Question

keystone practice exam
which of the following is true about plants and cellular energy?
possible points: 1
plants can use light energy to produce food molecules or to obtain cellular energy from the bonds of these food molecules during photosynthesis.
plants use light energy to produce food molecules during cellular respiration and to obtain cellular energy from the bonds of these food molecules during photosynthesis.
plants use light energy to produce food molecules during photosynthesis and obtain cellular energy from the bonds of these food molecules during cellular respiration.
plants can use light energy to produce food molecules or to obtain cellular energy from the bonds of these food molecules during cellular respiration.

Explanation:

To solve this, we recall the processes of photosynthesis and cellular respiration in plants:

• Photosynthesis: Plants use light energy (from the sun) to convert carbon dioxide and water into glucose (food molecules) and oxygen. The equation is \(6CO_2 + 6H_2O \xrightarrow[\text{Chlorophyll}]{\text{Light Energy}} C_6H_{12}O_6 + 6O_2\).
• Cellular Respiration: Plants (and all living cells) break down glucose (food molecules) to release energy (ATP) for cellular work. The equation is \(C_6H_{12}O_6 + 6O_2

ightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}\).

Now let's analyze each option:

• First option: Photosynthesis is for producing food (glucose), not for obtaining energy from food bonds. Cellular respiration is for that. So this is incorrect.
• Second option: Photosynthesis produces food, cellular respiration breaks it down. The processes are mixed up here. So incorrect.
• Third option: This matches the definitions. Photosynthesis makes food with light, respiration breaks food bonds for energy. Correct.
• Fourth option: Cellular respiration does not use light energy to produce food or to get energy (it breaks food bonds). Photosynthesis uses light. So incorrect.

Answer:

The correct option is: Plants use light energy to produce food molecules during photosynthesis and obtain cellular energy from the bonds of these food molecules during cellular respiration. (The third option among the given choices)