photosynthesis - exam 2023 with verified questions and answers

when plants are exposed to extreme high or cold temperatures for a continued period of time they are put under a lot of stress. this stress greatly impacts the rate of photosynthesis, in particular, the dight dependent reaction. explain why extreme cold leads to decrease in the LDR (2) there is less ATP and less NADP state where the light independent reaction takes place in photosynthetic plants (1) the stroma of the chloroplasts extreme cold can cause a decrease in rubisco activity.A decrease in the activity of the enzyme rubisco limits the rate of photosynthesis. Explain why (2) there will be less CO2 to react with RuBP meaning less GP is produced The photolysis of water is an important part of the process of photosynthesis. Describe what happens in the photolysis of water (2) water forms H+ and electrons. light excites electrons Describe the part played by chlorophyll in photosynthesis (3) chlorophyll absorbs light energy. raises energy levels of electrons and excites them. ATP is formed In photosynthesis, which chemicals are needed for the light-dependent reaction? (1) NADP, ADP, Pi and water describe what happens during photoionisation in the light dependent reaction (2) chlorophyll absorbs light energy, exciting the electrons and causing them to move out of the chlorophyll. once electrons are lost, chlorophyll becomes positively charged. give 2 products of the light dependent stage of photosynthesis (2) 1. ATP 2. NADPH describe the effect of light energy on the light dependent reaction of photosynthesis (2) excited electrons. releases electrons describe how NADP is reduced in the light-dependent reaction of photosynthesis (2) electrons released from photolysis in which part of a chloroplast do the light dependent reactions occur (1) thylakoids explain the role of chlorophyll in photolysis (3) absorbs light energy. becomes oxidised. accepts electrons from water explain how the energy of light is converted into chemical energy in the light-dependent reactions (3) electrons raised to a higher energy level. electron carriers are used for the production of ACT in the light-dependent reaction of photosynthesis, light energy generates ATP. describe how (5) light energy excites electrons in the chlorophyll. electrons pass down the electron transfer chain. electrons reduce carriers in a series of redox reactions. as electrons pass down the energy levels, energy is released. this energy is used to form ATP from ADP and Pi crops use light energy to produce photosynthetic products. describe how crop plants use light energy during the light-dependent reaction (5) light energy excited electrons in the chlorophyll so they are removed. electrons move along the electron transport chain releasing energy as they go down each energy level. this energy is used to join ADP and Pi to make ATP. photolysis of water produces protons, electrons and oxygen. NADP is reduced by electrons describe the role of electron transport chains in the light dependent reactions of photosynthesis (6) electron transport chain accepts excited electrons from chlorophyll. electrons lose energy along the electron transport chain. ATP produced from ADP and Pi. reduced NADP formed when electrons from transport chain and H+ combine with NADP. H+ comes from photolysis In which part of a chloroplast does the light-independent reaction occur? (1) stroma Which process is the source of the ATP used in the conversion of glycerate 3-phosphate (GP) to triose phosphate? (1) light-dependent reaction What proportion of triose phosphate molecules is converted to ribulose bisphosphate (RuBP)? (1) 5/6 Lowering the temperature has very little effect on the light-dependent reaction, but it slows down the light-independent reaction. Explain why the light-independent reaction slows down at low temperatures. (2) enzymes involved. slow rate of enzyme reaction at low tempuratures. less kinetic energy so fewer collisions ATP and reduced NADP are two products of the light-dependent reactions. Describe one function of each of these substances in the light-independent reactions. (2) ATP - provides energy to convert GP into TP NADP - provides electrons to reduce GP to TP During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how. (5) carbon dioxide combines with ribulose bisphosphate this produces 2 glycerate phosphate (GP). BP is then reduced to triose phosphate (TP) using reduced NADP and energy from ATP. TP is converted to glucose. give one dependent variable you could measure in order to determine the rate of photosynthesis in an aquatic plant (1) measure the volume of gas a suspension of chloroplasts was isolated from an aquatic plant and a reagent was added. the reagent is blue when oxidised and is colourless when reduced. the suspension of chloroplasts in blue reagent was exposed to sunlight. the blue colour disappeared. use your knowledge of the light-dependent reactions of photosynthesis to explain why (2) chlorophyll excited electrons from chlorophyl changes the dye colour describe the role of electrons in the production of ATP in the light-dependent reaction, after photoionisation has taken place (5) the electrons pass down the electron transport chain releasing energy energy is used to generate a proton gradient across the thylakoid membrane protons move down concentration gradient into storm via ATP synthase releasing energy allowing ADP and Pi to make ATP suggest why cells might be supplies with radioactively labelled 14CO2 in an experiment (1) used in photosynthesis to allow the detection of products explain how a lack of light would cause the amount of radioactively labelled GP in an experiment to rise (2) ATP and reduced NADP not formed GP is not being used to form RuBP explain what would cause the amount of radioactively labelled glucose to decrease when the light was switched off in an experiment (1) used in respiration some bacteria use hydrogen sulphide to produce organic compounds. the hydrogen sulphide has a similar role to that of water in photosynthesis. a simple equation for this process in bacteria is shown below: hydrogen sulphide + carbon dioxide - glucose + sulphur + water suggest what the hydrogen sulphide is used for in these bacteria provides hydrogen and electrons for reduction source of electrons for chlorophyll heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. heat stress is a major factor in limiting the rate of photosynthesis. heat stress decreases the light dependent reactions of photosynthesis. explain why this leads to a decrease in the light independent reaction less ATP less reduced NADP heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. heat stress is a major factor in limiting the rate of photosynthesis. another effect of heat stress is a decrease in the activity of the enzyme rubisco. a decrease in the activity of an enzyme means that the rate of the reaction it catalyses becomes slower A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis. explain why (2) less CO2 reacts with RuBP less GP the concentration of carbon dioxide in the air at different heights above ground in a forest changes over a period of 24 hours. use your knowledge of photosynthesis to describe these changes and explain why they occur (5) high conc of co2 linked with night no photosynthesis in the dark in dark places plants respire in light, the net uptake of co2 by plants is more co2 than they produce. rate of photosynthesis is greater than the rate of respiration decrease in co2 conc with height at ground level there are fewer leaves in the light independent reaction of photosynthesis, the carbon in carbon dioxide becomes carbon in triose phosphate. describe how (5) co2 combines with RuBP to produce 2 mol of GP reduced to triose phosphate TP requires reduced NADP energy from ATP