S-Cool Revision Summary

S-Cool Revision Summary

Chlorophyll absorbs light from the visible part of the electromagnetic part of the spectrum, but there are several types of chlorophyll...

chlorophyll a

chlorophyll b

chlorophyll c

bacteriochlorophyll (found in photosynthetic bacteria!)

There are also other families of pigments, such as the carotenoids.

Not all wavelengths of light are equally absorbed and different chlorophylls absorb more strongly in different parts of the visible spectrum.

The pigments are arranged in funnel shaped photosystems that sit on the thylakoid membranes in the chloroplasts.

In each photosystem, several hundred pigment molecules, called accessory pigments, are clustered around a particular pigment molecule, known as the primary pigment.

The various accessory pigments absorb light of different wavelengths and pass the energy down the photosystem. Eventually the energy reaches the primary pigment that acts as a reaction centre.

There are 2 types of photosystem:

Photosystem One - PS I:

Its primary pigment is a molecule of chlorophyll a with an absorption peak at 700nm. It is called P700

Photosystem Two - PS II:

Its primary pigment is a molecule of chlorophyll b with an absorption peak at 680nm. It is called P680

The first reactions of photosynthesis require light energy, and are called light dependant reactions.

The aim is to produce ATP from ADP and inorganic P and harvest hydrogen so that carbon dioxide can be reduced to form a carbohydrate in the second series of reactions. The production of ATP using light is called photophosphorylation.

Calvin cycle

These reactions can occur in the light or the dark. They need ATP for energy to drive the reactions, and they need NADPH for reducing power. They occur in the stroma of the chloroplast and are called the Calvin cycle.