3.8 Photosynthesis
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8 terms
Terms | Definitions |
|---|---|
 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. |
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