Chlorophyll

Chlorophyll is the green photosynthetic pigment present in chloroplasts which provides the energy necessary for photosynthesis. The intense green color of chlorophyll is due to its strong absorbencies in the red and blue regions of the electromagnetic spectrum, and because of these absorbencies the light it reflects and transmits appears green. It is capable of channeling the energy of sunlight into chemical energy through the process of photosynthesis. In this process the energy absorbed by chlorophyll transforms carbon dioxide and water into carbohydrates and oxygen.

Table of contents

1 Chemical structure 2 Absorbance spectra 3 Evidence for chorophyll 4 Forms of chlorophyll

Chemical structure

Chlorophyll is a chlorin pigment, related to the porphyrin containing iron compound known as Heme. At the center of the ring is a magnesium ion. The side chains vary somewhat between the different forms of chlorophyll found in different organisms - chlorophyll a is always present, but chlorophylls b and c also occur in various groups.

Common structure of chlorophyll a and b

Absorbance spectra

Absorbance of light of chlorophyll a(green) and b(red)

Evidence for chorophyll

It can be shown that chlorophyll is vital for photosynthesis by destarching a variegated plant's leaves and exposing it to light for several hours. Variegated plant leaves have green areas which contain chlorophyll and white areas that have none. When tested with iodine solution a colour change showing starch present is only evident in regions of the plant that were green and therefore contained chlorophyll. This shows that photosynthesis does not occur in areas where chlorophyll is absent, and therefore supports the theory that the presence of chlorophyll is a requirement for photosynthesis to take place.

Forms of chlorophyll

Chlorophyll consists of two forms, A and B.

A: C₆₆H₇₂O₅N₄Mg

B: C₆₆H₇₀O₆N₄Mg

In both cases the magnesium atom is central in the molecule.