Question

when carbon dioxide levels in earth’s atmosphere declined, the climate on earth changed even more. between 750 million and 580 million years ago, temperatures dropped around the globe. this period was characterized by short - term earth experienced a period called snowball earth, in which earth’s surface was covered primarily with snow and ice. then, roughly 530 million years ago, earth went through the cambrian explosion. the new atmosphere, rich in oxygen gas from photosynthesis in land plants, spurred the evolution of sophisticated organisms, some of which had skeletons. figure 2 illustrates the relationship between atmospheric carbon dioxide and surface temperature.
figure 2.
which two descriptions of plants explain how they contributed to the carbon cycle?
a. plants stored carbon in their tissues to use as energy
b. plants released calcium ions from rock to form calcium carbonate
c. plants combined calcium ions with carbon dioxide to make calcium carbonate
d. plants took in carbon dioxide and released oxygen through photosynthesis
e. plants broke down calcium carbonate in water to release carbon dioxide

Explanation:

To determine which descriptions relate to plants' contribution to the carbon cycle, we analyze each option:

• Option D: Plants perform photosynthesis, taking in \( \text{CO}_2 \) (carbon dioxide) and releasing \( \text{O}_2 \) (oxygen). This is a key part of the carbon cycle as it removes \( \text{CO}_2 \) from the atmosphere.
• Option E: Some plants (like those with carbonate skeletons) can break down calcium carbonate in water, releasing \( \text{CO}_2 \) back into the environment, contributing to the carbon cycle.

Option A is about using stored carbon as energy (more about respiration or energy use, not direct carbon cycle contribution). Option B describes releasing calcium ions to form calcium carbonate (not a typical plant - carbon cycle action). Option C is about combining calcium ions with \( \text{CO}_2 \) to make calcium carbonate, which is more related to geological or chemical processes rather than plant - driven carbon cycle processes.

Answer:

D. Plants took in carbon dioxide and released oxygen through photosynthesis
E. Plants broke down calcium carbonate in water to release carbon dioxide