Photosynthesis – class 11 revision notes

Last updated on February 5th, 2022 at 04:48 am

Pigment

A pigment is a substance that absorbs light of some wavelengths but not others. The wavelengths that it does not absorb are reflected from it.

Chlorophyll is the main pigment contained in chloroplasts. It looks green because it reflects green light. Other wavelengths (colors) of light are absorbed.

Figure 2 shows the wavelengths of light absorbed by the various pigments found in chloroplasts. These graphs are called absorption spectra.

Chlorophyll a is the most abundant pigment in most plants. Its absorption peaks are 430 nm (blue) and 662 nm (red). It emits an electron when it absorbs light.

Chlorophyll b is similar to chlorophyll a, but its absorption peaks are 453 nm and 642 nm. It has a similar role to chlorophyll a, but is not as abundant.

Carotenoids are accessory pigments. They are orange pigments that protect chlorophyll from damage by the formation of single oxygen atoms (free radicals).

They can also absorb wavelengths of light that chlorophyll cannot absorb, and pass on some of the energy from the light to chlorophyll.

Xanthophylls are also accessory pigments, capturing energy from wavelengths of light that are not absorbed by chlorophyll.

*Important production of ATP is called photophosphorylation