Correct Option
The correct option is Chlorophyll a.
Explanation
Photosynthesis in higher plants occurs within the thylakoid membranes of chloroplasts, where pigments are organized into functional units called photosystems (Photosystem I and Photosystem II). Each photosystem consists of a light-harvesting complex (antennae) and a central reaction centre.
Detailed Analysis
- Chlorophyll a: This is the primary photosynthetic pigment found in all oxygen-evolving photosynthetic organisms. In the reaction centre of both Photosystem I (P700) and Photosystem II (P680), a specific pair of Chlorophyll a molecules functions as the reaction centre. It is the unique pigment capable of releasing an excited electron, thereby directly converting light energy into chemical energy.
- Chlorophyll b, Xanthophylls, and Carotenes: These are classified as accessory pigments. They absorb light at wavelengths where Chlorophyll a is less efficient and transfer the energy to the Chlorophyll a molecules in the reaction centre. While they broaden the spectrum of light absorption and protect against photo-oxidation, they do not constitute the reaction centre itself.
Key Takeaway: Chlorophyll a is the chief pigment that forms the reaction centre in photosystems, acting as the primary agent for the conversion of light energy to chemical energy.