What is the factor which is limiting the rate of photosynthesis at point x on the graph? light intensity commentary: in any question on limiting factors, the factor on the x axis remains a limiting factor limiting factor. Temperature, carbon dioxide concentration and light intensity can all be limiting factors on photosynthesis. for as long as the graph continues to rise in this case the point at which it levels off. At this point photosynthesis may still be limited by other factors such as temperature or carbon dioxide concentration. Absorption spectrum of chlorophyll the graph shows the absorption spectrum of chlorophyll a and the rate of photosynthesis over the same range of wavelengths. What evidence on the graph indicates that chlorophyll a is not the only pigment involved in photosynthesis? three factors can limit the speed of photosynthesis light intensity, carbon dioxide concentration and temperature. Light intensity without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide.

Carbon dioxide concentration sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. If you plot the rate of photosynthesis against the levels of these three limiting factors, you get graphs like the ones above. The leaves are the part of a plant where most photosynthesis takes place.

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if you cut a leaf in half and look at the cut end you will see something like this:

'stomata'

guard cells

osmosis

why do the swollen cells bend?

Photosynthesis is the way that plants make their food using energy from sunlight. what is the word equation for photosynthesis? plants use the green dye or pigment called chlorophyll to pick up the energy from the sunlight. Plants make sugar and use some of it for energy to keep them alive respiration but they also use some for growth and repair by making fats and proteins. However, it is not always sunny so plants need to be able to store some ofthe sugar they make, so they convert it to a storage carbohydrate. why bother storing it as starch? plants could use starch or glucose. starch is insoluble it does not dissolve in water while glucose is soluble. This means that if starch is used, less water is required to keep its food stored.

what things might effect how well plants can carry out photosynthesis? the amount of water is effected by how much is taken up through the roots and how much is lost from the leaves. If less water is available in the leaf then photosynthesis will occur more slowly. Similarly, if there is less carbon dioxide around then photosynthesis will occur more slowly. There wont be enough of the fuel substrate to get the reaction to work. Which usually means it is cooler too, then there is less energy for photosynthesis and it occurs more slowly.

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So photosynthesis works best when it is warm and sunny don't we all! how could you measure how quickly photosynthesis is occurring? you could wait ages and then see how much glucose is in the plant. Boring and slow! alternatively, one favourite way is to measure how much oxygen gas is given off. This can be done easiest by counting the bubbles of gas as they come off a water plant like the pondweed, elodea. When plants have their stoma open during the day, they can let carbon dioxide and oxygen diffuse through them. However, water can also diffuse out from the moist inside of the leaf to the drier air outside.

Transpiration is a bit like the sweat on our skin and may also help to cool the leaves. On a hot sunny day plants could become dehydrated as they lose water even though photosynthesis works best in these conditions. They cannot draw up water from their roots quickly enough so photosynthesis starts to slow down. A big problem! so how do plants stop themselves drying out? they close their stomata. A very neat trick! doc brown's science biology revision notes amp check out links at the end too suitable for gcse/igcse biology/science courses or their equivalent photosynthesis photosynthesis is summarised by the equation. carbon dioxide + water light energy/chlorophyll gt glucose + oxygen this is the process by which plants make food. For themselves, and for most animal life, including us too via food chains! the green chlorophyll is in structures called chloroplasts, so photosynthesis takes place in chloroplasts.

The carbon dioxide diffuses in through the stomata of the guard cells effectively pores that can open and close ie co₂ in, and oxygen o₂ out in the day and o₂ in at night. During photosynthesis light energy is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some plant cells and algae, this energy is used by converting carbon dioxide from the air and water from the soil into sugars e.g. Photosynthesis takes place in the leaves of all green plants and is the main function of leaves.

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So carbon dioxide diffuses into leaves, water comes up from the roots via the xylem tubes, oxygen diffuses out and sugars are transported around the plant by the phloem tubes. A a large surface area is provided by having broad leaves, beneath the apparently flat surface of a leaf is quite a porous layer of air spaces between the outer layers of cells particularly on the underside of leaves quite often the lower surface of a leaves feel rougher and 'roughness' means a more disrupted surface of a larger surface area. B containing green chlorophyll in chloroplasts to absorb light, that's why plants look so green, they contain a relatively high concentration of chlorophyll, c stomata for gas exchange carbon dioxide, oxygen and water vapour , stomata are tiny holes in the leaves which can open and close to let oxygen and carbon dioxide in and out both associated with photosynthesis and respiration and water vapour out transpiration.

I shortage of light usually sunlight slows photosynthesis since the greater the light intensity, the greater the rate of photosynthesis ii low temperature. Slows down the rate of photosynthesis a general rule for all chemical reactions a combination of both i and ii will cause very different rates between photosynthesis in winter much less, slower compared to summer much more, faster. I shortage of carbon dioxide will also slow down the rate of photosynthesis, so these are three factors affect the rate of photosynthesis see the three graphs below. light, temperature and the availability of carbon dioxide interact and in practice any one of them may be the factor that limits photosynthesis. You can relate the principle of limiting factors to the economics of enhancing the following conditions in greenhouses: light limitation light energy is needed for photosynthesis, so as the light intensity increases, the rate of photosynthesis chemical reactions steadily increases in a linear manner. However, eventually the rate levels off due to limitation of the carbon dioxide concentration or the temperature. Light intensity falls to zero at night and there is much less light in winter, so these place limits on photosynthesis.