Factors affecting photosynthesis
There are several ways of measuring the rate of photosynthesis 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 respiring, 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 in lighting conditions unfavourable for photosynthesis 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 If a substance is denatured, its structure and function is altered. This can be caused by heat, altered pH or by chemical agents..
Chlorophyll
Chlorophyll absorbs the light energy required to convert carbon dioxide and water into glucose.
Chlorophyll is green - so absorbs the red and blue parts of the Range of all possible frequencies of radiation, eg ultraviolet light is part of the EM spectrum. and reflects the green part of the spectrum.
Leaves with more chlorophyll are better able to absorb the light required for 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 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. 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.