Question

Compare and contrast the electron transport chains in respiration and photosynthesis, for example noting differences in source of electron and electron energy, location in organelles, role and direction of H+ movement, role of oxygen/water, etc. [Analysis]

Answer 1

In respiration, electrons come from NADH and FADH2 and the electron energy comes from the breakdown of glucose, while in photosynthesis, electrons come from water and the electron energy comes from light. The electron transport chain is located in the inner membrane of mitochondria in respiration and in the thylakoid membrane of chloroplasts in photosynthesis. H+ ions are pumped across a membrane in both processes, creating a chemiosmotic gradient that is used to generate ATP. Oxygen serves as the final electron acceptor in respiration, forming water, while in photosynthesis, water is split to provide electrons for the electron transport chain.

Step-by-step explanation:

In both respiration and photosynthesis, electron transport chains are used to transfer energy-carrying electrons from one molecule to another. However, there are some key differences between the two processes:

1. Source of electron: In respiration, the source of electrons is NADH and FADH2, which are produced during glycolysis and the Krebs cycle. In photosynthesis, the source of electrons is water.
2. Source of electron energy: In respiration, the electron energy comes from the breakdown of glucose. In photosynthesis, the electron energy comes from light.
3. Location in organelles: In respiration, the electron transport chain is located in the inner membrane of the mitochondria. In photosynthesis, the electron transport chain is located in the thylakoid membrane of the chloroplasts.
4. Role and direction of H+ movement: In both processes, the movement of electrons along the electron transport chain leads to the pumping of H+ ions across a membrane. This creates a chemiosmotic gradient that is used to generate ATP. The direction of H+ movement is from the mitochondrial intermembrane space (respiration) or the thylakoid space (photosynthesis) to the matrix (respiration) or the stroma (photosynthesis).
5. Role of oxygen/water: In respiration, oxygen serves as the final electron acceptor at the end of the electron transport chain, forming water. In photosynthesis, water is split during the light reactions and provides the electrons needed for the electron transport chain.