What is the major difference between chloroplasts and mitochondria in energy metabolism?

• A. Chloroplasts harvest energy from organic molecules to produce ATP; mitochondria capture light energy to synthesize sugars and produce ATP and NADPH.
• B. Mitochondria harvest energy from organic molecules to produce ATP; chloroplasts capture light energy to synthesize sugars and produce ATP and NADPH.
• C. Both organelles only produce ATP and not NADPH.
• D. Mitochondria produce NADPH and ATP from light.

Answer: (B)

The key idea is that these two organelles carry out energy metabolism in different ways because they use different energy sources. Mitochondria extract energy from organic molecules (like glucose) and convert it into ATP through cellular respiration, with electron carriers such as NADH and FADH2 driving a downstream electron transport chain. Chloroplasts, on the other hand, capture light energy in photosynthesis to drive the synthesis of sugars, and in the process they generate ATP and NADPH to power carbon fixation.

So, the major difference is the energy input and the primary products: mitochondria use chemical energy from organic compounds to make ATP, while chloroplasts use light energy to produce sugars and to generate ATP and NADPH needed for sugar synthesis.