Ecology and Ecosystems: Question 6
Syllabus 19.3
Carbon dioxide is constantly added to and removed from the atmosphere by different living processes in an ecosystem.
Which process releases carbon dioxide into the atmosphere and is carried out by producers, consumers and decomposers alike?
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Worked solution
Step 1: Rule out the nitrogen cycle processes
Nitrification and nitrogen fixation are both nitrogen cycle processes, carried out by particular groups of soil bacteria. Neither of them adds carbon dioxide to the atmosphere, so options C and D can be ruled out straight away.
Step 2: Compare photosynthesis and respiration
Photosynthesis is carried out only by producers (green plants and some other photosynthetic organisms). It removes carbon dioxide from the atmosphere, using it to build organic compounds, so it is the opposite of what the question describes.
Respiration, by contrast, happens continuously in the living cells of every organism: producers, consumers and decomposers all break down organic compounds to release energy, and this process releases carbon dioxide as a waste product. Because it is carried out by all three groups, respiration is the process that fits the question.
Why the other options are wrong
- A (photosynthesis): removes carbon dioxide from the atmosphere, and is carried out only by producers, not by consumers or decomposers.
- C (nitrification): a nitrogen cycle process carried out by nitrifying bacteria, converting ammonium ions into nitrite and nitrate ions; it does not involve carbon dioxide.
- D (nitrogen fixation): a nitrogen cycle process carried out by certain bacteria, converting nitrogen gas into nitrogen compounds; it also does not involve carbon dioxide.
Final answer
Respiration releases carbon dioxide into the atmosphere and is carried out by producers, consumers and decomposers alike, option B.