3.8.1 State that photosynthesis involves the conversion of light energy into chemical energy.
Photosynthesis involves energy conversion. Light energy, usually sunlight, is converted into chemical energy.
3.8.2 State that white light from the sun is composed of a range of wavelengths.
Sunlight is called white light, but it is actually made up of a range of wavelengths including red, blue, and green.
3.8.3 State that chlorophyll is the main photosynthetic pigment
The structure of chlorophyll allows it to absorb some colours of wavelength better than others.
3.8.4Outline the differences in absorption of red, blue and green light by chlorophyll
Red and blue light are absorbed more than green. The green light that cannot be absorbed is reflected giving plants (and the pigment chlorophyll) their green colour.
3.8.5 State that light energy is used to split water molecules (photolysis) to give oxygen and hydrogen and to produce ATP
* Some of the energy absorbed by chlorophyll is used to produce ATP
* Some of the energy absorbed by chlorophyll is used to split water molecules. This is called photolysis of water
* Photolysis of water results in the formation of oxygen and hydrogen. The oxygen is released as a waste product
3.8.6 State that ATP and hydrogen (derived from photolysis of water) are used to fix carbon dioxide to make organic molecules.
* Carbon dioxide is absorbed for use in photosynthesis
* The carbon from it is used to make a wide range of organic substances
* The conversion of carbon in a gas to carbon in solid compounds is called carbon fixation
* Carbon fixation involves the use of hydrogen from photolysis and energy from ATP.
3.8.7 Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by the increase of biomass
* Uptake of carbon dioxide: Since carbon dioxide is important in the light-independent reactions of photosynthesis, its consumption by plants can be measured as a means to determine the rate of ATP and electron carriers used for carbon fixation.
* Production of oxygen: Aquatic plants release bubbles of oxygen when they carry photosynthesis. e.g. these bubbles are collected; their volume can be measured.
* Increase in Biomass: If batches of plants are harvested at a series of times and their biomass determined, then the rate of photosynthesis can be determined by an increase in biomass.
Outline the effects of temperature, light intensity, and carbon dioxide concentration on the rate of photosynthesis:
* Light - At low medium light intensities the rate is directly proportional to light intensity. At high light intensities the rate reaches a plateau.
* Carbon Dioxide - No photosynthesis at very low CO2 concentrations. At low to fairly high CO2 concentrations the rate is positively correlated with CO2 concentration. At very high CO2 concentrations the rate reaches a plateau.
* Temperature - As temperature increases the rate increases more and more steeply. If the temperature increases with 10¤C it roughly doubles the rate. When it reaches it maximum point it is said to be its Optimum Temperature which is around 40¤C. Above the optimum temperature the rate slows down rapidly and then stops. This happens because the excessive heat destroys the enzymes which are responsible for catalyzing chemical reactions.