PPQ Practising Specific Skills

Transcription

1 PPQ Practising Specific Skills 5. Short Answers Skills Name: Class: Date: Time: 9 minutes Marks: 50 marks Comments: Page of 85

2 During respiration where, exactly, in a cell does each of the following occur? (i) Glycolysis () Electron transfer chain () Without oxygen, less ATP is produced by respiration. Explain why. (Total 4 marks) The diagram represents two of the stages of aerobic respiration that take place in a mitochondrion. Name substance X. () Which stage of aerobic respiration takes place inside a mitochondrion and is not represented on the diagram? () Page of 85

3 (c) Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion. (3) (Total 5 marks) 3 Some plant seeds can respire aerobically and anaerobically. A summary of the process of anaerobic respiration is shown below. (i) Where in a cell does stage occur?... () Explain how stage enables stage to continue Page 3 of 85

4 The Respiratory Quotient (RQ) can provide information on the type of respiration taking place in an organism. The following equation is used to calculate the RQ. (i) What would be the RQ for aerobic respiration of glucose? () A student calculated that the RQ of germinating seeds was.8. Use the information provided to explain this result (c) Aerobic respiration produces more ATP per molecule of glucose than anaerobic respiration. Explain why (Total 8 marks) 4 Describe how acetylcoenzyme A is formed in the link reaction Page 4 of 85

5 In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form six-carbon citrate. This reaction is catalysed by the enzyme citrate synthase. (i) Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. This induces a change in the enzyme, which enables the acetylcoenzyme A to bind. Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the enzyme Another substance in the Krebs cycle is called succinyl coenzyme A. This substance has a very similar shape to acetylcoenzyme A. Suggest how production of succinyl coenzyme A could control the rate of the reaction catalysed by citrate synthase (c) In muscles, pyruvate is converted to lactate during anaerobic respiration. (i) Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration Page 5 of 85

6 In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this () (Total 9 marks) 5 The table contains statements about three stages of respiration. Complete the table with a tick if the statement in the first column is true for each stage of respiration in an animal. Occurs in mitochondria Carbon dioxide produced Glycolysis Link reaction Krebs cycle NAD is reduced (3) The following reaction occurs in the Krebs cycle. A scientist investigated the effect of the enzyme inhibitor malonate on this reaction. The structure of malonate is very similar to the structure of succinate. The scientist added malonate and the respiratory substrate, pyruvate, to a suspension of isolated mitochondria. She also bubbled oxygen through the suspension. (i) Explain why the scientist did not use glucose as the respiratory substrate for these isolated mitochondria Page 6 of 85

7 Explain how malonate inhibits the formation of fumarate from succinate (iii) The scientist measured the uptake of oxygen by the mitochondria during the investigation. The uptake of oxygen decreased when malonate was added. Explain why (Total 9 marks) 6 The table contains statements about three biological processes. Complete the table with a tick if the statement in the first column is true, for each process. Photosynthesis Anaerobic respiration Aerobic respiration ATP produced Occurs in organelles Electron transport chain involved (3) Write a simple equation to show how ATP is synthesised from ADP. () Page 7 of 85

8 (c) Give two ways in which the properties of ATP make it a suitable source of energy in biological processes (d) Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. 7 Where precisely in a cell does the Calvin cycle take place?... (Total 8 marks) () Page 8 of 85

9 A scientist investigated the effect of changing the carbon dioxide concentration on the amounts of glycerate-3-phosphate (GP) and ribulose bisphosphate (RuBP) in photosynthesising cells. The graph shows the results obtained when the carbon dioxide concentration was reduced. (i) Explain the decrease in the amount of GP after the carbon dioxide concentration was reduced () The scientist carried out a similar experiment but increased the carbon dioxide concentration from % to %. The relative amounts of GP and RuBP remained the same. Suggest two reasons why Page 9 of 85

10 (c) Some bacteria use hydrogen sulfide, H S, to produce organic compounds. The hydrogen sulfide has a similar role to that of water in photosynthesis. A simple equation for this process in bacteria is shown below: hydrogen sulfide + carbon dioxide glucose + sulfur + water Suggest what the hydrogen sulfide is used for in these bacteria (Total 6 marks) 8 The diagram shows part of the nitrogen cycle. Which one of the processes P, Q or R involves nitrification? () Page 0 of 85

11 The diagram above includes one process in which microorganisms add ammonium ions to soil. Describe another process carried out by microorganisms which adds ammonium ions to soil (c) Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil (d) One farming practice used to maintain high crop yields is crop rotation. This involves growing a different crop each year in the same field. Suggest two ways in which crop rotation may lead to high crop yields (Total 7 marks) Page of 85

12 9 The graph shows how gross productivity and biomass in an area changed with time in the succession from bare soil to mature woodland. (i) Suggest appropriate units for gross productivity... () Explain the decrease in gross productivity as the woodland matures Use your knowledge of succession to explain the increase in biomass during the first 0 years [Extra space] (3) Page of 85

13 (c) Use the information in the graph and your knowledge of net productivity to explain why biomass shows little increase after 00 years (d) Suggest one reason for conserving woodlands () (Total 9 marks) 0 Upwelling is a process where water moves from deeper parts of the sea to the surface. This water contains a lot of nutrients from the remains of dead organisms. (i) Nitrates and phosphates are two of these nutrients. They provide a source of nitrogen and phosphorus for cells. Give a biological molecule that contains:. nitrogen.... phosphorus... Page 3 of 85

14 Describe the role of microorganisms in producing nitrates from the remains of dead organisms (Extra space) (3) Upwelling often results in high primary productivity in coastal waters. Explain why some of the most productive fishing areas are found in coastal waters (Total 7 marks) Farmland previously used for growing crops was left for 30 years and developed into woodland. During this period, ecologists recorded an increase in the diversity of birds in the area. Name the process that resulted in the development of woodland from farmland... () Page 4 of 85

15 Explain the increase in the diversity of birds as the woodland developed (Extra space) (3) (c) The ecologists also investigated photosynthesis in two species of plant found in the woodland. One of the species was adapted to growing in bright sunlight (sun plant) and the other was adapted to growing in the shade (shade plant). The ecologists results are shown in the figure below. (i) Give two factors which could be limiting the rate of photosynthesis in the sun plant between points A and B on the figure.. () Page 5 of 85

16 Explain why CO uptake is a measure of net productivity..... (Extra space)..... () (iii) Use the information in the figure to explain how the shade plant is better adapted than the sun plant to growing at low light intensities (Extra space)..... (Total 8 marks) The diagram shows the nitrogen cycle. (i) Name process P... () Page 6 of 85

17 Name process Q... () Leguminous crop plants have nitrogen-fixing bacteria in nodules on their roots. On soils with a low concentration of nitrate ions, leguminous crops often grow better than other types of crop. Explain why (c) Applying very high concentrations of fertiliser to the soil can reduce plant growth. Use your knowledge of water potential to explain why (Total 6 marks) Page 7 of 85

18 3 Intensive rearing of livestock produces large quantities of waste. Some farmers use an anaerobic digester to get rid of the waste. In an anaerobic digester, microorganisms break down the large, organic molecules in the waste. This produces methane, which is a useful fuel. It also produces organic substances that can be used as a natural fertiliser. The diagram shows an anaerobic digester. (i) Suggest two advantages of processing waste in anaerobic digesters rather than in open ponds The anaerobic digester has a cooling system, which is not shown in the diagram. Without this cooling system the digester would soon stop working. Explain why. Page 8 of 85

19 (i) The over-application of fertiliser increases the rate of leaching. Explain the consequences of leaching of fertiliser into ponds and lakes. (Extra Space)... (3) Give one advantage of using natural fertiliser produced in the digester rather than an artificial fertiliser. () (Total 8 marks) 4 Urea from animal waste can be used as a fertiliser. Some bacteria in the soil secrete the enzyme urease which hydrolyses urea into ammonia. Some of this ammonia is released into the atmosphere. NBPT is an inhibitor of urease and can be added to urea fertiliser to reduce the loss of ammonia to the atmosphere. A molecule of NBPT has a similar structure to a molecule of urea. Use this information to suggest how NBPT inhibits the enzyme urease. Page 9 of 85

20 Scientists investigated the effect of NBPT on the release of ammonia from urea fertiliser added to the soil. A control experiment was carried out. This involved adding urea fertiliser only. The graph shows their results. (i) Describe how NBPT affected the loss of ammonia from urea fertiliser. () Page 0 of 85

21 Suggest an explanation for the increase in mass of ammonia released over the first four days in the control experiment. (c) Suggest how the addition of NBPT to urea fertiliser could result in increased growth of crop plants. (3) (Total 8 marks) 5 Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 6 molecules of ATP for each molecule of nitrogen that is reduced. Nitrogen gas is the usual substrate for this enzyme. Name the product. () Nitrogenase also catalyses reactions involving other substances. Explain what this suggests about the shapes of the molecules of these other substances. Page of 85

22 (c) (i) Azotobacter is a nitrogen-fixing bacterium. It produces the enzyme nitrogenase. The enzyme only works in the absence of oxygen. Azotobacter has a very high rate of aerobic respiration compared with bacteria that do not fix nitrogen. Suggest two advantages of the very high rate of aerobic respiration. If scientists could transfer the gene that codes for nitrogenase to cereal plants, these cereal plants would be able to fix nitrogen. However, the scientists would expect these genetically engineered cereal plants to grow more slowly than cereal plants that get their nitrogen from fertiliser. Explain why they would grow more slowly. (Total 7 marks) 6 When fertilisers are applied to fields next to a lake, nitrogen-containing substances from the fertilisers get into the lake. (i) Describe how the nitrogen-containing substances get into the lake. () Page of 85

23 It takes longer for the nitrogen-containing substances to get into the lake when an organic fertiliser is used than when an inorganic fertiliser is used. Explain why it takes longer when an organic fertiliser is used. Describe how the presence of nitrates in a lake may eventually lead to the death of fish. (4) (Total 7 marks) 7 In the activated sludge method of sewage treatment, organic matter in untreated sewage supplies nutrients to bacteria in the treatment tank. These bacteria include decomposers and nitrifying bacteria. The bacteria are eaten by ciliated protoctistans, which are, in turn, eaten by carnivorous protoctistans. (i) Explain the roles of the decomposers and the nitrifying bacteria in converting nitrogen in organic compounds in the sewage into a soluble, inorganic form. (3) Page 3 of 85

24 Nitrifying bacteria are one kind of bacteria that are important in the nitrogen cycle; nitrogen-fixing bacteria are another kind. Describe the part played by nitrogen-fixing bacteria in the nitrogen cycle. Page 4 of 85

25 The organic matter in untreated sewage consists of small particles, which are suspended in water. Activated sludge consists of solid lumps (flocs) of organic matter and bacteria. When the two are mixed in the treatment tank, bacteria from the flocs become dispersed in the water and feed on the suspended organic matter, converting it to flocs. Different types of ciliated protoctistans feed on the bacteria. Free-swimming protoctistans are able to move throughout the tank. Crawling protoctistans can only move over the surface of the flocs. The diagram shows the change in the nature of the organic matter in the treatment tank and the changes in the numbers of the different types of organisms present. Page 5 of 85

26 (i) Explain the changes in the numbers of dispersed bacteria and the numbers of free-swimming protoctistans. (3) Explain how the changes that occur in the treatment tank illustrate the process of succession. (4) (Total marks) Page 6 of 85

27 8 The diagram summarises the process of anaerobic respiration in yeast cells. (i) In anaerobic respiration, what is the net yield of ATP molecules per molecule of glucose? () Give two advantages of ATP as an energy-storage molecule within a cell Describe how NAD is regenerated in anaerobic respiration in yeast cells. () (Total 4 marks) Page 7 of 85

28 9 The diagram shows part of the nitrogen cycle. Name processes P and Q. P... Q... It is estimated that, each year, a total of tonnes of ammonia are converted to nitrate. Only 0 8 tonnes of ammonia are produced from nitrogen gas. Explain the difference in these figures. (c) The conversion of ammonia to nitrate involves oxidation. What evidence in the diagram supports this? () (Total 5 marks) Page 8 of 85

29 0 The diagram shows the structure of a chloroplast. (c) Label the diagram with an X to show where the light-dependent reactions take place and with a Y to show where the light-independent reactions take place. The photolysis of water is an important part of the process of photosynthesis. Describe what happens in the photolysis of water. 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. ATP. Reduced NADP... () (Total 5 marks) Page 9 of 85

30 The diagram gives an outline of the process of aerobic respiration. Page 30 of 85

31 Name substances X, Y and Z. X... Y... Z... (3) Give the location of each of the following in a liver cell. (i) Glycolysis... The Krebs cycle... (c) (i) Write the letter A on the diagram to show one step where ATP is used. Write the letter B on the diagram at two steps where ATP is produced. (3) (d) Apart from respiration, give three uses of ATP in a liver cell (3) (e) Human skeletal muscle can respire both aerobically and anaerobically. Describe what happens to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to human skeletal muscle. (4) (Total 5 marks) Page 3 of 85

32 Pyruvate is formed in the breakdown of glucose during respiration. When there is sufficient oxygen, this pyruvate is fully broken down. Name two substances formed from the pyruvate () (i) If there is a shortage of oxygen in muscle cells during exercise, some pyruvate is converted into lactate. Explain why muscles become fatigued when insufficient oxygen is available. Some of the lactate is oxidised to pyruvate by muscles when they are well-supplied with oxygen. Suggest an advantage of the lactate being oxidised in the muscles. (Total 5 marks) 3 Name the type of bacteria which convert (i) nitrogen in the air into ammonium compounds; nitrites into nitrates. Page 3 of 85

33 (i) Other than spreading fertilisers, describe and explain how one farming practice results in addition of nitrogen-containing compounds to a field. Describe and explain how one farming practice results in the removal of nitrogencontaining compounds from a field. (Total 6 marks) 4 Name the two substances produced by anaerobic respiration in humans When an athlete runs in a 00 metre race, 90% of the energy needed is provided by anaerobic respiration. (i) Explain why most of the energy is provided by anaerobic respiration rather than aerobic respiration. Page 33 of 85

34 The athlete continues to breathe deeply for several minutes after the race ends. Explain why this is necessary. (Total 6 marks) 5 The diagram shows the structure of a mitochondrion. In which part of the mitochondrion does the Krebs cycle take place? () Name two substances for which there would be net movement into the mitochondrion Page 34 of 85

35 (c) The mitochondria in muscles contain many cristae. Explain the advantage of this. (Total 5 marks) 6 The diagram shows the flow of energy through a marine ecosystem. Give one reason why not all the light energy falling on the producers is used in photosynthesis. () Page 35 of 85

36 The producers in this ecosystem are seaweeds, which have a large surface area to volume ratio. Give two advantages to seaweeds of having a large surface area to volume ratio S (c) Some species of seaweed are submerged in water for most of the time. Explain how being under water might affect the rate of photosynthesis. (3) (Total 6 marks) Page 36 of 85

37 7 Pea plants are leguminous and have nodules on their roots which contain bacteria that are able to fix nitrogen. The diagram shows some of the processes involved in nitrogen fixation by these bacteria. Name (i) substance X; () substance Y. () S Pea plants respire aerobically, producing ATP which can be used for amino acid synthesis. Describe the role of oxygen in aerobic respiration. Page 37 of 85

38 S (c) The bacteria respire anaerobically. This produces hydrogen and ATP used in nitrogen fixation. The hydrogen comes from reduced NAD. Explain how the regeneration of NAD in this way allows ATP production to continue. S (d) The enzyme nitrogenase is specific to the reaction shown. Explain how one feature of the enzyme would contribute to this specificity. Feature Explanation S (e) Sodium ions act as a non-competitive inhibitor of the enzyme nitrogenase. Explain how the presence of a non-competitive inhibitor can alter the rate of the reaction catalysed by nitrogenase. (3) (Total marks) Page 38 of 85

39 8 A hedgerow is a line of shrubs and trees bordering a field, together with the herbaceous plants at their base. In the last 50 years farmers have removed many hedgerows. Explain two advantages for a farmer of removing hedgerows In recent years some hedgerows have been replanted. Ground beetles, which are unable to fly, are predators of crop pests. The beetles overwinter in the shelter of grasses at the base of the hedgerow. In some large fields, a permanent strip of grass is left as shown in the diagram. Suggest and explain the advantage of leaving the strip of grass in the middle of the field. Page 39 of 85

40 (c) Apart from providing a habitat for predators of crop pests, give two biological benefits of replanting hedgerows (Total 6 marks) 9 The boxes in the diagram represent substances in glycolysis, the link reaction and the Krebs cycle. Complete the diagram to show the number of carbon atoms present in one molecule of each compound. Page 40 of 85

41 Other substances are produced in the Krebs cycle in addition to the carbon compounds shown in the diagram. Name three of these other products (3) (Total 5 marks) 30 The diagram shows a summary of the light-independent reaction of photosynthesis. (i) Complete the boxes to show the number of carbon atoms in the molecules. In which part of a chloroplast does the light-independent reaction occur? () (iii) Which process is the source of the ATP used in the conversion of glycerate 3-phosphate (GP) to triose phosphate? () (iv) What proportion of triose phosphate molecules is converted to ribulose bisphosphate (RuBP)? () Page 4 of 85

42 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. (Total 7 marks) 3 Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the advantage of mitochondria in muscle cells having more cristae. Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X has three carbon atoms. (i) Name substance X. () In the link reaction substance X is converted to a substance with molecules effectively containing only two carbon atoms. Describe what happens in this process. Page 4 of 85

43 (c) The Krebs cycle, which takes place in the matrix, releases hydrogen ions. These hydrogen ions provide a source of energy for the synthesis of ATP, using coenzymes and carrier proteins in the inner membrane of the mitochondrion. Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP. (3) (Total 8 marks) 3 In autumn when there is no crop, farm land may be used to grow mustard. The mustard absorbs nitrates which otherwise can leach out of the soil at this time of the year. The mustard is ploughed back into the soil just before sowing of the main crop in the spring. Nitrogen compounds in the mustard plants are made available for the main crop after ploughing in spring. Describe the role of microorganisms in this process. (5) Page 43 of 85

44 Explain why it is important for the farmer to reduce the leaching of nitrates. S (c) Plants absorb a number of other nutrients from the soil including phosphates. Describe why phosphates are needed by a growing plant. (4) (Total marks) 33 When one mole of glucose is burned, 800 kj of energy are released. However, when one mole of glucose is respired aerobically, only 40% of the energy released is incorporated into ATP. Each mole of glucose respired aerobically produces 38 moles of ATP. (i) Calculate how much energy is incorporated into each mole of ATP. Show your working. Answer... kj Page 44 of 85

45 When glucose is respired what happens to the energy which is not incorporated into ATP? () (i) When one mole of glucose is respired anaerobically, only moles of ATP are produced. Explain why less energy is released in anaerobic respiration. () At the end of a sprint race, a runner continues to breathe rapidly for some time. Explain the advantage of this. (Total 6 marks) Page 45 of 85

46 34 Tomato growers have increased the yield of fruit from 00 to 400 tonnes per hectare by growing the tomato plants in automatically heated glasshouses and enhancing the carbon dioxide concentration. To control the nutrient supply to the roots, the plants are grown without soil in plastic troughs, as shown in the diagram. Explain how enhancing the carbon dioxide concentration helps to increase the yield. Maintaining a high temperature in a glasshouse in winter, when the light intensity is low, may reduce the yield. Explain how. Page 46 of 85

47 S (c) Tomato fruits have a high percentage of water. When making tomato ketchup, it is more economical to use fruits which have a low percentage of water. Growers can reduce the water content of the fruit by adding sodium chloride to the nutrient solution in the plastic trough. Explain how adding sodium chloride can reduce the water content of the fruit. (Total 6 marks) 35 (i) Give two products of the light-dependent stage of photosynthesis The products of the light-dependent stage are used in the light-independent stage of photosynthesis. What are these products used for? () Page 47 of 85

48 The graph shows the rate of uptake or release of carbon dioxide by a plant at different light intensities. Explain the rate of carbon dioxide exchange at point X. (Total 5 marks) Page 48 of 85

49 Mark schemes (i) Cytoplasm; Accept - cytosol Inner membrane of mitochondrion Icristae; Reject crista/ particle Oxygen is the termina/ acceptor; (No) electron transfer chain / proton transfer / no oxidative phosphorylation; Accept ETC abbreviation Which produces most of the ATP (in aerobic respiration); Only glycolysis takes place; Pyruvate used to make lactate; Accept lactic acid Only produces (net) ATP (per molecule of glucose); Accept only 4 ATP are made max [4] pyruvate; Krebs cycle; (c) ATP formed as electrons pass along transport chain; oxygen is terminal electron acceptor / accepts electrons from electron transport chain / electrons cannot be passed along electron transport chain if no O to accept them; forms H O / accepts H + from reduced NAD / FAD / oxidises reduced NAD / FAD; 3 [5] Page 49 of 85

50 3 (i) Cytoplasm/cytosol;. Regenerates/produces NAD / oxidises reduced NAD;. NAD reduced in stage /glycolysis / NAD accepts hydrogen in stage /glycolysis; (i) /one/.0; Note: penalise use of NADP for first marking point obtained. Do not accept NAD accepts only protons but allow accepts protons and electrons.. Aerobic and anaerobic respiration occurring; Accept: some/mainly anaerobic respiration occurring.. More carbon dioxide produced than oxygen uptake; (c). Oxygen is final/terminal (electron) acceptor / oxygen combines with electrons and protons;. (Aerobic respiration) oxidative phosphorylation / electron transfer chain; 3. Anaerobic (respiration) only glycolysis occurs / no Krebs / no link reaction; Ignore: number of ATP produced. 3. Accept: without oxygen. 3. Ignore: converse. max [8] 4. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released;. Addition of coenzyme A. Accept: NAD reduced for oxidation (i). Change (in shape) of active site / active site moulds around the substrate; Reject: reference to inhibitor Accept: change in tertiary structure affecting active site. (Substrate / active site) now complementary. Neutral: references to two active sites. Is a competitive inhibitor / attaches to active site; Neutral: reference to inhibitor forming an enzyme-substrate complex. Reduces / prevents enzyme-substrate / E-S complex forming. Accept: Reduces / prevents acetylcoenzyme A binding to enzyme / citrate synthase Page 50 of 85

51 (c) (i). Regenerates / produces NAD / oxidises reduced NAD;. (NAD used) in glycolysis. Accept: description of glycolysis Accept: glycolysis can continue / begin (Pyruvate used) in aerobic respiration / (lactate / lactic acid) is toxic / harmful / causes cramp / (muscle) fatigue. Accept: (pyruvate) can enter link reaction Accept: reduces cramp / (muscle) fatigue Neutral: reduces muscle aches [9] 5 Glycolysis Link reaction Krebs cycle Occurs in mitochondria Carbon dioxide produced NAD is reduced Mark horizontally 3 (i). Glucose is used / broken down during glycolysis / in cytoplasm;. Accept: glucose to pyruvate or glucose not converted to pyruvate for one mark. Glucose cannot cross mitochondrial membrane(s) / pyruvate can cross mitochondrial membrane(s);. Is a competitive inhibitor / attaches to active site; Accept: inhibitor / malonate attaches to active site to form an enzyme-substrate complex. Reduces / prevents enzyme-substrate / E-S complex forming; Accept: substrate / succinate cannot bind to enzyme Accept mark point, but not mp in context of non-competitive inhibition Page 5 of 85

52 (iii). Krebs cycle inhibited as NAD / Coenzyme / FAD not / less reduced;. Hydrogens not passed to ETC therefore oxygen not used as (much as a) final / terminal (electron) acceptor; [9] 6 Photosynthesis Anaerobic respiration Aerobic respiration ATP produced Occurs in organelles Electron transport chain involved mark per column Mark ticks only. Ignore anything else if different symbols such as crosses are used as well. If crosses are used instead of ticks allow cross as equivalent to a tick. Reject tick with a line through 3 ADP + P i ATP; Both sides correct, but allow other recognised symbols or words for phosphate ion. Reject P unless in a circle. Accept = as equivalent to arrow Accept reversible arrow Ignore any reference to kj / water (c). Energy released in small / suitable amounts;. Soluble; 3. Involves a single / simple reaction;. In context of release, not storage. Ignore producing energy / manageable amounts.. Reject "broken down easily / readily". Reject "quickly / easily resynthesised". max Page 5 of 85

53 (d). ATP cannot be stored / is an immediate source of energy;. ATP only releases a small amount of energy at a time; [8] 7 Stroma (of chloroplasts); Reject: stoma. Reject: stroma of chlorophyll or any reference to chlorophyll. Accept: stroma of chloroplasts. (i) (Less) RuBP combines with carbon dioxide; Accept: binds/joins.. Temperature is a limiting factor/below optimum;. Light is a limiting factor/below optimum; Accept: limited by reduced NADP or ATP. 3. Limited by RuBP (available/produced); Accept: RuBP will always give GP (at high CO ). 4. Limited by enzyme; Accept: limited by Rubisco. (c). (Provides) hydrogen / protons/h + and electrons/e - ; Ignore: if water is used as source of hydrogen.. For reduction; Reject: reduction of NAD. Reject: reduction by H + or protons on their own. 3. Source of electrons for chlorophyll/electron transfer chain; Accept: electrons for photophosphorylation. Ignore: photosystems., and 3. Reject: reference to respiration/mitochondria. max max [6] 8 R.. Protein / amino acids broken down (to ammonium ions / ammonia); Accept: nucleic acids / RNA / DNA / urea / any named nitrogen containing compound as an alternative to protein / amino acids Accept: saprophytes / saprotrophs. By saprobionts / saprobiotic (microorganisms). Neutral: decomposers Reject: answers where incorrect type of bacteria given as saprobionts e.g. Nitrogen fixing bacteria Page 53 of 85

54 (c). (Fertility increased as) more nitrate formed / less nitrate removed / broken down; Accept: Nitrate remains. Less / no denitrification / process P is decreased / fewer denitrifying bacteria. Accept: more nitrification / more nitrifying bacteria / process R is increased (d). Grow crops / plants with nitrogen-fixing (bacteria); Accept: grow legumes / named example e.g. peas, beans, clover Accept: fallow year Accept: use different amounts of ions / nutrients. (Different crops use) different minerals / salts / nutrients / ions (from the soil); 3. (Different crops have) different pests / pathogens / diseases. max [7] 9 (i) Unit of energy / mass, per area, per year.. Less light / more shading / more competition for light; Neutral: references to animals. Reduced photosynthesis. Accept: no photosynthesis. Pioneer species;. Change in abiotic conditions / less hostile / more habitats / niches; Accept: named abiotic change or example of change e.g. formation of soil / humus / organic matter / increase in nutrients Neutral: reference to change in environment unqualified Neutral: more hospitable / habitable / homes / shelters 3. Increase in number / amount / diversity of species / plants / animals. Accept: other / new species (colonise) (c). Net productivity = gross productivity minus respiratory loss;. Decrease in gross productivity / photosynthesis / increase in respiration. 3 Page 54 of 85

55 (d). Conserving / protecting habitats / niches;. Conserving / protecting (endangered) species / maintains / increases (bio) diversity; 3. Reduces global warming / greenhouse effect / climate change / remove / take up carbon dioxide; 4. Source of medicines / chemicals / wood; 5. Reduces erosion / eutrophication. Accept: tourism / aesthetics / named recreational activity max [9] 0 (i). Amino acid / protein / enzyme / urea / nucleic acid / chlorophyll / DNA / RNA / / ATP / ADP / AMP / NAD / NADP;. DNA / RNA / nucleic acid / ATP / ADP / AMP / NADP / TP / GP / RuBP / phospholipids;. and. Accept any named equivalent examples e.g. nucleotides. Neutral: ammonia / nitrite / nitrate / phosphate.. Saprobiotic (microorganisms / bacteria) break down remains / dead material / protein / DNA into ammonia / ammonium; Accept: saprobionts / saprophytes / saprotrophs Neutral: decomposer. Ammonia / ammonium ions into nitrite and then into nitrate; Allow correct chemical symbols. Accept: correct answers which use incorrect bacteria e.g. nitrogenfixing but then reject m.p (By) Nitrifying bacteria / nitrification; 3. Nitrate / phosphate / named ion / nutrients for growth of / absorbed / used by plants / algae / producers;. More producers / consumers / food so more fish / fish reproduce more / fish grow more / fish move to area; Must have idea of more plants related to some increase in fish. [7] Succession; Ignore any word in front of succession e.g. secondary / ecological succession. Neutral forestation. Page 55 of 85

56 . Greater variety / diversity of plants / insects / more plant / insect species; Neutral: more plants.. More food sources / more varieties of food; Neutral: more food / more / greater food source (singular). 3. Greater variety / more habitats / niches; Accept: more nesting sites. Q Neutral: more homes / shelters. (c) (i) Temperature and carbon dioxide; Neutral: water, chlorophyll. 3 Shows (gross) photosynthesis / productivity minus respiration / more carbon dioxide used in photosynthesis than produced in respiration; Correct answers are often shown as: net productivity = (gross) photosynthesis (minus) respiration. (iii). (Shade plant) has lower (rate of) respiration / respiratory losses / less CO released at 0 light intensity / in dark; Accept use of figures. Accept: lower compensation point.. Greater (net) productivity / less sugars / glucose used / more sugars / glucose available; Neutral: any references to rate of photosynthesis. [8] (i) Nitrification / oxidation; Accept nitrifying Denitrification; Accept denitrifying. (Nitrogen) to ammonia / NH 3 / ammonium;. Do not disqualify mark for any references to ammonia being converted to nitrite, nitrate etc. Produce protein / amino acids / named protein / DNA / RNA;. Do not disqualify mark for any references to protein being formed from nitrogen, nitrite or nitrate Page 56 of 85

57 (c). Soil has low(er) water potential / plant / roots have higher water potential;. Reference to water potential gradient is sufficient if correct direction of gradient or water movement is outlined. Accept WP or Ψ for water potential. Osmosis from plant / diffusion of water from plant;. Accept plant takes up less / not enough water by osmosis. Reference to movement of minerals by osmosis negates mark [6] 3 (i). Gases / correct named gas not released;. Conditions (in digester) can be controlled; 3. Products / named product can be collected; 4. Open ponds associated with health risk / environmental damage / eutrophication; Correct named gases include: methane, carbon dioxide, hydrogen sulphide, nitrogen oxides. Allow substance = product 4. Accept pond in any context max. Respiration causes temperature increase / release of heat;. Enzymes would be denatured / microorganisms killed; (i). Increase algae / algal bloom causes light to be blocked out;. Plants can t photosynthesise / plants and / or algae die; 3. Bacteria / saprobionts / EW feed off / breakdown dead organisms using up oxygen / bacteria respire / BOD rises; 3. Acts as soil conditioner / improves drainage / aerates soil / increases organic content of soil;. Contains other elements / named element / wider range of elements; 3. Production of artificial fertiliser energy-consuming; 4. Less leaching / slow release (of nutrient); Unspecified answers relate to natural fertiliser. Ignore references to cost / eutrophication. i.e. elements other than nitrogen, phosphorus and potassium max [8] Page 57 of 85

58 4 Complementary to / fits / binds to active site; Competitive / competes / prevents enzyme-substrate complexes / prevents urea attaching; Max one mark if candidate suggests that active site / enzyme is damaged destroyed or useless. Allow inhibitor prevents or stops urea / substrate attaching unless candidate clearly indicates this is permanent. Ignore reference to inhibitor forming an enzyme / substrate complex. (i) Reduces loss of ammonia up to day8 / 9; Increase in urease / temperature; More enzyme-substrate complexes; More bacteria; max (c) Less urea / ammonia lost (from soil) / less urea broken down; Urea / ammonia converted to nitrite / nitrate; Used to produce protein / amino acids / DNA / bases / nucleotides; Reference to incorrect bacteria (e.g. denitrifying) producing nitrite / nitrate negates second marking point. 3 [8] 5 Ammonia / ammonium / NH 3 / NH 4 + ; Will have similar shape / tertiary structure (as substrate) / complementary shape (to active site); Neutral: same shape as substrate Fit / bind with active site / forms enzyme-substrate complex; Reject: same shape as active site (c) (i) Provides ATP for the reaction / nitrogen fixation / reduction of nitrogen / formation of ammonia; Accept: ATP or energy Enzyme / nitrogenase produced quicker / more enzyme produced; Ignore references to temperature Uses / removes oxygen (so nitrogenase works); Use of oxygen must be in the correct context max Page 58 of 85

59 ATP used for / needed for nitrogen fixation / reduction of nitrogen / formation of ammonia / production of enzyme / nitrogenase; Accept: ATP or energy (So less ATP) available for growth / protein synthesis / production of new cells / production of biomass; Accept: converse for those without fertiliser [7] 6 (i) dissolve (in soil water) / run-off / leaching; reject nitrogen dissolving. insoluble / less soluble; (molecules) require breaking down / slow release; increased growth / algal bloom; blocks light; less photosynthesis; plants die; increase in decomposers / bacteria; ignore growth of bacteria bacteria respire; less oxygen; 4 max [7] 7 (i) decomposers convert (nitrogen in organic compounds) into ammonia / ammonium; suitable example of organic nitrogen - protein / urea / amino acid etc. (e.g. linked to process); nitrifying bacteria / correctly named convert ammonium to nitrate; via nitrite; 3 convert nitrogen (gas) into ammonium / ammonia / amino acids; add usable / available nitrogen to an ecosystem / eq.; (i). numbers of dispersed bacteria increase as they feed on organic matter;. numbers of free-swimming protoctistans increase because number of bacteria increase; 3. dispersed bacteria decrease as amount of dispersed organic matter decreases / due to lack of food / as organic matter is converted to flocs / are preyed on by free-swimming protoctistans; 3 Page 59 of 85

60 . (in a succession) organisms (enter an area and) change the environment / conditions creating new niches / habitats;. allows different species / different types of organisms to enter / be successful; 3. dispersed bacteria change dispersed organic matter to flocs; 4. presence of flocs allows crawling protoctistans to enter / to increase / to be successful; 4 [] 8 (i) (molecules) Cannot pass out of cell; Quickly / easily broken down (hydrolysed) / broken down in a on-step reaction / immediate source of energy; Stores / releases small amounts of energy; Do not credit producing energy max Formed when reduced NAD used to reduce / donate H ions to pyruvate / convert pyruvate to ethanol; [4] 9 P denitrification; Q Nitrogen fixation; Ammonia formed by decay / decomposition / putrefying / ammonifying / by action of decomposers / saprobionts; On nitrogenous waste / urea or nitrogenous compounds (e.g. proteins, amino acids, DNA, ATP); (c) Oxygen added / hydrogen removed; Ignore references to electron loss [5] 0 On diagram, correctly labelled: Light-dependent: granum / thylakoid membranes labelled X AND Light-independent: stroma labelled Y ; Page 60 of 85

61 Any two from: (Water) forms H + / hydrogen ions and electrons / e ; O / oxygen formed; [NOT O, NOT O ] (Light) excites electrons / raises energy level of electrons / electrons to chlorophyll / to photosystem; max (c) (ATP) Provides energy for GP TP / provides P for RuP / TP RuBP; (Reduced NADP) Provides H / electrons for GP TP / reduces GP to TP; [5] X = Carbon dioxide; Y = Acetyl coenzyme A; (ACCEPT Acetyl CoA) Z = Water; (i) Cytoplasm; 3 Mitochondrion; (IGNORE named part) (c) On the diagram: (i) A (ATP used) between glucose and triose phosphate; B Any two from: (ATP produced) between triose phosphate and pyruvate; in Krebs cycle; from electron carriers (to right of bracket & not below grey box); max Page 6 of 85

62 (d) Any three from: Source of energy / of phosphate; Active transport; Phagocytosis / endo- / exocytosis / pinocytosis; Bile production; Cell division / mitosis; Synthesis of: glycogen; protein / enzymes; DNA / RNA; lipid / cholesterol; urea; max 3 (e) Any four from: Forms lactate; [extras C H 5 OH / CO CANCEL] Use of reduced NAD / NADH; Regenerates NAD; NAD can be re-used to oxidise more respiratory substrate / correct e.g. / allows glycolysis to continue; Can still release energy / form ATP when oxygen in short supply / when no oxygen; max 4 [5] CO, water, ATP, reduced NAD / FAD; (accept creatine phosphate)(any - one tick) (i) build up / increased concentration of lactate lowers + ph / increases H / increases acidity; enzymes / named protein inhibited(not denatured); lactate / pyruvate is an energy source; muscles have increased / immediate energy or ATP supply; (accept lactate replenishes glycogen or glucose) restores ph levels; max [5] Page 6 of 85

63 3 (i) nitrogen-fixing; nitrifying; (names neutral, name only no mark) (i) growing legumes / named legume; ploughed in / allowed to decompose / nitrogen-fixing (bacteria in nodules); OR allow cattle / named species / (farm) animals (to graze); add dung / urine; OR spread / add manure / slurry; decomposed to release nitrates / ammonia / nitrites; bare soil / fallow in winter / hedge removal; leaching (of nitrates) / soil erosion; OR uptake of nitrates / ammonium compounds by crop; harvesting crop / named crop which would be harvested; OR (farm) animals eat plants (in field); (then) animals removed; [6] 4 lactate / lactic acid / pyruvate; ATP; (i) energy demand is very high / high respiration rate; unable to supply enough oxygen to muscles / tissues / cells / insufficient time for oxygen to reach muscles / tissues / cells / insufficient oxygen in muscles / tissues / cells; break down with oxygen / oxidise lactate into pyruvate / glucose / glycogen / CO + water; by aerobic respiration; [6] Page 63 of 85

64 5 matrix; pyruvate; ADP; P / inorganic phosphate; reduced NAD; oxygen; max (c) larger surface area for electron carrier system / oxidative phosphorylation; provide ATP / energy for contraction; [5] 6 transmission / reflected / misses chlorophyll / chloroplasts / wrong wavelength; (larger area) to absorb light; (larger surface area) to absorb carbon dioxide; short diffusion pathway for gases / oxygen / CO ; light able to penetrate to all cells; max (c) effect; detail; effect on photosynthesis; some effects are less light / light absorbed by water different wavelength of light temperature availability of carbon dioxide availability of water (more than one effect award mark only) 3 [6] 7 (i) ammonia / ammonium ions / compound; glucose; (c) (d) final acceptor for hydrogen: to form water; glycolysis can continue; NAD can accept more hydrogen; secondary / tertiary structure; produces particular shape of active site; or (shape of) active site; complementary to shape of substrate; Page 64 of 85

65 (e) sodium ions / non-competitive inhibitor binds to enzyme at a site other than active site; resulting in change of shape of active site / no longer complementary; substrate can no longer bind with the enzyme / enzyme-substrate complexes no longer formed; 3 [] 8 source of pests / animals, and effect on crop; source of weeds / no longer taking nutrients, hence competition / reduced yield; creation of larger fields / leaving room, hence more efficient use of machinery / grow more crops; hedgerows have to be maintained, so removal saves time / money; max allows beetles to remain / survive / over winter in the middle of the field / strip of grass; effect on distribution, e.g. do not normally reach the centre of the field / can reach all parts; (c) increases biodiversity; source of food for animals; habitat / nest for animals; reduce need for insecticides / attracts insects away from crop; windbreaks / prevent erosion / run-off / leaching; migratory corridors; max [6] 9 ( mark for three correct answers) ( marks for six correct answers) Page 65 of 85

66 reduced NAD / NADH / NADH ; reduced FAD / FADH / FADH ; ATP; 3 [5] 30 (i) RuBP 5; GP 3; TP 3; Glucose 6; (all correct = marks; 3 or correct = mark) (iii) (iv) stroma; light-dependent reaction / (photo)phosphorylation; (accept photolysis) 5 out of 6 / 83% / equivalent; enzymes involved / not a photochemical reaction; slow rate of enzyme / chemical reaction at low temperature / less kinetic energy / fewer collisions; [7] 3 (more cristae / larger surface area) for electron transport chain / more enzymes for ATP production / oxidative phosphorylation; muscle cells use more ATP (than skin cells)(not just more respiration); (i) pyruvate; carbon dioxide formed / decarboxylation; hydrogen released / reduced NAD formed; acetyl coenzyme A produced; max (c) NAD / FAD reduced / hydrogen attached to NAD / FAD; H + ions / electrons transferred from coenzyme to coenzyme / carrier to carrier / series of redox reactions; energy made available as electrons passed on; energy used to synthesise ATP from ADP and phosphate / using ATPase; H + / protons passed into intermembrane space; H + / protons flow back through stalked particles / enzyme; 3 max [8] Page 66 of 85

67 3 proteins / amino acids broken down; deamination / ammonification / release of ammonium compounds; conversion to nitrates; by nitrifying bacteria / named bacterium; nitrates absorbed into roots; 5 fewer nitrates in the soil for the next crop / plants grow less well because of lack of nitrates; requiring application of more fertiliser / economic reason for using less fertiliser / valid environmental reason explained e.g. nitrates leaching into water / eutrophication / explanation / health related e.g drinking water; (c) production of phospholipids; in cell membranes; synthesis of ATP; production of DNA; production of RNA; production of NADP; 4 max [] 33 (i) 9.47(9.5); ( marks for correct answer) 40% / 0.4 of 800 / 38; released as heat; (i) glucose only partly broken down / only broken down to lactate; lactate / lactic acid has built up / been produced; oxygen used to break down lactate / convert it back to pyruvate / glucose / glycogen; [6] 34 rate of photosynthesis increased; normal atmospheric concentration a limiting factor / more / faster production of biomass or sugars / more products of photosynthesis transported to fruits; Page 67 of 85

68 Accept oxygen/o (c) (increased temperature) increases rate of respiration; rate of photosynthesis too low to replace respiratory loss lower water potential of nutrient solution; less water absorbed into roots (by osmosis); (not: water lost from roots) [6] 35 (i) Reduced NADP; Accept NADPH/ NADPH + /NADPH ATP; (To incorporate carbon dioxide) to make sugars/glucose/fructose; Accept to fix carbon dioxide Accept correct biochemical answers Accept provide energy to make sugars Change (in CO exchange) due to photosynthesis; Plants carry out photosynthesis and respiration; At X (rates of) respiration and photosynthesis same; max [5] Page 68 of 85

69 Examiner reports In (i), most candidates scored one mark but about a quarter could not place glycolysis in the cytoplasm. In, only about half of candidates correctly referred to the inner membrane of the mitochondrion. Quite a large number made reference to chloroplasts, or parts of the chloroplast. This question proved a good discriminator. Nearly forty percent obtained all three marks but a third scored nothing. Many tried to include unnecessary and often incorrect details about the whole of aerobic respiration. The best answers focused on oxygen as the final electron acceptor of the electron transport chain, associated with oxidative phosphorylation (or described) which produces a lot of ATP. (c) Most candidates realised that substance X must be pyruvate, although some thought it was glucose and others suggested acetylcoenzyme A Again, most knew that this was the Krebs cycle, but all three other stages of aerobic respiration were suggested. Some answers here were disappointing and did not really get beyond a GCSE appreciation of aerobic respiration. Others saw the phrase production of ATP and gave a detailed account of reduction and oxidation along the electron transfer chain, often including the chemi-osmotic theory of ATP production. Those who read the question carefully realised that this wasn t required and confined themselves to describing the role of oxygen as the terminal electron acceptor, making possible the oxidation of reduced NAD. They explained that if this did not happen, the transfer of electrons along the electron transfer chain, with the associated production of ATP, would come to a halt. Page 69 of 85

70 3 (i) Almost 90% of students correctly identified the cytoplasm as where stage of anaerobic respiration occurs. Rather surprisingly, almost a third of students did not obtain either of the two marks available in this question. These students often focused on the importance of ATP being continually produced without any explanation of how stage would enable this to occur. Students obtaining both marks clearly explained that the regeneration of NAD in stage enabled NAD to be reduced again in stage. Many answers mentioned the regeneration of NAD but then only stated that this enabled glycolysis to continue. Common errors included confusion between oxidation and reduction, stage being identified as the link reaction and NAD being reduced by protons (without any mention of electrons). Only a minority of students referred to NADP instead of NAD. (i) Slightly more than half the students correctly calculated the RQ value for aerobic respiration of glucose as being one. The wide range of incorrect answers indicated that many students had limited knowledge of the equation for aerobic respiration of glucose. Two thirds of students gained at least one mark, often for stating that a greater volume of carbon dioxide was produced than oxygen used. Approximately one in five students gained a second mark by explaining that aerobic and anaerobic respiration were occurring. Students failing to gain any credit often suggested that the seeds were photosynthesising or that no oxygen was being used as only anaerobic respiration was occurring. (c) This was generally well answered with close to 90% of students obtaining at least one mark. Many students gained a mark for stating that, in anaerobic respiration ATP is only produced during glycolysis. A second mark was obtained by approximately 60% of students, usually by stating that aerobic respiration uses the electron transfer chain. Some answers also stated that oxygen is the terminal acceptor of the electron transfer chain. Page 70 of 85