Question

how does the presence of carbon dioxide in earths atmosphere support life?
a. it is used by plants to produce oxygen through photosynthesis.
b. it is the main gas animals use for respiration.
c. it blocks harmful ultraviolet radiation from the sun.
d. it is the primary source of nitrogen for plants.

Explanation:

• Option A: Photosynthesis in plants uses carbon dioxide ($\ce{CO_2}$) and water to produce glucose and oxygen ($\ce{O_2}$), which is essential for life (animals use $\ce{O_2}$ for respiration).
• Option B: Animals use oxygen, not carbon dioxide, for respiration.
• Option C: Ozone (not carbon dioxide) blocks harmful UV radiation.
• Option D: Carbon dioxide provides carbon, not nitrogen, for plants. Nitrogen is obtained from nitrogen - fixing processes or fertilizers. So the correct option is A.

Answer:

A. It is used by plants to produce oxygen through photosynthesis.