4.1 Photosynthesis Flashcards
Photosynthesis
Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.
The leaves of the plant are where most photosynthesis takes place, in specialised mesophyll cells which are packed with chloroplasts containing chlorophyll to absorb as much light energy as possible.
The sugars produced by photosynthesis are used to make all the substances a plant needs, as well as being used in respiration to release energy.
Carbon dioxide + water —— oxygen + glucose
6CO2 + 6H2O —— 6O2 + C6H12O6
Factors affecting the rate of photosynthesis (temperature)
Increasing temperature increases the kinetic energy of particles, increasing the number of frequent successful collisions between reactants and enzymes which results in the formation of products.
At higher temperatures, however, enzymes that control the processes of photosynthesis can be denatured (where the active site changes shape and is no longer complementary to its substrate) – this reduces the overall rate.
Factors affecting rates of photosynthesis (light intensity)
The higher the light intensity, the higher the rate until a certain point. If you increase the intensity of the light, more light can be trapped by the chloroplasts to provide energy to drive the photosynthetic reaction.
At high light intensity, rate levels off. This is because the maximum amount of light has already been trapped. When you reach this point, light is no longer a limiting factor.
Factors affecting rates of photosynthesis (CO2)
The higher the CO₂ concentration, the higher the rate until a certain point.
At high CO₂ concentration, rate levels off beacause you reach a point at which the enzymes required are saturated. At this point, the carbon dioxide is no longer a limiting factor.
Factors affecting rates of photosynthesis (chlorophyll)
As the amount of chlorophyll increases, more light can be trapped by the chlorophyll in order to drive the reaction. However, once there is a certain amount of chlorophyll, it will no longer be a limiting factor and the values of other factors will limit the rate of the reaction. Infection and disease can reduce the amount of chlorophyll in a plant.
Greenhouses
Commercial horticulturists will grow their plants in a greenhouse.
This means that they are able to control as many of the limiting factors of photosynthesis as possible.
Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit.
Uses of glucose in plants
Used for respiration (both aerobic and anaerobic).
Converted into insoluble starch for storage in the stems, leaves and roots.
Used to produce fat or oil for storage (especially in seeds).
Used to produce cellulose, which strengthens the cell wall.
Combined with nitrate ions absorbed from the soil to produce amino acids for protein synthesis.
Practical 6 (rate of photosynthesis)
IV - Distance of the light from the pondweed
DV - Number of bubbles produced in 3 minutes
CV - Temperature, Volume of water
Procedure - Place a piece of pondweed into a beaker of water.
Use a light a set distance from the plant.
Record the number of bubbles observed in three minutes.
Repeat steps for different distances.
