(a) With the aid of a fully labelled diagram, describe the carbon cycle. (b) Explain the importance of carbon cycle to Crops and animals

(a) Carbon cycle

The carbon cycle is the continuous movement of carbon between the atmosphere, green plants, animals, soil organisms and the earth. The diagram below shows the main processes involved.

Description:

1. Carbon occurs in the atmosphere mainly as carbon dioxide, CO₂.
2. Green plants absorb atmospheric CO₂ during photosynthesis and use it to manufacture carbohydrates and other organic compounds.
3. Carbon passes from plants to animals when animals feed on plants or on other animals.
4. Plants, animals and microorganisms release CO₂ back into the atmosphere during respiration.
5. When plants and animals die, their remains and wastes enter the soil as dead organic matter. Decomposers act on this material and release CO₂ by decomposition.
6. Some buried organic remains may, over a very long period, form fossil fuels. Combustion of wood and fossil fuels releases CO₂ to the atmosphere.

(b) Importance of the carbon cycle to crops and animals

1. It maintains a continuous supply of atmospheric CO₂ needed by green plants for photosynthesis.
2. Photosynthesis converts CO₂ into carbohydrates such as glucose and starch, which provide food and energy for crop growth.
3. Carbon fixed by crops becomes part of proteins, fats, carbohydrates and other organic substances in plant tissues.
4. Animals obtain carbon-containing food materials by feeding on plants or other animals; these materials are needed for energy, growth, repair and reproduction.
5. Respiration by plants, animals and microorganisms, together with decomposition and combustion, returns CO₂ to the air, thereby maintaining the carbon dioxide supply for crops.
6. Decomposition of crop and animal residues adds organic matter to the soil, improving soil structure and helping to maintain soil fertility.
7. The cycle helps to maintain the balance of oxygen and carbon dioxide in the atmosphere: plants release oxygen during photosynthesis, while animals and plants release carbon dioxide during respiration.