B7.2

The equation for photosynthesis is:

                                                                 light energy

carbon dioxide (6CO2) + water (6H2O) ------------------> glucose (C6H12O6) + oxygen (6O2)

                                                                   chlorophyll

- The green chemical chlorohyll absorbs light.

- The energy is used to rearrange the atoms of carbon dioxide and water.

- The products are glucose ( a sugar ) and oxygen ( a waste product ).

- convert some of the Glucose into chemicals needed for growth, such as cellulose, protein and chlorophyll.

- convert some into starch for storage.

- use some in respiration to release energy.

Because it is insoluble Starch has little effect on the osmotic balance of cells. A high concentration of glucose causes water to be drawn into cells. Therefore starch is a better storage molecule than glucose.

Energy released in respiration is used to synthesise polymers such as:

- starch and celluse from glucose.

- Amino acids and then proteins from glucose and nitrates.

Plant roots absorb nitrates by active transport, a process that requires energy.

The rate of photosynthesis may be limited by low.

- Temperatures.

- Carbon dioxide concentraton.

- Light intensity.

The amounts of carbon dioxide and oxygen exchanged over a 24 hour period vary. At compensation points the rate of photosynthesis and respiration balance. So there is no net movement of these gases between a plant and the surrounding atmosphere.

The rate of photosynthesis is limited by the factor that is in shortest supply.