Gradients in Plants: Which Compartments are Responsible?

Explanation:

Chloroplasts: Chloroplasts are responsible for photosynthesis, where they use light energy to build up a proton gradient across the thylakoid membrane during the light-dependent reactions. This gradient is then used to produce ATP, which is necessary for the light-independent reactions (also known as the Calvin cycle) that take place in the stroma of chloroplasts.

Mitochondria: Similarly, mitochondria generate a proton gradient across their inner membrane during cellular respiration to produce ATP.

Given the choices provided, chloroplasts are the best answer to which compartments build up gradients in plants. To be more specific, the light-independent reactions of photosynthesis occur in the stroma of the chloroplasts.