Science of food production

The human population is increasing and this increases demand for food. Farmers can alter genes, control pests and ensure acceptable well-being to increase yields of plants and livestock.

Plant growth and productivity


Photosynthesis is the process by which green plants trap light energy and use it to make carbohydrates.

When light strikes a leaf, some (12 per cent) is reflected, some (5 per cent) is transmitted through the leaf and the rest (83 per cent) is absorbed by the pigments within the chloroplasts.


Pigments are chemicals found within the chloroplasts which absorb light energy and convert it to chemical energy. The principal pigments are chlorophyll a and b - they mainly absorb light in the red and blue wavelengths of light.

Plants also contain carotenoids (carotene and xanthophyll) which absorb light from other regions of the spectrum and pass the energy on to chlorophyll a.

Absorption and action spectrum

The absorption spectrum (graph A) shows the wavelengths of light absorbed by the different pigments in a leaf. The action spectrum (graph B) shows how effective the different wavelengths of light are at photosynthesis.

Graph A

Absorption spectrum graph

Graph B

Action spectrum graph

Having multiple photosynthetic pigments increases the range of wavelengths of light that the plant can absorb and so increases the level of photosynthesis.