chlorophyll

A chloroplast is shaped like a flattened disc, with a double membrane enclosing the gel-like stroma. The stroma contains cavities, or vesicles, where photosynthesis occurs.

Group of pigments including chlorophyll a and chlorophyll b, the green pigments present in chloroplasts in most plants; it is responsible for the absorption of light energy during photosynthesis. The pigment absorbs the red and blue-violet parts of sunlight but reflects the green, thus giving plants their characteristic colour. Other chlorophylls include chlorophyll c (in brown algae) and chlorophyll d (found in red algae).

Chlorophyll is found within chloroplasts, present in large numbers in leaves. Cyanobacteria and other photosynthetic bacteria also have chlorophyll, though of a slightly different type. Chlorophyll is similar in structure to haemoglobin, but with magnesium instead of iron as the reactive part of the molecule. Because magnesium is contained in chlorophyll it is considered an essential plant mineral salt. Magnesium can often be a part of a mixture of minerals used as a fertilizer.