Quick questions on The carbon cycle explained: O-Level Biology

Carbon is present in the air as the gas carbon dioxide. The carbon cycle is the way this carbon moves between the air, living things, and the ground (including fossil fuels), being used and returned over and over.

Photosynthesis is the main process that removes carbon dioxide. Green plants take in carbon dioxide and use it to make glucose. The carbon becomes part of the plant's molecules (carbohydrates, fats and proteins). When animals eat plants, this carbon passes into animals to build their bodies (feeding).

Respiration returns carbon dioxide. All living things (plants, animals and decomposers) respire, breaking down glucose and releasing carbon dioxide back into the air.

Long ago, the remains of dead organisms that did not fully decompose were buried and, over millions of years, turned into fossil fuels. These store carbon. Burning them releases that carbon as carbon dioxide, which is why human use of fossil fuels adds extra carbon dioxide to the air.

When organisms die, decomposers (bacteria and fungi) break down the dead matter. As they feed and respire, they release the carbon as carbon dioxide back to the air.

Burning fossil fuels (coal, oil and gas) and wood releases carbon dioxide that was stored in them.

Name the process that removes carbon dioxide from the air. [1 mark]

State two processes that return carbon dioxide to the air. [2 marks]

Explain how human activity has increased the carbon dioxide in the air. [2 marks]