Question

electron transport step energy input required? 1. water → p680+ 2. p680 → pq (plastoquinone) 3. pq → p700+ 4. p700 → fd (ferredoxin) 5. fd → nadp+ no energy input required energy input required

Explanation:

Step1: Analyze step 1

In the reaction \(Water \to P680^{+}\), water is oxidized. This is part of the light - dependent reactions in photosynthesis. The energy for this comes from light (photons) absorbed by photosystem II. So, energy input (light energy) is required.

Step2: Analyze step 2

For \(P680 \to Pq\) (plastoquinone), \(P680\) is a reaction - center chlorophyll in photosystem II. After absorbing light energy (which was used in step 1 for water oxidation), the excited electron is transferred to plastoquinone. The energy for this electron transfer was already provided by light energy in the initial excitation of \(P680\), so no additional energy input is required for just the electron transfer from \(P680\) to \(Pq\).

Step3: Analyze step 3

For \(Pq \to P700^{+}\), \(Pq\) transfers electrons through the cytochrome complex. The electrons then reach photosystem I (\(P700\)). But to create \(P700^{+}\) (a positively charged \(P700\)), light energy is absorbed by photosystem I. This light energy causes the electron to be removed from \(P700\) (forming \(P700^{+}\)), so energy input (light energy) is required.

Step4: Analyze step 4

For \(P700 \to Fd\) (ferredoxin), after \(P700\) absorbs light energy (used for its excitation), the excited electron is transferred to ferredoxin. The energy for this electron transfer was provided by the light - induced excitation of \(P700\), so no additional energy input is required for just the electron transfer from \(P700\) to \(Fd\).

Step5: Analyze step 5

For \(Fd \to NADP^{+}\), the enzyme \(NADP^{+}\) reductase catalyzes the transfer of electrons from ferredoxin (\(Fd\)) to \(NADP^{+}\) to form \(NADPH\). This reaction is coupled with the proton gradient (from the electron - transport chain) and does not require an additional direct energy input (like light) at this step.

Answer:

1. energy input required
2. no energy input required
3. energy input required
4. no energy input required
5. no energy input required