Explanation:

The absorption peak of chlorophyll a in the reaction center of Photosystem I (PSI) is at 700nm. This means that chlorophyll a molecules in PSI can absorb light most efficiently at a wavelength of 700nm.

Photosystem I (PSI):
- PSI is one of the two photosystems found in the thylakoid membrane of chloroplasts.
- It is responsible for the absorption of light and the transfer of electrons during the light-dependent reactions of photosynthesis.
- PSI contains chlorophyll a molecules in its reaction center, which are responsible for capturing light energy.

Chlorophyll a:
- Chlorophyll a is a pigment found in chloroplasts that plays a crucial role in photosynthesis.
- It absorbs light energy and transfers it to other molecules in the photosystems.
- Chlorophyll a is the primary pigment in PSI and PSII, and each has a characteristic absorption peak.

Absorption peak of chlorophyll a in PSI:
- The absorption peak of chlorophyll a in PSI is at 700nm.
- This means that chlorophyll a molecules in PSI can absorb light most efficiently at a wavelength of 700nm.
- Light with a wavelength of 700nm corresponds to red light, which is why PSI is often referred to as a P700 photosystem.

Significance of the absorption peak:
- The absorption peak of chlorophyll a in PSI at 700nm is important for the efficient capture of light energy during photosynthesis.
- This wavelength of light is abundant in sunlight, allowing PSI to harvest light energy effectively.
- The absorbed light energy is then used to drive the transfer of electrons through a series of electron carriers in PSI, leading to the generation of ATP and the reduction of NADP+ to NADPH.

In summary, the absorption peak of chlorophyll a in the reaction center of PSI is at 700nm. This allows PSI to efficiently capture light energy at this wavelength, which is crucial for the process of photosynthesis.