through the flow of energy of consumer levels and their nutritional sequence. In other words, Food Chain involves energy transfer in which each organism feeds on the one before it in a sequence.


Examples of food chain are as follows:

  • Grass → Sheep → Man
  • Grass → Grasshopper → Toad → Snake → Hawk
  • Diatoms → Euglena → Water fleas → Tilapias

The first in each group is usually called autotroph (or producer) e.g. grass, while the next e.g. sheep is called the primary consumer while the last e.g. man is called the secondary consumer.


Trophic Level

Trophic level refers to the feeding stages found in a food chain e.g.

  1. Grass → 2. Grasshopper → 3. Toad → 4. Snake → 5. Hawk

The above food chain has five trophic levels.


Food Web

Food web is a complex feeding relationship of organisms made up of many interrelated food chains. It involves a wider range of energy transfer. The food web contains five different food chains.



Environmental interventions refer to the forces of nature and the activities of man that change the natural existence of the components of the ecosystem.

Types of Environmental Interventions

There are two types of interventions in our environment. These are natural and human interventions.

  1. Natural Interventions: Natural intervention is caused by a number of natural processes which include:
  • Desert encroachment.
  • Sea level changes.
  • Tectonic movement.
  • Volcanism.
  • Earthquakes.
  • Climatic changes.

The Effects of this Natural Intervention include:

  • New features different from those initially they are produced e.g. volcanism creates volcanic mountains.
  • Changes in the landscape of the area e.g. earthquake will result in digging trenches and gullies where it was not initially present.
  • Raising and lowering of beaches.
  • Widespread destruction or extinction of aquatic life e.g. drought results in drying up the water and this will lead to the extinction of water animals.
  • Displacement of animals.
  • Displacement of man.


  1. Human Interventions

Man has interfered with the ecosystem through a number of his activities. This human (man) intervention includes the following:

  • Deforestation.
  • Pollution.
  • Mining.
  • Cloud seeding.
  • Hunting.
  • Urbanization.
  • Land reclamation.
  • Farming activities e.g. burning.
  • Construction.
  • Fishing.
  • Industrialization.
  • Grazing.



  • Deforestation causes increased run-off and flooding.
  • It leads to destruction of natural habitats.
  • It leads to changes in energy balance.
  • It leads to erosion and reduction in rainfall.



  • It leads to less rainfall.
  • It changes the drainage pattern.
  • It reduces the amount of soil moisture content.
  • It leads to loss of some organisms and plants.



  • Atmospheric and water pollution lead to loss of plant and animal life.
  • Oil spillage and water pollution alters the type of plant that can grow in area.
  • Land pollution exposes the soil surface.
  • It leads to changes in the chemical composition of the soil e.g. chemicals used in agricultural practices such as fertilizer.
  • It can also lead to reduction in agricultural land.



  • Overgrazing leads to reduction in agricultural land.
  • It depletes the vegetative cover of the soil.
  • It leads to soil compaction through excessive trampling by animals.
  • It destroys the soil structure and causes soil erosion.



  • It causes the destruction of weeds.
  • It burns the organic matter content of the soil.
  • It causes the destruction of pests and natural habitat.
  • Some may be harmful to man.
  • It can also lead to soil erosion.



  • Mining causes pollution of land.
  • It causes the reduction of farm lands.
  • It leads to pollution of surface and underground water.
  • It also leads to disintegration f settlements.



  • It causes reduction in agricultural land.
  • Wastes produced can cause pollution.
  • It can lead to loss of some organisms and plants.
  • It exposes the soil to erosion and flooding.



  • It destroys the soil structure.
  • It can cause soil erosion.
  • It can also kill plants and animals.
  • Some wastes produced can cause pollution.