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Photosynthesis is the process by which chlorophyll-containing organisms-green plants, algae, and some bacteria capture energy in the form of light and convert into chemical energy (Microsoft Encarta, 1995). The chlorophyll found in plants is essential to the process of photosynthesis, as it absorbs light energy. Once it captures light energy in the violet and red portions of the spectrum, it transforms it into chemical energy through a series of reactions (Microsoft Encarta, 1995).
The purpose of this lab was to determine what colour of light absorbed by plants produces a faster rate of photosynthesis. Three colours of light were used (blue, green, yellow) and were individually placed in an enclosed environment with a Grape Hyacinth Muscari plant for four hours. To determine which colour of light was best for photosynthesis, the plants were tested for starch content after the four hour time period was finished. The higher the starch level, the faster or more efficient rate of photosynthesis.
The blue light should produce the most efficient rate of photosynthesis as plants best absorb light with wavelengths of between 400 - 450 nanometres and 600 - 650 nanometres. Blue light is found between the wavelengths of 400 - 450 nanometres, therefore it should be the most efficient.
-3-100 watt light bulbs
-3 Grape Hyacinth Muscari plants
-blue, green, yellow cellophane light filters
-50ml distilled water
1. Place each of the Grape Hyacinth plants into individual pots. Water each plant.
2. Test for starch- take a sample of the plant's leaf from one of the plants
-boil 50ml of distilled water and place the leaf in it, boil the leaf for 4 minutes
-after the 4 minutes the leaf will appear limp, dark, smell cooked
-boil 50ml of alcohol at a lower temperature (make sure to wear safety goggles)
-place the leaf sample in the alcohol and boil for 4 minutes
-remove the leaf from the alcohol and place in a petri dish
-place 3-5 drops of iodine on the leaf and record results
3. Use a 60 watt light bulb and cover the lamp with a piece of blue cellophane filter
4. Fill two 500ml beakers with cool water.
5. Place one of the plants in a cupboard and the two beakers filled with water in front of it.
6. Clamp the light to the inside of the cupboard, in front of the beakers and the plant.
7. Turn on the light and leave the plant in the cupboard for four hours.
8. After the four hours are up, take a sample of the leaf and test it for starch (use the above steps).
9. Repeat the above steps for each plant and different light used. Take a starch test for each plant after it has been placed in the light.
The first Grape Hyacinth plant which was placed under blue light turned a dark brownish red colour, when it was tested with the iodine after the four hours. The leaf also contained some darker spots on it. The plant placed under the green light was not as dark in colour and contained fewer dark spots. The leaf of the third plant which was placed in the yellow light turned a light brownish red colour and contained one or two dark spots.
COLOUR OF LIGHT EXPOSED TO PLANTS STARCH TEST RESULTS
Blue Dark Brownish Red, Many Dark Spots (Starch present)
Green Light Brownish Red, Fewer Dark Spots(Some Starch present)
Yellow Lighter Brownish Red Colour, Few Dark Spots(Starch Present)
The results concur with the hypothesis as the blue light produced the higher rate of photosynthesis due to the higher amount of starch present in the Hyacinth leaf. The green light produced the second highest amount of starch indicated by it's lighter colour and it's fewer dark spots than the blue light's results. The yellow light produced the lowest output of starch, therefore, it produced the slowest rate of photosynthesis.
Optimum wavelengths of light absorbed by the plants for photosynthesis can be found between 400 - 450 nanometres and between 600 - 650 nanometres (Raven & Johnson,1995). This explains why the blue light produced a higher rate of photosynthesis, because it falls between the wavelengths of 400 - 450 nanometres. The green light produced the second highest amount of starch, although it shouldn't have. The chlorophyll molecule tends to absorb red and blue light strongly while it absorbs
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Plant physiology, Photosynthesis, Agronomy, Excipients, Printing, Starch, Chlorophyll, Leaf
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