The granum (plural grana) is a stack of which contains the photosynthetic pigments; this is where the light dependent stage takes place:
Our results are contradictory with our hypothesis, based on our statistical results. There were several problems with our experiment that could have been taken into consideration. First, when taking respiration rates the foil wasnt covering the chamber all the way letting some external light in. Second, the colored cellophane only allows approximately 70% of light through; this might have prevented the plant from absorbing the amount of light energy needed to have a significant photosynthetic rate. Third, the fast paced moving between trials lost time and efficiency. By having short trials (2.5 min.) we might not have allowed the plant enough time to adjust its photosynthetic rate to the different wavelengths of light energy. Plus by moving the plant, and switching from cellophane to foil (or vise versa), might have screwed up the photosynthetic cycle by exposing it to white light.
The light-independant reactions of photosynthesis occur in the stroma of the chloroplast and involve the conversion of carbon dioxide and other compounds into glucose. The light-independent reactions can be split into three stages, these are carbon fixation, the reduction reactions and finally the regeneration of ribulose bisphosphate. Collectively these stages are known as the Calvin Cycle.
Green plant have six closely related photosynthesis pigments(in order of increasing polarity): Carotene (orange pigment),XanthophyII (yellow pigment), Phaeophytin
(yellow-brown pigment), ChlorophyII
(blue-green pigment) and ChorophyII
The retention factor (R
may be defined as the ratio of the distance traveled by the substance to the distance traveled by the solvent
3.1 MATERIAL AND APPARATUS
3.2 ARRANGEMENT OF APPARATUS
How to identify the presence of difference pigments in chlorophyll's
What are the factors affecting these R
USING PAPER CHROMATOGRAPHY
80% of Acetone
"Cekur Manis" or Red Spinach Leaves
Mortar and Pestle
Muslin (cheese cloth)
Boiling Tube/Large Test Tube With Stopper (24x150mm)
Solvent ( 1 Part 80% Acetone and 9 Part Petroleum Ether)
Whatman no.1 Chromatography Paper Strip (20 X 130mm)
Dark Paper/Black Sugar Paper
Retort Sand/ Test Tube Rack
Diagram 1: Assembling of chromatography apparatus
Photophosphorylation is the production of ATP using the energy of sunlight. Photophosphorylation is made possible as a result of chemiosmosis. Chemiosmosis is the movement of ions across a selectively permeable membrane, down their concentration gradient. During photosynthesis, light is absorbed by chlorophyll molecules. Electrons within these molecules are then raised to a higher energy state. These electrons then travel through Photosystem II, a chain of electron carriers and Photosystem I. As the electrons travel through the chain of electron carriers, they release energy. This energy is used to pump hydrogen ions across the thylakoid membrane and into the space within the thylakoid. A concentration gradient of hydrogen ions forms within this space. These then move back across the thylakoid membrane, down their concentration gradient through ATP synthase. ATP synthase uses the energy released from the movement of hydrogen ions down their concentration gradient to synthesise ATP from ADP and inorganic phosphate.
An absorption spectrum is a graph showing the percentage of light absorbed by pigments within the chloroplast, for each wavelength of light. An example is the absorption spectrum of chlorophyll a and b. The best absorption is seen with violet-blue light. There is also good absorption with red-orange light. However most of the green-yellow light is reflected and therefore not absorbed. This wavelength of light shows the least absorption.
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).
Considering that not all light energy is used for photosynthesis we propose an alternative hypothesis. In a previous experiment the pigment xanthophylls absorbed significant amounts of blue light. In new research it is found that this pigment could be an important component in a process called energy dissipation rather than photosynthesis. In order to not overwhelm the plant with photosynthesis and respiration, this photon energy goes to other functions or formations of the plant. Further research on the function of xanthophylls will need to be conducted in order to understand the processes of plant function.
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.
Photosynthesis occurs inside chloroplasts. Chloroplasts contain chlorophyll, a green pigment found inside the thylakoid membranes. These chlorophyll molecules are arranged in groups called photosystems. There are two types of photosystems, Photosystem II and Photosystem I. When a chlorophyll molecule absorbs light, the energy from this light raises an electron within the chlorophyll molecule to a higher energy state. The chlorophyll molecule is then said to be photoactivated. Excited electron anywhere within the photosystem are then passed on from one chlorophyll molecule to the next until they reach a special chlorophyll molecule at the reaction centre of the photosystem. This special chlorophyll molecule then passes on the excited electron to a chain of electron carriers.
So how can these factors have an effect on the rate of photosynthesis? Lets start off with the light intensity. When the light intensity is poor, there is a shortage of ATP and NADPH, as these are products from the light dependent reactions. Without these products the light independent reactions can't occur as glycerate 3-phosphate cannot be reduced. Therefore a shortage of these products will limit the rate of photosynthesis. When the carbon dioxide concentration is low, the amount of glycerate 3-phosphate produced is limited as carbon dioxide is needed for its production and therefore the rate of photosynthesis is affected. Finally, many enzymes are involved during the process of photosynthesis. At low temperatures these enzymes work slower. At high temperatures the enzymes no longer work effectively. This affects the rate of the reactions in the Calvin cycle and therefore the rate of photosynthesis will be affected.
To test this we used about 5 grams of leaves for each trial, and placed them in a gas chamber. On two sides of the gas chamber we placed two clear containers filled with water to serve as the temperature regulators. Behind the water containers we placed lights directed at the plant. We ran three trails for each different leaf we used. Each trail consisted of measuring the amount of CO2, with a CO2 gas sensor under blue light, red light, and green light. We made sure to switch the order of colors in each trail as an experimental control, to minimize error. Since we know that photosynthesis requires CO2, and we know that blue light pigments absorb the most light energy, we predicted that under blue light the most CO2 would be used.