Question

Choose the correct statement(s) from the following about chlorophyll :
I. Four pyrrole rings are attached to Mg by their C atoms
II. Cyclopentanone ring is attached to the tetra-isoprenoid alcohol chain.
III. Chlorophyll appears green due to absorption of red and blue light.
IV. Excitation of chlorophyll by light is a photochemical reaction

• A. I, II, III
• B. III, IV
• C. I, II, IV
• D. II, III,IV

Answer 1

The correct option is B III, IV

In a chlorophyll molecule,

• there are four pyrrole rings which are attached to the central Mg2+ ion by their N atom and not C atoms.
• the fourth pyrrole ring is attached to the tetra-isoprenoid alcohol chain. Cyclopentanone ring is attached to the third pyrrole ring but not to the tetra-isoprenoid alcohol chain.

Chlorophyll is a light absorbing pigment and it absorbs strongly in blue-violet (~450 nm) and red regions (~680 nm) of the spectrum. There are different types of chlorophyll molecules:

• Chlorophyll a absorbs maximum at 430 nm and 660 nm.
• Chlorophyll b absorbs maximum at 463nm and 643 nm.

It reflects only some light enriched in green wavelength (~550 nm). So, it appears green in colour.

Excitation of chlorophyll by light of wavelength in blue-violet and red region causes excitation and eventual loss of electrons. This oxidises chlorophyll molecule and hence, it is a redox chemical reaction which is driven by sunlight.