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Photosynthesis - absorbance lab

Page history last edited by Charles Forstbauer 14 years, 4 months ago

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Totaled 11/06 Mr F

Totaled 11/03 Mr F

 

The amount of light absorbed by the pigment,chlorophyll, at different wavelengths of light uis measured my a spectrometer

 

http://led-lighting-systems.com/images/absorbance-wavelength.jpg

As this spectrometer shows, violets and blue are absorbed the best by the chlorophyll. Because these colors are absorbed the best, it means that they are likely to be visible the least. The green to orange colors are most reflected by the chlorophyll, and their pigments will be much more visible. In the fall however, when the chlorophyll is not working, the red pigments will start to be reflected more and absorbed less, making the leaves turn more red and orange than before.

 

The extent to which a sample absorbs light depends strongly upon the wavelength of light. For this reason, spectrophotometry is performed using monochromatic light. Monochromatic light is light in which all photons have the same wavelength.

In analyzing a new sample, a chemist first determines the sample's absorbance spectrum. The absorbance spectrum shows how the absorbance of light depends upon the wavelength of the light. The spectrum itself is a plot of absorbance vs wavelength and is characterized by the wavelength (λmax) at which the absorbance is the greatest.

 

chlorophyll and white light interact to produce green color because chlorophyll absobs every color but green.  Since green is not absorbed, it is reflected-giving the plant its green color.

 

Well you are spot on about it being chlorophyll inside the chloroplasts that gives a plant the green colour. There are other pigments in the leaves too, such as xanthophylls (yellows) and carotenoids (yellows, oranges and reds). These pigments are also used in photosynthesis but occur in lesser quantities than the green chlorophyll. The combinations of the different pigments make different shades of green.

Now the reason that plants look green is that they are trying to obtain energy from the sun using a particular part of the light spectrum, mainly the red and infra red wavelengths. If you remember from your physics classes the colour you see is the colour that is reflected from the object, the other colours are absorbed. So in the case of green plants, the green wavelength is reflected and all the other colours, especially reds and blues, are absorbed to drive the energy cycle in the plants.

Chlorophyll does best in the red (around 670 nm) and blue (around 500 nm) areas of the spectrum. That's why many plants have the additional pigments (xanthophylls and carotenoids) called accessory pigments that feed light energy to chlorophyll "a" from light. Chlorophyll is almost useless in the green part of the spectrum, and doesn't absorb that colour. That is why most plants are green.

Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Chlorophyll absorbs light most strongly in the blue and red but poorly in the green portions of the electromagnetic spectrum, hence the green colour of chlorophyll-containing tissues such as plant leaves.

Chlorophyll molecules are specifically arranged in and around pigment protein complexes called photosystems which are embedded in the thylakoid membranes of chloroplasts.The function of the vast majority of chlorophyll (up to several hundred molecules per photosystem) is to absorb light and transfer that light energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems. Because of chlorophyll’s selectivity regarding the wavelength of light it absorbs, areas of a leaf containing the molecule will appear green.

 

http://t1.gstatic.com/images?q=tbn:9AblE3FuM4NS-M:http://3.bp.blogspot.com/_6Am7CgmLuZE/SYqBY83HkvI/AAAAAAAAALM/xhsgJZPoWZc/s400/chlorophyll+graph.jpg As you can see in this spectrometer sample, in the green zone, the line drops DRAMATICALLY. this means that the green color is not being absorbed by the chlorophyll like all the rest of the colors.  Meaning that the plant is ABSORBING all of the other colors EXCEPT for green.  Green is being REFLECTED. the color that is reflected is the                                                                   color that it appears.  Therefore, most plants are green because their chlorophyll reflects green.

 

~During the summer the trees are producing lots of cholorophyll, which masks the other pigments in the leaves. However as the days start to become shorter in the Fall the production of chorlorphyll decreases and eventually stops. This allows the other colors that were once hidden by the chlorophyll to show, therefore creating the beautiful reds, yellows, and oranges, that we see in the Fall.

~Another example of this is bananas. When bananas are green when they are unripe because the plant is producing a lot of chlorophyll. However has the banana starts to ripen the chlorophyll breakes down and disappears revealing the yellow color which has been there all along.

 

How leaves change color

This picture shows the cross section of a leaf, however it is different from ones that we have seen because it shows the color changes.

 

 

 

          This lab was done to show the pigments of leaves.  The 4 pigments are clear and visible on the paper.  They are spread out from green, to a lighter orange, to yellow, and than a clear yellow line at the top.  This shows the change over time of leaves.  Different pigments last longer, therefore changing the colors of the leaves.  The paper has different peaks with the four pigments.  That is what the lab does, it shows the four pigments.

 

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