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Photosynthesis - definition of photosynthesis by The …

It is the combination of pigments in a plant which determines which wavelengths of light can be utilised in photosynthesis.

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sunlight is absorbed by chlorophyll in a leaf B


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We can see how different wavelengths of light affect photosynthesis by
looking at action spectra.

The rate of absorption in photosynthesis can be affected by the different wavelengths of light

As we can see, there is a close relationship between the action spectrum and absorption spectrum of photosynthesis. There are many different types of photosynthetic pigments which will absorb light best at different wavelengths. However the most abundant photosynthetic pigment in plants is chlorophyll and therefore the rate of photosynthesis will be the greatest at wavelengths of light best absorbed by chlorophyll (400nm-525nm corresponding to violet-blue light). Very little light is absorbed by chlorophyll at wavelengths of light between 525nm and 625 (green-yellow light) so the rate of photosynthesis will be the least within this range. However, there are other pigments that are able to absorb green-yellow light such as carotene. Even though these are present in small amounts they allow a low rate of photosynthesis to occur at wavelengths of light that chlorophyll cannot absorb.

carbon dioxide is taken in from the air C

The action spectrum of photosynthesis is a graph showing the rate of photosynthesis for each wavelength of light. The rate of photosynthesis will not be the same for every wavelength of light. The rate of photosynthesis is the least with green-yellow light (525 nm-625 nm). Red-orange light (625nm-700nm) shows a good rate of photosynthesis however the best rate of photosynthesis is seen with violet-blue light (400nm-525nm).

Red (610 - 700 nm) and blue (450 - 500 nm) wavelengths are most effective in promoting photosynthesis. Green (500 - 570 nm) light is least effective - it is not absorbed by plants but is reflected which is why green plants appear to be green. The conclusion: different wavelengths of light affect the photosynthetic process. Red and blue light support the highest rates of photosynthesis (although white light causes the most disks to float, remember that white is all wavelengths so it can be expected to result in the highest percentage).

water is transported from the roots D

Wavelength (nm)

Colour of light













In photosynthetic plants the pigments are very important.

You can relate these results to Exercise A, Part 3. Remember how it was shown that wavelengths of red (610 - 700 nm) and blue (450 - 500 nm) resulted in the greatest amount of photosynthesis? The same is shown here in the graph - light is absorbed by the pigments better at those wavelengths as compared to others. Green, once again, is absorbed least. It ain't easy being green. ;-)

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    photosynthesis A

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This is because plants also have different pigments

Plants utilize the process of photosynthesis to convert solar energy into chemical energy to produce cellular respiration. The process of photosynthesis uses the energy of sunlight, which is then absorbed into different pigment types to help the cyclical functions that eventually create atmospheric oxygen. In this experiment we asked how different colors of light effect the rate of photosynthesis. The experiment attempted to see how blue colored and red colored lights affected the rate of photosynthesis. It was hypothesized that because plants absorb more red light, then we predict plants in red light should have a higher rate of photosynthesis when compared to plants in blue. The hypothesis was tested by taking the leaves of a live plant and placing the leaves in a flask. A carbon dioxide gas probe was then placed in the flask to test if the levels of carbon dioxide changed. The independent variable was the color of light and the dependent variable was the rate of photosynthesis in change in levels of carbon dioxide per minute per gram. The change in carbon dioxide levels were proportional to the rate of photosynthesis. Thus red light and blue light was placed upon the flasks of leaves for a total of thirty minutes. The first and last ten minutes the leaves were set in the light and the second ten- minute increment the leaves were in the dark. The second ten minutes was to see if carbon dioxide levels decreased thus to control the cellular respiration. The results show in comparing the carbon dioxide levels that the p=value is .36 meaning there was no significance in the comparison. Therefore the different wavelengths in light made no extreme difference on the rate of photosynthesis. In comparison to other experiments done by others the results were much the same finding that neither light wavelength affected the rate of photosynthesis. The experiment was done with a limited amount of time and the leaves were most likely dead by the end of the experiment. A better hypothesis would be to see how the wavelengths of different colored lights like yellow and green affect the rate of photosynthesis. The use of more live plants would help obtain better results also.

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