Factors affecting photosynthesis
There are several ways of measuring the rate of A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. in the lab. These include:
- the rate of Gaseous element making up about 20% of the air, which is needed by living organisms for respiration. output
- the rate of A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis. uptake
- the rate of Food belonging to the food group consisting of sugars, starch and cellulose. Carbohydrates are vital for energy in humans and are stored as fat if eaten in excess. In plants, carbohydrates are important for photosynthesis. production
These are not perfect methods as the plant will also be The chemical change that takes place inside living cells, which uses glucose and oxygen to release the energy that organisms need to live. Carbon dioxide is a by-product of respiration., which will use up some oxygen and carbohydrate and increase carbon dioxide output.
Several factors can affect the rate of photosynthesis:
- light intensity
- carbon dioxide concentration
- temperature
The amount of The green chemical inside the chloroplasts of plant cells. It enables photosynthesis to take place. also affects the rate of photosynthesis:
- plants growing in darker areas synthesise more chlorophyll, to absorb the light required
- the effects of some plant diseases affect the amount of chlorophyll, and therefore the ability of a plant to photosynthesise
Light intensity
Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide and a suitable temperature.
Increasing the light intensity increases the rate of photosynthesis, until some other factor - a A factor which, if in short supply limits or reduces the rate of photosynthesis, eg temperature, light intensity and carbon dioxide concentration. – becomes in short supply.
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At very high light intensities, photosynthesis is slowed and then inhibited, but these light intensities do not occur in nature.
Carbon dioxide concentration
Carbon dioxide - with water - is one of the reactants in photosynthesis.
If the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase.
Again, at some point, a factor may become limiting.
Temperature
The chemical reactions that combine carbon dioxide and water to produce glucose are controlled by A protein which catalyses or speeds up a chemical reaction.. As with any other enzyme-controlled reaction, the rate of photosynthesis is affected by temperature.
At low temperatures, the rate of photosynthesis is limited by the number of molecular collisions between enzymes and substrates. At high temperatures, enzymes are The change in the shape of a protein such as an enzyme that results in them no longer fitting their substrate..
Chlorophyll
The green chemical inside the chloroplasts of plant cells. It enables photosynthesis to take place. is the green A coloured chemical. found in Contains the green pigment chlorophyll; the site of photosynthesis. which absorbs light energy for photosynthesis.
Leaves that are growing in darker conditions usually have more chlorophyll. They receive less light so they require more chlorophyll to increase their rate of photosynthesis.
The compensation point
These graphs have been plotted with rate of photosynthesis against the factor under investigation.
If oxygen production or carbon dioxide uptake is used as a measure of photosynthetic rate, the graphs are slightly different. The line does not go through the origin.
This is because oxygen production and carbon dioxide uptake are affected by respiration as well as photosynthesis. For instance, if a graph is plotted of carbon dioxide against light intensity:
The compensation point is the light intensity at which the rate of photosynthesis is equal to the rate of respiration.
A similar graph will be obtained if oxygen production is plotted against light intensity.
