1 Draw a well labelled diagram to show carbon cycle in nature.

2What causes acid rain?

3What is humus? What is its function in the soil?

4What is biological fixation? How is it different from nitrification? Give an E.g. Of organism involved in each of these?

5What is contribution of photosynthesis in carbon cycle?

6Draw a well labelled diagram to show N2 cycle in nature?

Acid rain is caused when the oxides of nitrogen and sulphur are precipitated from the rain water. These oxides are present in the upper atmosphere and when rain falls these oxides get dissolved in rain water and forms nitric acid and sulphuric acid thus makes it acidic.

Humus refers to any organic matter that reached a point of stability where it will not break down further. It might be remain as such if the conditions does not change .

Uses :- 1) Used to retain the soil moisture and encourage the formation of the good soil structure.

2) Humus also bind the plant nutrients , making them more available to the plants.

3) In the agriculture humus is sometimes use to describe mature compost or natural compost extracted from the forest and the other spontaneous source.

4) It is also used to describe topsoil horizon that contains organic matter.

Biological fixation is a process in which, molecules existing in nature are fixed or hold by an  organism via  biological methods and are converted  into usable forms.

For example- Nitrogen fixation in which, certain forms of bacteria (Rhizobium) are able to convert atmospheric nitrogen into usable forms such as nitrates and nitrites. These usable forms of nitrogen are absorbed by plants to produce many compounds such as amino acids, which in turn form proteins.

Biology plays an important role in the movement of carbon between land, ocean, and atmosphere through the processes of photosynthesis and respiration . Virtually all multicellular life on Earth depends on the production of sugars from sunlight and carbon dioxide (photosynthesis) and the metabolic breakdown (respiration) of those sugars to produce the energy needed for movement, growth, and reproduction. Plants take in carbon dioxide (CO₂) from the atmosphere during photosynthesis, and release CO₂ back into the atmosphere during respiration.