What key role do chloroplasts play in plants?

Chloroplasts are essential organelles found in the cells of green plants and some algae. Their primary function is to convert light energy from the sun into chemical energy through the process of photosynthesis. In this process, chloroplasts capture sunlight and utilize it to transform carbon dioxide and water into glucose, which serves as an energy source for the plant. This light energy conversion is crucial not only for the plant's growth and energy needs but also for providing oxygen as a byproduct, which is vital for the survival of most living beings on Earth.

While chloroplasts are involved in some aspects of the other functions listed—such as carbon fixation, which occurs during the photosynthesis process—their main and most defining role is the conversion of light energy into a usable form for the plant. The other options mentioned, such as nutrient storage and water absorption, are handled by different structures and systems within the plant. Thus, the ability of chloroplasts to harness light energy is fundamental to plant survival and growth.