DIFFERENCES AND SIMILARITIES BETWEEN PHOTOSYSTEM II AND PHOTOSYSTEM I

Answer 1

The main differences between Photosystem II and Photosystem I are:

1. Role in electron transport: Photosystem II (PSII) functions as the initial step in the light-dependent reactions of photosynthesis and is responsible for splitting water and generating oxygen. It also donates electrons to the cytochrome b6f complex. Photosystem I (PSI) functions afterwards and receives electrons from cytochrome b6f complex to generate NADPH.

2. Absorption peak: PSII predominantly absorbs light at a wavelength of around 680 nm, hence it is also known as P680. PSI primarily absorbs light at a wavelength of around 700 nm, hence it is also known as P700.

3. Electron acceptors: PSII transfers electrons to the plastoquinone (PQ) pool, which eventually leads to the generation of a proton gradient. PSI transfers electrons to ferredoxin, which is then utilized to reduce NADP+ to NADPH.

4. Generation of ATP: PSII indirectly contributes to the generation of ATP through the establishment of a proton gradient across the thylakoid membrane. PSI does not directly contribute to ATP production, but instead generates reducing equivalents in the form of NADPH.

The main similarities between PSII and PSI are:

1. Both photosystems are involved in the light-dependent reactions of photosynthesis.

2. They both consist of a core complex composed of chlorophyll molecules that absorb light energy.

3. Both photosystems contain accessory pigments such as carotenoids and phycobilins to expand the spectrum of light they can absorb.

4. Both photosystems involve the transfer of excited electrons through a series of electron acceptors to generate energy-rich molecules like ATP and NADPH.

5. They both contribute to the overall goal of photosynthesis, which is to convert light energy into chemical energy in the form of ATP and NADPH, which are subsequently used in the Calvin cycle for carbon fixation.