2. By Mary Reyes Lauren Dobry & Haleigh Rousseau

3. Basic Information Photosynthesis involves the conversion of : light energy chemical energy Light from the sun is composed of a range of wavelengths (colors). Chlorophyll is the main photosynthetic pigment. Light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen. ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules. Generally, cell respiration is a catabolic process whilst photosynthesis is an anabolic one

4. Absorption of RED, BLUE, and GREEN Light by Chlorophyll When a plant leaf is hit by sunlight, the BLUE and RED wavelengths of light are absorbed by chlorophyll and used for photosynthesis. However, almost all the energy of the GREEN wavelengths is reflected and not absorbed. Therefore, photosynthesis cannot occur when the leaf is hit solely by a green wavelength.

5. A chart showing the Action and Absorption Spectrums. BLUE, VIOLET, and RED light are most effective during the process of photosynthesis, since chlorophyll is the predominant photosynthetic pigment. Notice the similarities between the Action and Absorption Spectrums. The most absorbed wavelengths are the most active during photosynthesis, while the most reflected wavelengths are the least active.

6. Effect of changing light intensity There is a positive correlation between light intensity and photosynthesis until the enzymes and other factors are already working at their maximum rate. When this occurs, the rate of photosynthesis plateaus.

7. Effect of changing temperature As the temperature increases, the rate of photosynthesis and the incidence of molecular collisions also increases. However, at a certain temperature, the enzymes and other proteins become denatured and the rate of photosynthesis drops tremendously until it becomes non-existent.

8. Effect of changing CO² concentration There is a positive correlation between carbon dioxide concentration and photosynthesis, but the rate of reaction reaches a plateau unless light or temperature is also increased. Aquatic plants can alter the pH of the water during photosynthesis, raising it, due to CO² absorption.

10. Structure of the Chloroplast Unlike respiration, where some of the steps occur outside of the mitochondrion, all of the photosynthetic process occurs within the chloroplast. The chloroplast contains a double membrane and is about the same size as a bacterial cell. Like the mitochondrion, it contains its own DNA and 70S ribosomes. The DNA of the chloroplast is in the form of a ring. Besides DNA and ribosomes, the interior of the chloroplasts includes the grana, thylakoids, and stroma.

11. A granum is made up of numerous thylakoids stacked like a pile of coins. The thylakoids are flattened membrane sacs with components necessary for the absorption of light, which is the first step in the process of photosynthesis. The fluid stroma is similar to the cytosol of the cell. It occurs outside the grana but within the double membrane. Stroma contains many enzymes and chemicals necessary to complete the process of photosynthesis. Like mitochondria, chloroplasts are capable of reproducing independently of the cell.

12. Chloroplast StructureFunction Allowed Extensive membrane surface area of the thylakoids Allows greater absorption of light by photosystems Small space (lumen) within the thylakoids Allows faster accumulation of protons to create a concentration gradient Stroma region similar to the cytosol of the cell Allows an area for the enzymes necessary for the Calvin cycle to work Double membrane on the outside Isolates the working parts and enzymes of the chloroplast from the surrounding cytosol

14. The First Stage of Photosynthesis This stage is a set of reactions typically referred to as the light-dependent reactions. During this stage, chlorophyll (and other photosynthetic pigments) absorb light energy and convert it into a form of chemical energy, specifically ATP. Light energy is also used to accomplish a reaction called photolysis, during which a water molecule is split into its component elements: hydrogen and oxygen.

15. The oxygen that is split away due to the photolysis of water is typically released from the plant as a waste product. Here is an animation that explains the specifics of the light-dependent reactions: http://www.youtube.com/watch?v=eY1ReqiYwYs http://www.youtube.com/watch?v=eY1ReqiYwYs

16. Respiration Chemiosmosis Photosynthesis Chemiosmosis Electron Transport Chain in membranes of cristae Electron Transport Chain in membranes of thylakoids Energy released when electrons are exchanged from one carrier to another Released energy used to actively pump hydrogen ions to intermembrane space Released energy used to actively pump hydrogen ions to thylakoid space Hydrogen ions come from matrixHydrogen ions come from stroma Hydrogen ions diffuse back into matrix through channels of ATP synthase Hydrogen ions diffuse back into stroma through channels of ATP synthase ATP synthase catalyses the oxidative phosphorylation of ADP to ATP ATP synthase catalyses the phosphorylation of ADP to ATP

17. The Second Stage of Photosynthesis

18. The second stage is a series of reactions collectively known as the light-independent reactions or the Calvin Cycle. ATP and hydrogen are used as forms of chemical energy to convert carbon dioxide and water into useful organic molecules for the plant. Carbon dioxide is one of the few molecular forms of carbon that is considered to be inorganic. Glucose, a typical product of photosynthesis, is an organic molecule. It requires six inorganic carbon dioxide molecules to form one glucose molecule.

19. This conversion of an inorganic form of an element to an organic form is known as fixation. Therefore, photosynthesis can be described as a series of reactions in which carbon dioxide and water are fixed into glucose, and oxygen is produced as a by-product. Fixation requires energy that comes directly from the ATP and hydrogen created in the first stage of photosynthesis. Ultimately, the energy can be traced back to sunlight.

20. It is also important to note that glucose is only one of the many possible organic molecules that can form from photosynthesis. Here is an animation that explains the specifics of the Calvin Cycle: http://www.youtube.com/watch?v=mHU27qYJNU0& NR=1 http://www.youtube.com/watch?v=mHU27qYJNU0& NR=1

21. Light-dependent Reaction Light-independent Reaction Occurs in the thylakoidsOccurs in the stroma Uses light energy to form ATP and NADPH Uses ATP and NADPH to form triose phosphate Splits water in photolysis to provide replacement electrons and H⁺, and to release oxygen to the atmosphere Returns ADP, inorganic phosphate and NADP to the light-dependent reaction Includes two electron transport chains and photosystems I and II Involves the Calvin cycle

23. This is an alternate way creating ATP during the light-dependent reaction. It only occurs when light is not the limiting factor of photosynthesis, and when there are large amounts of NADPH in the chloroplasts. Light energized electrons from photosystemI go to the cytochrome complex and finish the last leg of the electron transport train. ATP is then created via chemiosmosis NADPH is not created because the electrons do not go through the second electron transport chain

25. Which two colors of light does chlorophyll absorb most? A. Red & Yellow B. Green & Blue C. Red & Green D. Red & Blue

26. The answer was D D

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28. How is the proton gradient generated in chloroplasts during photosynthesis? A. flow of electrons from carrier to carrier in the thylakoid membrane causes pumping of protons across thylakoid membrane B. light causes protons to flow through protein channels in the thylakoid membrane C. light splits water molecules in the stroma causing the release of protons D. protons are pumping across the thylakoid membrane using energy from ATP

29. The answer was A A

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31. Plants living in water can cause a pH change in the water when they carry out photosynthesis. What is the pH change and what causes it? A. pH falls because oxygen is released B. pH rises because carbon dioxide is absorbed C. pH falls because carbon dioxide is absorbed D. pH rises because oxygen is released

32. The answer was B B

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34. Why is the action spectrum for photosynthesis similar to the absorption of photosynthetic pigments? A. Photosynthetic pigments have the same optimum temperature as enzymes used in photosynthesis B. Plants absorb the same photosynthetic pigments for use in photosynthesis C. Only wavelengths of light absorbed by pigments can be in photosynthesis D. Amount of energy absorbed by photosynthetic pigments is equal to activation energyfor photosynthesis

35. The answer was C C

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37. What is the advantage of having a small volume inside the thylakoids of the chloroplast? A. high proton concentration is rapidly developed B. high electron concentration is rapidly developed C. photosynthetic pigments are highly concentrated D. enzymes of the Calvin cycle are highly concentrated

38. The answer was A A

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40. Which diagram represents the process of cyclic photophosphorylation? A.B. C.D.

41. The answer was B B

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43. Which graph shows the effect of increasing carbon dioxide concentration on the rate of photosynthesis? A.B. C.D.

44. The answer was B B

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46. Which line shows an action spectrum of photosynthesis? A.B. C.D.

47. The answer was A A

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49. What is occurring at X during the light-dependent reaction in photosynthesis? A. ADP + phosphate ATP B. NADP⁺ NADPH + H⁺ C. H₂O O²⁻ + 2H⁺ D. NADPH + H⁺ NADP⁺

50. The answer was A A

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