The carbon cycle

Question 1

Describe the carbon cycle (8)

Answer 1

• carbon dioxide in air is absorbed during photosynthesis and converted to glucose
• carbon compounds in plants are passed to animals when they eat them
• animals and plants respire, returning CO2 into the air
• are then passed from animal to animal
• dead plants and animals are eaten by decomposers, such as bacteria and fungi, which releases CO2 from their respiration
• dead organisms that are not broken down by decomposers may eventually form fossil fuels
• when fossil fuels are burnt the carbon they contain is released back into the air as CO2
• some of the CO2 dissolves in water

Question 2

What is carbon in organisms a part of?

Answer 2

complex carbon compounds

Question 3

Why is the carbon cycle important?

Answer 3

it recycles carbon dioxide released in respiration to be taken in by plants in photosynthesis, to make organic molecules in living organisms

Question 4

A large forest is cleared by burning. What effects will this have on the amount of carbon dioxide in the air a) immediately and b) over a longer period? [4]

Answer 4

a) large amounts of carbon dioxide will be released into the air by the combustion of the trees
b) less carbon dioxide will be removed from the air than before because the trees would have used some for photosynthesis. So the amount of CO2 in the air is likely to remain high.

Question 5

Describe the importance of decomposers in the carbon cycle. [1]

Answer 5

decomposers release carbon back into the air as CO2 from respiration

Question 6

Explain the effect of respiration, photosynthesis and combustion in the carbon cycle in transferring CO2 to and from the atmosphere [3]

Answer 6

respiration releases carbon from compounds in living organisms as CO2 gas into the air

photosynthesis takes CO2 from the air and converts it into carbon compounds in plants

combustion releases carbon from compounds in fossil fuels into CO2 in the air