Increasing Soil Fertility and Cleaning the Environment - NCERT

If we look at the water droplets in a pond under a microscope, we will see many small round structures. These tiny creatures are known as microbes or microbes. They are all around us and are too small to be seen with the naked eye. Microorganisms are classified into four groups:

1. Protozoa: Protozoa are single-celled animals. Some live free, others become parasites. Some parasitic protozoa cause diseases in humans, livestock, and plants. For example, the protozoan Plasmodium malaria causes malaria. 
2. Bacteria: Bacteria are single-celled microorganisms that belong to the plant kingdom and have a rigid cell wall similar to plant cells. 
3. Fungi:Fungi are unicellular (yeast) and multicellular (Penicillium) organisms. These organisms are eukaryotes because their cells have nuclei. They grow on dead or decomposing organic material. Unlike plant cells, fungi lack chlorophyll. 
4. Algae: Algae are green substances that float on the surface of ponds, lakes, rivers, stagnant water, moist soil, and rocks. They tend to grow on damp surfaces. Therefore, they can synthesize their food. They can be found underwater or in very humid areas.

Increasing Soil Fertility

Soil fertility is the ability of soil to support plant growth by providing essential plant nutrients and favorable chemical, physical and biological parameters.

The process of converting nitrogen present in the air to ammonia or other nitrogen-containing compounds is known as "nitrogen fixation" and is done by Microorganisms. Microbes in the soil feed on dead plant and animal matter to form humus, rich in nutrients, and make the soil fertile. Microorganisms such as algae, bacteria, and fungi are present in the soil. Bacteria and fungi present in the soil feed on dead plant and animal matter to form humus, which is rich in nutrients and makes the soil fertile. This is how microorganisms make the soil fertile. Thus, we can say that soil becomes barren when nutrients in the soil exceed or decrease in optimal levels. 

Example: Rhizobium is an example of a commensal bacterium that attaches to legume roots and increases soil fertility by converting atmospheric nitrogen into organic compounds.

Cleaning the Environment

Microbes help clean the environment by breaking down dead and decaying organic matter. It not only breaks down dead matter but also removes microorganisms from the organic waste produced in the environment. These microorganisms gain "energy and nutrients" by cleaning up this organic waste. If they are not available, there is no recycling in the ecosystem. Microorganisms such as bacteria and fungi play a major role in the decomposition of spoilage. Dead animals and plants contribute to the pollution of the environment and also produce foul odors. Breaking down the same helps clean up the environment. Microorganisms eat dead plants and animals, decompose them, and transform them into simpler compounds making them nontoxic and odorless. These compounds are then mixed into the soil and used by other plants and animals.