Question

climate and the carbon cycle
before the presence of fungi and land plants, earth’s atmosphere was very different than what it is now. it contained high levels of carbon dioxide, which kept earth’s surface temperature higher than it is today. the early appearance of fungi and land plants are linked to many changes, including changes to the chemical composition of the atmosphere. these changes made life possible for a wide range of new organisms.
these new organisms could perform functions that more primitive organisms could not. plants used the abundant carbon dioxide, combined with water, to create energy for cellular processes through photosynthesis. photosynthesis released oxygen into an atmosphere that typically contained only 5% oxygen gas. lichen, a type of fungi, lived symbiotically with photosynthesizing organisms, like algae. they produced acids that dissolved the rocks upon which they lived. these deposits, carried toward the ocean by rainfall, would bond with dissolved carbon dioxide and water (carbonic acid) and eventually create calcium carbonate. this prevented carbon atoms from forming carbon dioxide and therefore reduced the amount of carbon dioxide in the atmosphere of the prehistoric period. figure 1 illustrates this process.
figure 1.
lichen/fungi/algae
complex
which two descriptions of plants explain how they contributed to the carbon cycle?
a. plants stored carbon in their tissues to use as energy
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b. plants released calcium ions from rock to form calcium carbonate.
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c. plants combined calcium ions with carbon dioxide to make calcium carbonate.
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d. plants took in carbon dioxide and released oxygen through photosynthesis.
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e. plants broke down calcium carbonate in water to release carbon dioxide.
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Explanation:

To determine the correct answers, we analyze each option based on the carbon cycle and plant processes:

• Option A: Storing carbon in tissues is part of how plants sequester carbon, contributing to the cycle by removing CO₂ from the atmosphere and storing it. This is a valid contribution.
• Option B: Plants do not release calcium ions from rock to form calcium carbonate directly; this is more related to geological or microbial processes, not typical plant carbon cycle contributions.
• Option C: Plants do not combine calcium ions with CO₂ to make calcium carbonate (this is more associated with marine organisms or geological processes).
• Option D: Photosynthesis involves plants taking in CO₂ (carbon dioxide) and releasing O₂ (oxygen). This is a core process of the carbon cycle, as it removes CO₂ from the atmosphere.
• Option E: Breaking down calcium carbonate in water to release CO₂ is not a typical plant process (plants do not break down calcium carbonate; this is more related to weathering or marine processes).

Thus, the two correct options are A (storing carbon in tissues) and D (photosynthesis taking in CO₂ and releasing O₂).

Answer:

A. Plants stored carbon in their tissues to use as energy
D. Plants took in carbon dioxide and released oxygen through photosynthesis