Question

Answer all of the following questions to get full credit for the assignment. No late assignments will be accepted.

Complete the following table about the stages of photosynthesis.

Stage	Location	Reactants	Products
Light Reactions
Calvin Cycle

1) Which pigment is directly involved in the light reactions of photosynthesis?

2) What role does the pigment play in the light reactions?

3) What is the function of photosystem I?

4) What is the function of photosystem II?

5) What is the purpose of the proton gradient that is created by chemiosmosis? In what other metabolic pathway does similar chemiosmosis occur?

6) What is the benefit of photosynthesis creating some ATP by oxidative phosphorylation?

7) What are the final electon acceptors in the light reactions, and where are the electrons utilized?

Answer 1

1. Clorophyll A is directly involved in photosynthesis.

2. The pigments help in absorption of light and transferring the light energy to the reaction center where excitation of electron takes place.

3. Photosystem-I Helps in re-excitation of the electrons by absorbing photos. They absorb the light at 700nm. They mediate light-driven electron transport from electron carrier NADP+.

4. Photosystem-II is the where the absorption of light takes place. This initiates the excitation of high-energy electrons from the reaction center in non-cyclic light reaction.

5. The proton gradient that is created by electron transport favours the synthesis of ATP. This occurs when the protons move along their concentration gradient through ATP synthase. The process is called Chemiosmosis coupling. Similar mechanism is seen in aerobic cellular respiration.

6. The ATP synthesized during photosynthesis (light reaction) is utilized for reducing CO2 to sugars in the dark reaction.

7. The final electron acceptor is NADP+ which is then reduced to NADPH. These electrons are utilized in the dark reaction (Calvin cycle) to fix CO2.