NAME: Option Group. Photosynthesis. Workbook

Transcription

1 NAME: Option Group Photosynthesis Workbook

2 REVISION CHECKLIST AND ASSESSMENT OBJECTIVES Instructions Regular revision throughout the year is essential. It s vital you keep a track of what you understand and what you don t understand. This booklet is designed to help you do this. Use the following key to note how well you understand the work after your revision. Put the letter R, A or G in the table. If you place an R or an A then you should make a note of what you are struggling with and the end of this book under the relevant section and seek help with this. Key R = Red. I am not confident about my knowledge and understanding A = Amber. I am fairly confident about my knowledge and understanding G = green. I am very confident about my knowledge and understanding AO1 Demonstrate knowledge and understanding of scientific ideas, processes, techniques and procedures. AO2 Apply knowledge and understanding of scientific ideas, processes, techniques and procedures: In a theoretical context In a practical context When handling qualitative data Tyrone John, Chartered Biologist 2

3 When handling quantitative data AO3 Analyse, interpret and evaluate scientific information, ideas and evidence, including in relation to issues, to: Make judgments and reach conclusions Develop and refine practical design and procedures The ability to select, organise and communicate information and ideas coherently using appropriate scientific conventions and vocabulary will be tested across the AO. Tyrone John, Chartered Biologist 3

4 The following points are what you need to know, revise and answer questions on. Photosynthesis Light dependent reactions 1. Can you draw and label a chloroplast 2. Can you identify the structures in a chloroplast were the light dependent reactions occur. 3. Can you name at least 4 photosynthetic pigments. 4. Can you draw and label a light harvesting complex (photosystem). 5. Can you explain the function of accessory pigments. 6. Can you define an action spectrum. 7. Can you define an absorption spectrum. 8. Can you distinguish between absorption and reflection. 9. Can you fully describe the process of cyclic and non-cyclic photophosphorylation. 10. Can you describe the function of: high energy electrons, electron acceptors, electron carriers, the photolysis of water, protons, a proton gradient, ATP synthetase, PSI, PSII. 11. Can you state the origin of the electrons in PSII 12. Can you state the origin of the electrons in PSI. 13. Can you describe how a proton gradient is created. Light independent reactions (Calvin Cycle) 14. Can you name all the intermediate molecules in the Calvin cycle. 15. Can you placed the intermediate molecules in the Calvin cycle in the correct order. 16. Can you place the products of the light dependent stage in the correct positions in the Calvin cycle. 17. Do you know the function of RUBISCO. 18. Can you state the function of triose phosphate. 19. Can you describe in words the formation of triose phosphate. Place an R, A or G when you have revised and make notes of what you do not understand in the relevant section at the back of this booklet. Tyrone John, Chartered Biologist 4

5 20. Can you describe in words the formation of the unstable 6C compound 21. Can you describe in words the formation of Ribulosebisphosphate. 22. Can you state where the Calvin cycle occurs. 23. Can you interpret graphical results of the Calvin cycle. Limiting Factors 24. Can you state the law of rate limiting factors. 25. Can you list the factors that limit the rate of photosynthesis. 26. Can you interpret graphs showing rate limiting factors. Prac 27. Can you calculate the Rf value from a thin layer chromatography experiment. 28. Can you describe and interpret results of experiments involving factors that affect the rate of photosynthesis. 29. Can you interpret and explain the results of the Calvin experiment using 2D chromatography 30. Can you interpret and explain the results of Theodor Engelmann experiments. Application of knowledge 31. Can you apply your knowledge of photosynthesis to unfamiliar scenarios? Tyrone John, Chartered Biologist 5

6 WORD BANK Below is a list of some key words and phrases you will need to learn and understand in this carbohydrate and general chemistry section nm nm. 3. Absorption spectrum. 4. Accessory pigment. 5. Action spectrum. 6. ADP. 7. Antennae complex. 8. ATP synthetase. 9. ATP. 10. Carotenoids. 11. Chlorophyll a. 12. Chlorophyll b. 13. Cyclic photophosphorylation. 14. Electron acceptors. 15. Electron carriers. 16. Electrons excited to a higher energy level. 17. Glycerate phosphate. 18. Granum. 19. High energy electrons 20. Increase the range of wavelengths absorbed so increase the efficiency of photosynthesis. 21. Light dependant stage/reactions. 22. Light harvesting unit. 23. Light independent stage/reactions, dark reactions, Calvin cycle. 24. NADPH 2, reduced NADP. 25. Non-cyclic photophosphorylation. 26. Oxygen. 27. Photolysis of water. 28. Photosystem I. 29. Photosystem II. 30. Photosystem. 31. Primary pigment. 32. Proton gradient. 33. Reaction centre. 34. Reduction. 35. Ribulose bisphosphate. 36. Ribulose phosphate. 37. Thylakoid membrane. 38. Triose phosphate. 39. Water. 40. Xanthophyll. 41. β carotene. Tyrone John, Chartered Biologist 6

7 GENERAL INTRODUCTION TO PHOTOSYNTHESIS Lesson preparation exercises Instructions Go to and Watch the video(s) and complete the following tasks. Completion date: 1. Make summary notes from the video(s) using the cornell template. Ensure you make an organised list of all the new terminology. Go to to learn how to use the cornell note taking method. Tyrone John, Chartered Biologist 7

8 ACTION AND ABSORPTION SPECTRA Lesson preparation exercises Instructions Go to and watch the video(s) and complete the following tasks. Completion date: 1. Make some summary notes from the video(s) using the cornell grid. 2. Thinking about and organising the new information from the video(s). i. State the location of the accessory pigments. ii. What happen to the rate of photosynthesis when light is reflected? iii. Explain the function of the accessory pigments. iv Approximately what wavelength of light is absorbed by Chlorophyll a and carotenoids. v What role did Theodor Englemann have is photosynthesis research? Tyrone John, Chartered Biologist 8

9 3. In seaweeds that are found on the shores around Britain, photosynthesis occurs during the time that they are submerged at high tide. Seaweeds found near the top of the shore are submerged for shorts periods in shallow water. Seaweeds found lower down the shore are submerged for longer periods in deeper water. As the light penetrates deeper water, red, orange and yellow wavelengths are absorbed by the seaweed, whereas in shallow water most wavelengths penetrate. The table below shows the relative rates of photosynthesis in a green seaweed, Ulva lactuca, and a red seaweed, Schizymenia dubyi, at different wavelengths of light. The relative rates of photosynthesis are compared to the rate in light with a wavelength of 660nm. Seaweed Rate of photosynthesis/arbitrary units 430 nm 540 nm 660 nm Ulva lactuca Schizymenia dubyi (i) Using the data in the table, suggest where each of these two seaweeds is most likely to be found on the seashore. Place a tick in the most appropriate box in each column. (2) Position on shore Ulva lactuca Schizymenia dubyi Top of the shore Middle of the shore Lower down the shore All regions (ii) Give a reasons for your answers. (4) Tyrone John, Chartered Biologist 9

10 4. Consider the diagram below which shows the results of an experiment: Fully explain the results. [5] Tyrone John, Chartered Biologist 10

11 Lesson preparation exercises Instructions LIGHT DEPENDENT REACTIONS Go to and watch the video(s) and complete the following tasks. Completion date: 1. Make some summary notes from the video(s) using the cornell grid. 2. Thinking about and organising the new information from the video(s). i. Tabulate the important terms about the light dependent stage below: Tyrone John, Chartered Biologist 11

12 ii. Complete for crossword below: Tyrone John, Chartered Biologist 12

13 iii. The diagram below shows the double membrane envelope of a chloroplast. Complete the diagram to show the structures involved in the light dependent reactions of photosynthesis. Label these structures. iv The table below shows 4 statements taken form a student s essay about the light dependent reactions of photosynthesis. Complete the table by placing a tick in the correct column next to each statement to show whether it is true or false. Statement True False Electrons in chlorophyll a are excited as light energy is absorbed. The energy absorbed by chlorophyll a is used to generate ADP and NADP ATP synthetase is located in the stroma Chlorophyll b is an accessory pigment Tyrone John, Chartered Biologist 13

14 LIGHT INDEPENDENT REACTIONS (CALVIN CYCLE) Lesson preparation exercises Instructions Go to and watch the video(s) and complete the following tasks. Completion date: 1. Make some summary notes from the video(s). 2. Thinking about and organising the new information from the video(s). i. Name the reaction catalysed by RUBISCO. ii Where does the Calvin cycle occur. iii State the functions of NADPH 2 and ATP. Tyrone John, Chartered Biologist 14

15 iv As one CO 2 molecule enters the Calvin cycle how many of the following molecules are used or produced: ATP NADPH 2 GP TP RuBP Rup v For the Calvin cycle to occur it requires 3 molecules of CO 2. Also 1 molecule of TP leaves the Calvin cycle to be used to make other compounds needed by the plant. Using this information, draw out the Calvin cycle with the following information clearly stated: The names of all intermediates placed in the correct sequence. The correct number of carbons for each intermediate. The correct number of each intermediate The correct number and position of NADPH 2, NADPH, ATP, ADP Tyrone John, Chartered Biologist 15

16 Space for Calvin cycle Tyrone John, Chartered Biologist 16

17 PRACTICAL PHOTOSYNTHESIS Practical No 1 Chromatography of photosynthetic pigments Chromatography is a technique that can separate the individual components of a mixture. There are different types of chromatography, but the one that is used here is called thin layer chromatography very similar to paper chromatography. The many different types of light absorbing pigments found in the leaf of plants make up a mixture that thin layer chromatography can separate. Because the pigments are coloured, their separation can be viewed with the unaided eye, as shown below: Tyrone John, Chartered Biologist 17

18 The pigments can be identified by calculating the retention factor (R f index): Rf = Distance moved from the origin to the centre of the dot Distance moved by the solvent from the origin to the solvent front See the image below for clarification of the equation. Tyrone John, Chartered Biologist 18

19 Chromatography was used to identify the intermediates in the Calvin Cycle. The experimental set up is shown below: Self-study exercises Instructions Go to and watch the video(s) and complete the following tasks. Completion date: 1. Make notes from the video(s) using the cornell grid. 2. Complete the following questions. Tyrone John, Chartered Biologist 19

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24 Practical No 2 Factors that affect the rate of photosynthesis. 1. Light Intensity There are several ways to measure the effect of light intensity of the rate of photosynthesis. One method is to use an indicator called hydrogen carbonate indicator (also called bicarbonate indicator). Below is an outline of the theory of this experiment: To measure how much photosynthesis is occurring we can use algae immobilised in alginate beads (these are called algal balls) and an indicator that will change colour based on the concentration of carbon dioxide. The indicator is called bicarbonate indicator. Bicarbonate indicator is very sensitive to changes in PH. At carbon dioxide concentrations of greater than 0.03% the indicator is yellow and carbon dioxide concentrations below 0.03% the indicator will turn purple. If the indicator is equilibrated with atmospheric carbon dioxide concentration (i.e. 0.03%) it will be orange/red in colour. See figure 1 below. Figure 1. Bicarbonate indicator colour changes due to PH. Tyrone John, Chartered Biologist 24

25 How to change the light intensity One way to do this is to alter the distance the algal balls and bicarbonate indicator are away from the light source. The closer to the light source the higher the light intensity and the further away from the light source the lower the light intensity. There is a rule, called the inverse square rule, that can be used to convert distance into relative light intensity. The rule is: Relative Light intensity = 1 D 2 This equation calculates the reciprocal of distance squared which equals relative light intensity. 1/D 2 produces numbers with many decimal places so an adjustment may be required to give a sensible number for analysis and plotting on a graph. For example, see table 1 below: Table 1. Conversion of relative light intensity to a more useable number by multiplying 1/D 2 by (10 4 ). In order to get more sensible numbers, I have multiplied the 1/D 2 value by (10 4 ). If you do this remember to state this on your graph and in your table that you have done this. It should be written like this: Relative light intensity 1/D 2 (x 10 4 ). Distance in cms 1/D 2 Multiply 1/D 2 by However, you could just write distance. Tyrone John, Chartered Biologist 25

26 Typical bicarbonate indicator colour change at normal atmospheric carbon dioxide concentrations, during no light and in bright light. The table below shows the colour change of bicarbonate indicator under different light intensities. Start point In the dark (covered with black sugar paper - paper removed for photograph) Near a lamp ph 8.4 (cherry red); 0.04% CO 2 in atmosphere ph 8.0 (yellow); more yellow because of increased CO 2 produced in respiration (creates carbonic acid). This CO 2 is not removed as photosynthesis does not proceed in the dark. ph 9.2 (purple); more purple because CO 2 is being removed from the indicator for use in photosynthesis. This reduces the amount of carbonic acid in the solution so it becomes more alkaline. Tyrone John, Chartered Biologist 26

27 Percentage transmission readings In this investigation you will use a colorimeter with a green filter. When the bicarbonate indicator is orange there will be a high percentage transmission of green light. As the bicarbonate indicator turns to purple the percentage transmission of green light will decrease. Typical apparatus for this experiment 1. 50cm 3 screw cap bottles. 2. A lamp. 3. A meter ruler. 4. A4/A3 boxes and possible black bin liners and clamp stands. 5. Algal balls. 6. Universal indicator solution. 7. Colorimeter. 8. Water bath. You will need to set up the apparatus similar to that shown below: Note how the tubes of offset from each other to allow each tube to receive light. The tubes will be covered with a box or black bin bag. Heat shield 150W halogen lamp metre-rule Tyrone John, Chartered Biologist 27

28 Extension The photosynthometer experiment A photosynthometer is shown below: With this apparatus you measure the distance moved by the air bubble over different light intensities. The oxygen released during photosynthesis will cause the bubble to move if this distance moved is measured over a given time then the rate of photosynthesis can be calculated by: Rate of photosynthesis = Distance moved by air bubble/mm time/s The volume of oxygen produce during photosynthesis can also be calculated by the equation: v = πd2 4 l Where: v = the volume of oxygen produced. d = to the diameter of the capillary tube. l = the length of the bubble of oxygen collected. Tyrone John, Chartered Biologist 28

29 Complete the following question: Tyrone John, Chartered Biologist 29

30 Tyrone John, Chartered Biologist 30

31 PUTTING IT ALL TOGETHER 1. Complete the crossword Tyrone John, Chartered Biologist 31

32 2. Put the following in the correct order using the answer grid on the next page. A. Energy is provided to the proton pumps that pump protons from the stroma into the thylakoid space. B. Protons diffuse out of the thylakoid space and into the stroma through the ATP synthetase. C. Light energy is absorbed by accessory pigments and is transferred to the chlorophyll a molecule in the reaction centre of both PS II and PS I. D. TP is also needed to regenerate RuBP via the production of Rup. E. RUBP is carboxylated to an unstable 6 carbon compound by the action of RUBISCO. F. GP is reduced to TP by NADPH 2. G. High energy electrons are caught by electron acceptors. H. The unstable six carbon compound breaks down to two molecules of GP. I. The electrons are ejected from the chlorophyll a molecule as high energy electrons. J. High energy electrons pass down the electron transport chain via a series of election carriers. K. Electrons lost from PSII are replaced by those created from the photolysis of water. L. ATP and NADPH 2 enter the Calvin cycle. M. 1 molecule of TP is used to produce other molecules outside of the Calvin cycle. N. The electrons in the chlorophyll a molecule are raised to a higher energy level. O. Rup is phosphorylated to RuBP. P. Electrons from PSI are used to produce ATP by cyclic photophosphorylation as well as to reduce NADP to NADPH 2. Q. A proton gradient is formed. R. Electrons enter PSI from PSII. S. This provides energy for the phosphorylation of ADP to ATP. T. ATP is also required for this step. Tyrone John, Chartered Biologist 32

33 Answer grid CORRECT ORDER LETTER Tyrone John, Chartered Biologist 33

34 3. Assertion & Reason In each of the following questions, a statement of assertion (A) is given and a corresponding statement of reason (R) is given just below it. Of the statements mark the correct answer as: (a) If both A and R are true and R is the correct explanation of A. (b) If both A and R are true but R is not the correct explanation of A. (c) If A is true but R is false. (d) If both A and R are false. Place your answer in the answer grid on the next page. 1. Assertion (A): High energy electrons are ejected from the reaction centre of both PSI and PSII. Reason (R): Light is absorbed by the photosystem. 2. Assertion (A): GP is reduced to TP. Reason (R): This reaction requires NADP. 3. Assertion (A): Oxygen is produced during non-cyclic photophosphorylation. Reason (R): Water undergoes photolysis. 4. Assertion (A): Plants have more than one type of light absorbing pigment. Reason (R): These pigments have different colours. 5. Assertion (A): Carbon dioxide is the major limiting factor for photosynthesis. Reason (R): Carbon dioxide is needed by the Calvin cycle. 6. Assertion (A): Blue light has lower energy than red light. Reason (R): Blue light has a lower frequency than red light. Tyrone John, Chartered Biologist 34

35 7. Assertion (A): Carbon dioxide can be fixed in the dark by previously illuminated leaves. Reason (R): The reactions do not require light and use the assimilatory power from the light reaction. 8. Assertion (A): Along with chlorophyll a, the carotenoids are called accessary pigments. Reason (R): They pass on the light energy absorbed by them to chlorophyll b. 9. Assertion (A): A solution of isolated chloroplasts illuminated with light of 700nm will show fluorescence. Reason (R): Elections from chlorophyll a are excited to a higher energy level. 10. Assertion (A): Isolated chloroplasts placed in a hypotonic solution and illuminated with light will not generate a proton gradient. Reason (R): The water potential of the solution is lower than the inside the chloroplast. Answer grid for Assertion and Reason Question Number Letter Tyrone John, Chartered Biologist 35

36 If you have given an answer of b for any of the above assertion and reason questions, write the correct explanation(s) below: Write at least one Assertion & Reason question of your own below: Tyrone John, Chartered Biologist 36

37 4. Multiple Choice Questions a) During fixation of one molecule of carbon dioxide the number of ATP and NADPH 2 required are. (a) 3 ATP and 2 NADPH 2 (b) 5 ATP and 2 NADPH 2 (c) 12 ATP and 12 NADPH 2 (d) 2 ATP and 3 NADPH 2 b) Protons produced by the photolysis of water accumulate within the. (a) (b) (c) (d) Thylakoid space. Stroma of the chloroplast. intermembrane space of the chloroplast. outside of the thylakoid space. c) Identify A, B, C and D in the diagram below. light B ADP +Pi ATP E C D A Tyrone John, Chartered Biologist 37

38 A B C D E (a) P700 H + acceptor e - acceptor P680 NADP (b) Photosystem e - acceptor Electron Photosystem NADPH 2 I transport chain II (c) Photosystem H + acceptor e - acceptor P700 NADPH 2 (d) II Photosystem II e - acceptor Electron transport chain d) Which of the following are mismatched. Photosystem I NADPH 2 (a) (b) (c) (d) Photosystem I - absorbs light of wavelength 700nm. Photosystem II gains electrons from the photolysis of water. Glycerate phosphate a three carbon molecule. Antennae complex contains hundreds of pigment molecules. e) Which graph shows the effect of temperature on the rate of photosynthesis. Tyrone John, Chartered Biologist 38

39 f) Which substance(s) is (are) used to make organic molecules during photosynthesis. I. Carbon dioxide II. ATP III. Oxygen IV. Water (a) (b) (c) (d) I only I and IV only I, II and IV only I, III and IV only g) What changes in carbon dioxide levels and temperature will most likely produce curve I instead of curve II. Carbon dioxide levels Temperature (a) Increase Decrease (b) Decrease Increase (c) Decrease decrease (d) Increase Increase Tyrone John, Chartered Biologist 39

40 h) The graph below shows the action spectrum of photosynthesis What are the labels for the y and x axes? y axis x axis (a) Light absorbed Wavelength of light (b) Wavelength of light Light intensity (c) Wavelength of light Rate of photosynthesis (d) Rate of photosynthesis Wavelength of light i) Which combination measures the rate of photosynthesis Direct measurement Indirect measurement (a) Oxygen production Biomass increase (b) Carbon dioxide uptake Biomass decrease (c) Oxygen uptake Biomass increase (d) Carbon dioxide production Biomass decrease Tyrone John, Chartered Biologist 40

41 j) What limiting factor of photosynthesis are represented by X and Y X Y (a) Carbon dioxide concentration Temperature (b) Temperature Carbon dioxide concentration (c) Light intensity Carbon dioxide concentration (d) Temperature Light intensity Write at least one multiple choice question of your own below: Tyrone John, Chartered Biologist 41

42 5. Short answer questions 1. Consider the image below and answer the questions that follow. (a) (i) Name the reactants A and X. A: X: (ii) Name products C and Y. C: Y: (iii) Name process B Tyrone John, Chartered Biologist 42

43 (iv) Name the intermediates D and E. D: E: (b) Name the structure L and describe how it is adapted to its function in photosynthesis. 2. Consider the diagram below and summarise the processes occurring at stages 1-8. Tyrone John, Chartered Biologist 43

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45 3. (a) Add the following labels and annotations to the diagram below: i. Stroma. ii. Granum. iii. Thylakoid membrane. iv. Thylakoid space. v. Outer membrane of the chloroplast. vi. Electron transport chain. vii. Splitting of water. viii. Synthesis of ATP and reduced NADP. ix. Calvin cycle. (b) How does the presence of organelles such as chloroplasts leads to a greater efficiency in biochemical pathways within cells? Tyrone John, Chartered Biologist 45

46 (c) Explain why light independent reactions is a better description of the Calvin cycle than the dark reactions. 4. Consider the diagram below and answer the questions that follow. Tyrone John, Chartered Biologist 46

47 (a) State the other name for GALP. (b) (c) (d) Alongside each of the compounds in the Calvin cycle draw the correct number of circles to represent the n umber of carbon atoms in the compound. Fill in the boxes below the Calvin cycle giving one example of a different type of organic molecule that the plant might synthesise from GALP. Summarise the processes occurring at each of the numbered stages in the diagram of the Calvin cycle. Tyrone John, Chartered Biologist 47

48 APPLICATION AND EXTENSION 1. Explain why the Calvin cycle is also known as the photosynthetic carbon reduction cycle (PCR). 2. Suggest advantages of the Calvin cycle being a cyclic series of reactions. 3. How many turns of the Calvin cycle are required to produce 1 triose phosphate molecule? Explain your answer. Tyrone John, Chartered Biologist 48

49 4. There are three known mechanisms by which carbon dioxide can be fixed into organic molecules. These mechanisms are called the C3, C4 and CAM pathways. State, with a reason, which pathway could be the Calvin cycle. 5. Read the information below and then answer the questions that follow. The light dependent reactions of photosynthesis require to different electron transport chains (ETC). one ETC transfers high energy electrons from photosystem II (PSII) to photosystem I (PSI), the other transfers high energy electrons from PSI to NADP. The transfer of electrons in both ETCs needs electron carriers which transfer electrons via oxidation and reduction of the electron carriers. Electron transfer between PSII and PSI requires three different electron carriers. These are, in order: i. Plastoquinone (PQ). This is a lipid soluble molecule. PQ becomes reduced by the aid of a protein, called D 1, when it becomes bound to PQ. ii. The cytochrome b 6 -f complex. This is a complex of proteins found within the thylakoid membrane. iii. Plastocyanin (PC). This is a small copper containing protein located within the thylakoid space. Electron transfer between PSI and NADP requires one electron carrier. This is called ferredoxin which contains iron and sulphur atoms and is located bound to the stroma side of PSI. Ferredoxin is a strong reducing agent and is capable of reducing NADP via an enzyme. The complete process of electron transfer from water to NADP by way of PSII and PSI is known as non-cyclic electron flow or the Z scheme. In an alternative Tyrone John, Chartered Biologist 49

50 process known as cyclic electron flow ferredoxin may recycle electrons back to PSI. Herbicides are chemicals that can kill plants. There are many different classes of herbicides and all of them have a specific modes of action. Some herbicides are inhibitors of photosynthesis others can inhibit the synthesis of carotenoids, while others can inhibit cellulose production or act as uncouples of oxidative phosphorylation. Inhibitors of photosynthesis can be sub classed into inhibitors of PSII or PSI. Examples of PSII inhibitors are: Diuron and Atrazine and examples of PSI inhibitors are: Diquat and Paraquat. The mode of action of some PSII inhibitors is to bind to the D 1 protein. The mode of action of some PSI inhibitors is to interact with ferredoxin and compete with NADP. (a) Examine the diagram on page 52 and answer the following questions. (i) State the names of the structures labelled A to J. A: B: C: D: E: F: G: H: Tyrone John, Chartered Biologist 50

51 I: J: (ii) Page 52 is labelled with the words TOP and BOTTOM. These words correspond to precise locations within the chloroplast. State what these locations are called: TOP: BOTTOM: (ii) Explain how the protons at point X are produced. (iii) Explain the likely function of the protons at Y. Tyrone John, Chartered Biologist 51

52 TOP Y 2H + G C C A 2e - B 2e - H J A 2H + 2e - 2e - F PSII Cytochrome b 6 -f Complex PSI D E 2H + X 2e - + 2H + = H 2 I Bottom Tyrone John, Chartered Biologist 52

53 (iv) Place the letter Z in the most likely location for protein D 1. Explain your answer. (b) The presence of weeds in crop fields can reduce the crop yield significantly. A farmer has expressed the problem of weeds on his farm as weeds start competing with the corn plant, it makes my skin crawl. Those weeds rob yield and nutrients, taking away from my bottom line. We want those weeds gone as soon as possible. A new corn herbicide has been developed to eradicate broadleaf weeds and grasses in corn fields. This new herbicide is called Acuron and has 4 different active ingredients, one being atrazine. The result of Acuron use is shown below. Tyrone John, Chartered Biologist 53

54 (i) What class of herbicide is atrazine? (ii) What type of electron flow does atrazine interrupt? (iii) What effect does atrazine have on the production of ATP and NADPH 2? Explain your answer. Tyrone John, Chartered Biologist 54

55 (iv) Explain how atrazine kills weeds. 6. Read the biological science review articles entitled RUBISCO the world s most important enzyme (answer questions a to e) and also read what is a limiting factor (answer questions f to g), in the photosynthesis reading material booklet, along with the information below and then answer the questions that follow. Photosynthesis evolved early in the earth s history. The rapidity of its emergence suggest it was no fluke. The timeline of photosynthesis on Earth is: 4.6 billion years ago The formation of the Earth. 3.4 billion years ago The first photosynthetic bacteria were formed. These bacteria absorbed near infrared rather than visible light and produced sulphur rather than oxygen billion years ago First rock evidence of atmospheric oxygen. Tyrone John, Chartered Biologist 55

56 2.7 billion years ago Appearance of cyanobacteria. These bacteria were the first oxygen producers. They absorb visible light using a mix of different pigments. 1.2 billion years ago The appearance of red and brown algae. These organisms have more complex cellular structures than bacteria do. Like cyanobacteria they contain a mix of different pigments billion years ago The appearance of green algae. Green algae do better than red and brown algae in the strong light of shallow water billion years ago The appearance of the first land plants. Mosses and liverworts descended from green algae and lacked vascular structures like stems and roots billion years ago The appearance of vascular plants. These plants are grasses, trees and cacti. They are able to grow tall to capture more light. (a) It is often said that RUBISCO is the most abundant enzyme in the world. This is due to the enormous number of plants on Earth that use RUBISCO. Do you agree with the latter statement? Explain your answer. (b) Under what atmospheric conditions is RUBISCO thought to have evolved? Tyrone John, Chartered Biologist 56

57 (c) To produce carbohydrates in photosynthesis, carbon dioxide must be reduced. The source, or donor, of this reducing power has changed/been added to over the course of Earth s history. (i) Name two different substances that can act as a source of reducing power for the reduction of carbon dioxide. (ii) Using your examples from ci, write simple equations to show how carbon dioxide is reduced and the products of this reduction. (iii) Between 2.9 and 2.4 billion years ago, scientists say that oxygenic photosynthesis arose. Suggest an explanation for the term oxygenic photosynthesis. (d) (i) RUBISCO can catalyse two different reactions in plant cells. Theses reactions are: carboxylation and oxygenation reactions. The reaction that occurs depends on the concentration of two gases. Write equations for carboxylation and oxygenation. Tyrone John, Chartered Biologist 57

58 (ii) Explain the problems that oxygenation reactions produce in the plant and how this problem is dealt with. (e) Explain the difference between aggregates and chaperones. (f) Do you agree with the statement as the enzyme loses its correct conformation, the active site is lost? Explain your answer. Tyrone John, Chartered Biologist 58

59 (g) An understanding of the limiting factors of photosynthesis are essential for the commercial growing of crops like tomatoes. This allows farmers to produce the ideal conditions that will maximise their crop yields. (i) State the law of rate limiting factors. (ii) State the factors that are most likely to limit the rate of photosynthesis. (iii) Explain how you would determine what factor is limiting the rate of photosynthesis. (iv) There is an economic rule called the law of diminishing returns. This law can be applied to biological situations like limiting factors of photosynthesis. (a) Suggest a definition for this law based on limiting factors. Tyrone John, Chartered Biologist 59

60 (b) Can the law of diminishing returns be applied to figure 4. If so, exactly where on the graph would this occur. Explain your answer. 7. An investigation was carried out into the effect of reducing the carbon dioxide available for photosynthesis. Cells of the unicellular alga were suspended in a solution containing 1% carbon dioxide. After 250 seconds, the carbon dioxide in the solution was reduced to 0.003%. The cells were illuminated with a bright light and some were removed at regular time intervals for 500 seconds. The concentrations of ribulose bisphosphate (RuBP) and Glycerate phosphate (GP) in the cells were measured. (i) Suggest two reasons why a suspension of cells of a unicellular alga, in solution, is more suitable for this investigation than using leaves. (ii) Suggest why it would be advisable to illuminate the cells at high light intensity during this investigation. Tyrone John, Chartered Biologist 60

61 (iii) The graph shows the results of the investigation. Describe and suggest an explanation for the changes in the concentrations of RuBP and GP shown in the graph. Tyrone John, Chartered Biologist 61

62 8. The Calvin cycle takes place in the stroma of the chloroplast. The flow chart below summarises the investigation that showed this. 1. Scientists produced a suspension of isolated chloroplasts. They added phosphate and NADP to this suspension. 2. They illuminated the suspension and bubbled air through it. The air contained no carbon dioxide. 3. The scientists then broke up the chloroplasts and centrifuged them. 4. They incubated the supernatant with radioactive carbon dioxide. 5. After a short time, the scientists found radioactive glycerate phosphate in the supernatant. Tyrone John, Chartered Biologist 62

63 (a) Phosphate and NADP were added to the chloroplast suspension (step 1). Name one other substance that must be added to ensure that the lightdependent reactions take place. (b) (i) Describe and explain what happened to the NADP that was added to the chloroplast suspension when it was illuminated (step 2). (iii) It was necessary to exclude carbon dioxide when the chloroplasts were illuminated (step 2). Explain why. (c) The results of this investigation show that the light independent reactions take place in the stroma of the chloroplast. Explain how. Tyrone John, Chartered Biologist 63

64 Concentration of radioactive substance 9. Algae are photosynthetic organisms. Scientists used algae to investigate the light-independent reaction, as outlined in the following pints: 1. They put some algae into a tank of water. They added carbon dioxide labelled with the radioactive isotope of carbon, 14 C, by bubbling it through the water in the tank. 2. They switched on a light and kept the algae illuminated for 12 hours. 3. After 12 hours, the scientists switched off the light. They kept the algae in the dark for a further 12 hours. 4. The scientists measured the concentration of radioactive GP, radioactive RuBP and radioactive glucose over the 24-hour period of the investigation. 5. The results of this investigation are shown in the graph below. Light Dark GP Glucose RuBP Time after radioactive carbon dioxide added / hours (a) Explain the change in the concentration of radioactive GP in the first 3 hours. Tyrone John, Chartered Biologist 64

65 (b) The concentration of radioactive GP stayed the same between 3 and 12 hours. Explain why. (c) Explain the changes that took place in the concentrations of radioactive GP and radioactive RuBP when the light was switched off. (d) What would you expect to happen to the concentration of radioactive glucose when the light was switched off? Explain your answer. Tyrone John, Chartered Biologist 65

66 10. Read the following information and answer the questions that follow. The effect of light intensity on the rate of photosynthesis can be determined by a number of experimental methods. One method uses a bicarbonate indicator to measure the concentration of carbon dioxide indirectly by a colour change, while other methods employ the direct volume measurement of carbon dioxide. Because plants, also, undertake respiration, its often common for rate of photosynthesis to be expressed as either net photosynthesis (NP) or gross photosynthesis (GP). GP and NP can be placed into an equation along with respiration (R) as shown below: GP = NP + R (eq 1) Plants, therefore, undertake respiration as well as photosynthesis. Respiration produces carbon dioxide and photosynthesis uses carbon dioxide. During conditions of light both respiration and photosynthesis occur, but in the absence of light only respiration occurs. The graph below shows the results of an experiment where two different species of plant, Oxalis acetosella (habitat forest floor) and Bellis perennis (habitat field), were subjected to increasing light intensities - measured in kiolux. The experiment was undertaken with ideal conditions to ensure maximum photosynthetic rate for each species of plant. Tyrone John, Chartered Biologist 66

67 A Rate of CO2 uptake/nmol cm -2 s -1 B Light Intensity/ Kilolux (a) Calculate the rate of carbon dioxide uptake between 20 and 35 lux for both line A and line B. Rate of carbon dioxide uptake for line A =. Rate of carbon dioxide uptake for line B =. Tyrone John, Chartered Biologist 67

68 (b) State two factors that would needed to have been controlled in this experiment. (c) Suggest, with an explanation, which lines show the results for Oxalis acetosella and Bellis perennis. (d) At which light intensity does GP = R for both line A and line B? Explain your answer. (e) State the name of the plant that has the lower rate of respiration and suggest how the plant could achieve these lower reparation rates. (f) For line B, suggest an explanation for why the rate of carbon dioxide uptake remains constant above 60 lux despite there no change in the rate of respiration? Tyrone John, Chartered Biologist 68