The carbon cycle recycles carbon between the atmosphere, living organisms and the environment. Carbon moves between these stores as organisms feed, respire ...
Question 1 Report
The carbon cycle recycles carbon between the atmosphere, living organisms and the environment. Carbon moves between these stores as organisms feed, respire and die, and as fuels are burned. Fig. 1.1 is a diagram of the carbon cycle. Two of the processes are labelled A and B, and the diagram also shows plants, animals, decomposers and fossil fuels.
(a) State the name of the gas, present in the atmosphere, that is cycled in the carbon cycle. [1]
(b) Name the processes labelled A and B on Fig. 1.1. [2]
(c) Describe the part played by decomposers in returning carbon to the atmosphere. [3]
(d) Explain how the burning of fossil fuels can lead to an increase in the Earth's temperature. [4]
(e) State two ways, other than decomposition, by which carbon dioxide is added to the atmosphere. [2]
(f) Suggest two ways in which humans could reduce the amount of carbon dioxide released into the atmosphere. [2]
Answer Details
(a) The atmospheric gas cycled in the carbon cycle is carbon dioxide [1].
(b) The labelled processes are: A = photosynthesis (removes carbon dioxide from the air into plants) [1]; B = respiration (returns carbon dioxide to the air) [1].
(c) Decomposers return carbon to the air because decomposers (bacteria and fungi) feed on / break down dead organisms and waste [1]; as they do so they respire [1], which releases carbon dioxide back into the atmosphere [1].
(d) Burning fossil fuels can raise Earth's temperature because fossil fuels contain carbon (locked up from ancient organisms) [1]; combustion releases this as carbon dioxide [1]; carbon dioxide is a greenhouse gas that absorbs / traps heat re-radiated from the Earth's surface [1]; the resulting enhanced greenhouse effect raises the global temperature [1].
(e) Two ways, other than decomposition, that add carbon dioxide to the air: respiration (of plants and animals) [1]; combustion / burning of fuels [1].
(f) Two ways humans could reduce carbon dioxide released (1 each): burn less fossil fuel / use renewable energy sources [1]; plant more trees and reduce deforestation (so more CO2 is removed by photosynthesis) [1] (max 2).
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