Decomposers are fungi or bacteria which live saprophytically or feed on dead remains of plants, animals and organisms leading to or resulting in recycling of nutrients by breaking down organic matters to produce soluble nutrients which are absorbed by plants. These are organisms, mainly bacteria and saprophytes responsible for the breaking down of dead organic materials which could be of plants or animals origin. In other words, decomposers cause the remains of plants and animals to decay. These decomposers are grouped into two classes:

  1. Micro-decomposers: These are small or microscopic organisms that can cause decay, e.g. certain bacteria and fungi.
  2. Macro-decomposers: These are bigger organisms that can cause decay of dead organic materials, e.g. earthworms, termites, snails, mushroom and toad stools.


Process of Decomposition

The decomposers secrete enzymes onto their food source such as a decaying plant. These enzymes break down complex organic compounds (food) like carbohydrates and proteins into simple soluble inorganic compounds. A lot of the chemical energy in the organic compounds is lost as unstable heat energy. The decomposers only absorb a small amount of nutrients and energy for their use.

The rest is released into the soil, air and water. When decomposers die, other decomposers feed on them. The nutrient released are used by plants to manufacture their food.

Products released during decomposition are gases such as carbon dioxide, hydrogen sulphide, ammonia and water vapour. Others are heat energy and nutrients such as nitrates, sulphates and phosphate ions.


Roles of Decomposers in Ecosystem

Decomposers play major roles in the ecosystem in the following ways:

  1. They enrich the soil with nutrients required for plant growth.
  2. They contribute to environmental pollution.
  3. Decomposition is useful in the making of cheese and yoghurt.
  4. They allow the ecosystem to function by enabling the recycling of nutrients.
  5. They also prevent an unsightly accumulation of remains and wastes of living organisms on earth surface.


Experiment 1

Aim: To show that carbon dioxide is released during decomposition;

Materials required: Two test tubes, delivery tube, decaying humus, lime water;

Method: The experiment labelled test tube A is set up as shown in (Figure 24.9). Another one labelled test tube B is set up as control experiment with no humus in the test tube. The whole experiment is allowed to stand or remain for about 3-4 hours. .

Observation: It is observed that the lime water in test tube A turns milky while that of test tube B (control experiment) remains the same.


Conclusion: Since the lime water turns milky, it shows that carbon dioxide is released during decomposition.

Note: Flyrdogen suiphide (a product of decomposition) can be identified by smell. Its smell is like a rotten egg.


Experiment 2

Aim: To show that heat is released during decomposition.

Materials required: Two vacuum flasks, moist humus and two thermometers.

Method: Place moist humus in a dry vacuum flask labelled X; cover the mouth with cotton wool and insert a thermometer. Also cover the mouth of a similar vacuum flask labelled V with cotton wool and insert a thermometer (this serves as control). Allow the two flasks to remain for about 3-4 hours.

Observation: The thermometer readings are taken. It will be observed that the reading taken from flask X is higher while that of flask V is very low.

Conclusion: The experiment shows that heat was released during decomposition of humus.

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