Biology 0610 | Paper 4 Mock 01 | Theory (Extended)
Question 1 Report
The carbon cycle recycles carbon between the atmosphere, living organisms and the environment. Carbon moves between these stores as organisms feed, respire and die, and as fuels are burned. Fig. 1.1 is a diagram of the carbon cycle. Two of the processes are labelled A and B, and the diagram also shows plants, animals, decomposers and fossil fuels.
(a) State the name of the gas, present in the atmosphere, that is cycled in the carbon cycle. [1]
(b) Name the processes labelled A and B on Fig. 1.1. [2]
(c) Describe the part played by decomposers in returning carbon to the atmosphere. [3]
(d) Explain how the burning of fossil fuels can lead to an increase in the Earth's temperature. [4]
(e) State two ways, other than decomposition, by which carbon dioxide is added to the atmosphere. [2]
(f) Suggest two ways in which humans could reduce the amount of carbon dioxide released into the atmosphere. [2]
(a) The atmospheric gas cycled in the carbon cycle is carbon dioxide [1].
(b) The labelled processes are: A = photosynthesis (removes carbon dioxide from the air into plants) [1]; B = respiration (returns carbon dioxide to the air) [1].
(c) Decomposers return carbon to the air because decomposers (bacteria and fungi) feed on / break down dead organisms and waste [1]; as they do so they respire [1], which releases carbon dioxide back into the atmosphere [1].
(d) Burning fossil fuels can raise Earth's temperature because fossil fuels contain carbon (locked up from ancient organisms) [1]; combustion releases this as carbon dioxide [1]; carbon dioxide is a greenhouse gas that absorbs / traps heat re-radiated from the Earth's surface [1]; the resulting enhanced greenhouse effect raises the global temperature [1].
(e) Two ways, other than decomposition, that add carbon dioxide to the air: respiration (of plants and animals) [1]; combustion / burning of fuels [1].
(f) Two ways humans could reduce carbon dioxide released (1 each): burn less fossil fuel / use renewable energy sources [1]; plant more trees and reduce deforestation (so more CO2 is removed by photosynthesis) [1] (max 2).
Answer Details
(a) The atmospheric gas cycled in the carbon cycle is carbon dioxide [1].
(b) The labelled processes are: A = photosynthesis (removes carbon dioxide from the air into plants) [1]; B = respiration (returns carbon dioxide to the air) [1].
(c) Decomposers return carbon to the air because decomposers (bacteria and fungi) feed on / break down dead organisms and waste [1]; as they do so they respire [1], which releases carbon dioxide back into the atmosphere [1].
(d) Burning fossil fuels can raise Earth's temperature because fossil fuels contain carbon (locked up from ancient organisms) [1]; combustion releases this as carbon dioxide [1]; carbon dioxide is a greenhouse gas that absorbs / traps heat re-radiated from the Earth's surface [1]; the resulting enhanced greenhouse effect raises the global temperature [1].
(e) Two ways, other than decomposition, that add carbon dioxide to the air: respiration (of plants and animals) [1]; combustion / burning of fuels [1].
(f) Two ways humans could reduce carbon dioxide released (1 each): burn less fossil fuel / use renewable energy sources [1]; plant more trees and reduce deforestation (so more CO2 is removed by photosynthesis) [1] (max 2).
Question 2 Report
Fig. 6.1 shows the human male reproductive system as seen from the side. Sperm cells are produced continuously in the testes from the time a boy reaches puberty. The sperm cells then pass along a series of tubes, mixing with fluids released by several glands to form semen, before they leave the body. The letters P, Q, R and S label four structures involved in the production and release of sperm cells.
(a) Using Fig. 6.1, name the structure labelled P in which the sperm cells are made. [1]
(b) State the letter, from Fig. 6.1, of the tube along which sperm cells pass on their way out of the body. [1]
(c) Describe two ways in which the testes are adapted for the continuous production of large numbers of sperm cells. [2]
(d) Explain why sperm cells need the sugary fluid that is added to them by the glands to form semen. [3]
(e) Explain the advantages to a species of producing offspring by sexual reproduction rather than by asexual reproduction. [3]
This question refers to Fig. 6.1, a side view of the male reproductive system with structures labelled P, Q, R and S; the answers below follow the standard anatomy of that system.
(a) Structure P, where the sperm cells are made, is the testis (testes) [1]. Sperm are produced continuously in the seminiferous tubules of the testis from puberty.
(b) The tube along which sperm pass on their way out of the body is S (the sperm duct leading to the urethra) [1].
(c) Two adaptations of the testes for continuous production of large numbers of sperm (1 each): they contain many coiled seminiferous tubules, giving a large surface area for sperm production [1]; and they are held outside the body in the scrotum, at a slightly lower temperature that is best suited to sperm production [1].
(d) Sperm need the sugary fluid because the sugar (fructose) provides energy for respiration [1]; this respiration takes place in the many mitochondria in the middle piece of the sperm [1]; the energy released is used to move the tail (flagellum) so the sperm can swim to the egg [1].
(e) The advantage of sexual over asexual reproduction is that it produces genetic variation in the offspring [1], because genes come from two parents when gametes fuse at fertilisation [1]; this variation means the species is more likely to have some individuals that survive a change in the environment or a new disease [1].
Answer Details
This question refers to Fig. 6.1, a side view of the male reproductive system with structures labelled P, Q, R and S; the answers below follow the standard anatomy of that system.
(a) Structure P, where the sperm cells are made, is the testis (testes) [1]. Sperm are produced continuously in the seminiferous tubules of the testis from puberty.
(b) The tube along which sperm pass on their way out of the body is S (the sperm duct leading to the urethra) [1].
(c) Two adaptations of the testes for continuous production of large numbers of sperm (1 each): they contain many coiled seminiferous tubules, giving a large surface area for sperm production [1]; and they are held outside the body in the scrotum, at a slightly lower temperature that is best suited to sperm production [1].
(d) Sperm need the sugary fluid because the sugar (fructose) provides energy for respiration [1]; this respiration takes place in the many mitochondria in the middle piece of the sperm [1]; the energy released is used to move the tail (flagellum) so the sperm can swim to the egg [1].
(e) The advantage of sexual over asexual reproduction is that it produces genetic variation in the offspring [1], because genes come from two parents when gametes fuse at fertilisation [1]; this variation means the species is more likely to have some individuals that survive a change in the environment or a new disease [1].
Question 3 Report
| Temperature / °C | Time for film to clear / s |
|---|---|
| 20 | 150 |
| 30 | 80 |
| 40 | 35 |
| 50 | 90 |
| 60 | 210 |
| 70 | did not clear |
Fig. 4.1
Protease enzymes digest protein. A food scientist investigated a protease used in a washing powder by placing squares of exposed photographic film, which are coated in protein, into the enzyme at different temperatures. The time for the protein coating to clear from the film was measured. Fig. 4.1 shows the results.
(a) State the name of the products formed when protein is digested by a protease. [1]
(b) State the temperature at which the protease worked fastest. [1]
(c) Describe how the rate of the reaction changes as temperature increases from 20 °C to 70 °C. [3]
(d) Explain why the film did not clear at all at 70 °C. [3]
(e) Suggest why this protease is useful in a washing powder. [2]
(f) Complete the sentence: an enzyme is described as .......... because each type only acts on one type of substrate. [1]
(g) Describe how you would show that a solution contains protein. [3]
This question tests enzyme action, the effect of temperature including denaturation, and the biuret food test.
(a) When a protease digests protein the products are amino acids [1].
(b) The protease worked fastest at 40 °C [1] (the optimum temperature, where clearing time was shortest).
(c) Describe the change from 20 to 70 °C [3]: from 20 to 40 °C the rate increases (the clearing time falls) [1]; the rate is fastest at the optimum, 40 °C [1]; above 40 °C the rate decreases and the film takes longer to clear or does not clear [1]. Below the optimum, more heat gives molecules more kinetic energy and more successful collisions; above it, denaturation takes over.
(d) No clearing at 70 °C because the enzyme is denatured [1]; the high temperature permanently changes the shape of the active site [1]; so the substrate can no longer bind and no digestion of the protein occurs [1]. Denaturation is permanent, which is why the film never clears rather than just clearing slowly.
(e) The protease is useful in washing powder because it removes protein stains such as blood, egg or food [1], and it works without needing a high temperature, so washing at lower temperatures saves energy [1].
(f) The missing word is specific [1] - each enzyme acts on only one type of substrate because its active site fits only that substrate.
(g) The test for protein [3]: add biuret solution (sodium hydroxide followed by copper sulfate) [1]; mix [1]; a positive result turns the solution purple/violet (it stays blue if no protein is present) [1].
Answer Details
This question tests enzyme action, the effect of temperature including denaturation, and the biuret food test.
(a) When a protease digests protein the products are amino acids [1].
(b) The protease worked fastest at 40 °C [1] (the optimum temperature, where clearing time was shortest).
(c) Describe the change from 20 to 70 °C [3]: from 20 to 40 °C the rate increases (the clearing time falls) [1]; the rate is fastest at the optimum, 40 °C [1]; above 40 °C the rate decreases and the film takes longer to clear or does not clear [1]. Below the optimum, more heat gives molecules more kinetic energy and more successful collisions; above it, denaturation takes over.
(d) No clearing at 70 °C because the enzyme is denatured [1]; the high temperature permanently changes the shape of the active site [1]; so the substrate can no longer bind and no digestion of the protein occurs [1]. Denaturation is permanent, which is why the film never clears rather than just clearing slowly.
(e) The protease is useful in washing powder because it removes protein stains such as blood, egg or food [1], and it works without needing a high temperature, so washing at lower temperatures saves energy [1].
(f) The missing word is specific [1] - each enzyme acts on only one type of substrate because its active site fits only that substrate.
(g) The test for protein [3]: add biuret solution (sodium hydroxide followed by copper sulfate) [1]; mix [1]; a positive result turns the solution purple/violet (it stays blue if no protein is present) [1].
Question 4 Report
Farmers add fertilisers to their fields. Fertilisers help crops to grow. They hold nitrates and other minerals. Plants need these to grow. When it rains, some fertiliser is washed away. It runs into rivers and lakes. The extra nitrate makes algae grow fast. The algae form a thick green layer on the water. This causes big problems for other living things. In some lakes many fish and animals die. This whole process is called eutrophication. A student was asked to explain the steps. The steps go from fertiliser entering a lake to the death of the fish.
(a) Name the substance in fertiliser that causes the algae to grow quickly. [1]
(b) Explain why the rapid growth of algae over the surface of the water causes the water plants below to die. [3]
(c) Explain how the death of the water plants and algae leads to a fall in the amount of oxygen in the water. [3]
(d) Explain why the fall in the amount of dissolved oxygen causes the fish to die. [2]
(e) Suggest two ways in which a farmer could reduce this type of water pollution. [2]
This question tests the sequence of eutrophication, from fertiliser reaching a lake to the death of the fish. The graph shows dissolved oxygen dropping just downstream of the nutrient input before recovering.
(a) The substance in fertiliser that makes the algae grow quickly is nitrate [1] (accept phosphate).
(b) Rapid algal growth kills the water plants below because the algae form a thick layer over the surface of the water [1]; this blocks the light from reaching the plants below [1]; so the plants cannot photosynthesise and they die [1].
(c) The dead plants and algae lower the oxygen because they are broken down by decomposers / bacteria [1]; the number of these bacteria increases greatly [1]; and they use up the dissolved oxygen in the water for their own respiration [1].
(d) The fall in dissolved oxygen kills the fish because there is not enough dissolved oxygen for the fish to respire [1]; so the fish suffocate and die [1].
(e) Any two ways a farmer could reduce this pollution (1 each): use less fertiliser; do not spread fertiliser near rivers; do not spread fertiliser just before heavy rain; or leave a buffer strip of plants along the river to absorb run-off [2].
Answer Details
This question tests the sequence of eutrophication, from fertiliser reaching a lake to the death of the fish. The graph shows dissolved oxygen dropping just downstream of the nutrient input before recovering.
(a) The substance in fertiliser that makes the algae grow quickly is nitrate [1] (accept phosphate).
(b) Rapid algal growth kills the water plants below because the algae form a thick layer over the surface of the water [1]; this blocks the light from reaching the plants below [1]; so the plants cannot photosynthesise and they die [1].
(c) The dead plants and algae lower the oxygen because they are broken down by decomposers / bacteria [1]; the number of these bacteria increases greatly [1]; and they use up the dissolved oxygen in the water for their own respiration [1].
(d) The fall in dissolved oxygen kills the fish because there is not enough dissolved oxygen for the fish to respire [1]; so the fish suffocate and die [1].
(e) Any two ways a farmer could reduce this pollution (1 each): use less fertiliser; do not spread fertiliser near rivers; do not spread fertiliser just before heavy rain; or leave a buffer strip of plants along the river to absorb run-off [2].
Question 5 Report
Cells need energy to stay alive. They release it from food in respiration. The food is mostly glucose. Usually this uses oxygen. This is called aerobic respiration. Sometimes there is not enough oxygen. Then cells release energy without it. This is anaerobic respiration. During hard exercise the muscles cannot get oxygen fast enough. So they respire without oxygen for a time. This releases energy. But it also makes lactic acid. The acid builds up in the muscles. It makes them ache and tire. Yeast can respire this way too. A student had just finished a sprint. They were asked why their muscles ached.
(a) Write the word equation for anaerobic respiration in human muscle. [2]
(b) Explain why the muscles respire anaerobically during hard exercise. [2]
(c) Explain why anaerobic respiration releases less energy from each glucose molecule than aerobic respiration. [2]
(d) Explain why the athlete continues to breathe deeply and quickly for some time after the exercise has stopped. [3]
(e) State the products of anaerobic respiration in yeast. [1]
This question is about anaerobic respiration in exercising muscle: why it happens, its lower energy yield, and the oxygen debt repaid afterwards.
(a) The word equation for anaerobic respiration in human muscle:
glucose \(\rightarrow\) lactic acid [1] (+ energy released) [1].
Note that no oxygen is used and no carbon dioxide or water is produced, unlike aerobic respiration.
(b) During hard exercise the muscles respire anaerobically because oxygen cannot be delivered to the muscles fast enough to meet demand [1], so the muscles release energy without oxygen (anaerobically) to keep contracting [1].
(c) Anaerobic respiration releases less energy per glucose molecule because the glucose is not completely broken down [1] (it is only partly broken down to lactic acid), so less energy is released than when glucose is fully broken down using oxygen to carbon dioxide and water [1].
(d) After exercise the athlete keeps breathing deeply and quickly because lactic acid has built up in the muscles, creating an oxygen debt [1]; extra oxygen is needed to break down (oxidise) this lactic acid [1]; so the deep, fast breathing continues to supply that extra oxygen until the debt is repaid [1].
(e) The products of anaerobic respiration in yeast are ethanol (alcohol) and carbon dioxide [1].
Answer Details
This question is about anaerobic respiration in exercising muscle: why it happens, its lower energy yield, and the oxygen debt repaid afterwards.
(a) The word equation for anaerobic respiration in human muscle:
glucose \(\rightarrow\) lactic acid [1] (+ energy released) [1].
Note that no oxygen is used and no carbon dioxide or water is produced, unlike aerobic respiration.
(b) During hard exercise the muscles respire anaerobically because oxygen cannot be delivered to the muscles fast enough to meet demand [1], so the muscles release energy without oxygen (anaerobically) to keep contracting [1].
(c) Anaerobic respiration releases less energy per glucose molecule because the glucose is not completely broken down [1] (it is only partly broken down to lactic acid), so less energy is released than when glucose is fully broken down using oxygen to carbon dioxide and water [1].
(d) After exercise the athlete keeps breathing deeply and quickly because lactic acid has built up in the muscles, creating an oxygen debt [1]; extra oxygen is needed to break down (oxidise) this lactic acid [1]; so the deep, fast breathing continues to supply that extra oxygen until the debt is repaid [1].
(e) The products of anaerobic respiration in yeast are ethanol (alcohol) and carbon dioxide [1].
Question 6 Report
Fig. 16.1
Fig. 16.1 shows a food web in a woodland community that contains an oak tree, several insects, some small birds and a bird of prey. The arrows show the direction in which energy flows between the organisms as one organism is eaten by another.
(a) State what the arrows in a food web represent. [1]
(b) State the name given to the oak tree in this food web. [1]
(c) Name one organism that is a secondary consumer in this food web. [1]
(d) Describe and explain what would happen to the number of caterpillars if all the blue tits were removed from the woodland. [3]
(e) Explain why a food web is a better model of feeding relationships than a single food chain. [2]
(f) Explain the role of the fungi in returning nutrients to the woodland. [3]
(g) Suggest one effect on the food web if a disease killed most of the oak trees. [2]
This question is about interpreting a food web (energy flow, trophic levels) and the effects of removing organisms. Note: the question text and mark scheme describe a woodland web (oak tree, caterpillars, blue tits, ladybirds, bird of prey); answer in those terms. If the displayed diagram shows different (marine) organisms, that appears to be a figure mismatch and should be checked by a reviewer.
(a) The arrows represent the direction of energy flow, that is the transfer of energy from one organism to the organism that eats it [1].
(b) The oak tree is a producer [1], because it makes its own food by photosynthesis and is the starting point of the food web.
(c) Any organism that eats a primary consumer is a secondary consumer, for example a blue tit or a ladybird [1] (it feeds on the caterpillars/aphids that ate the plant).
(d) If all the blue tits were removed, the number of caterpillars would increase [1]; because one of their predators has been removed [1]; so fewer caterpillars are eaten and more survive to reproduce [1] [3]. (Over time the increase may be limited as their food plants are eaten up.)
(e) A food web is a better model than a single food chain because it shows that an organism may have more than one food source and more than one predator [1]; so it represents the real, interconnected feeding relationships of the whole community more accurately [1] [2].
(f) The fungi are decomposers [1]; they break down dead organisms and waste material [1]; releasing mineral ions / nutrients back into the soil for plants to absorb [1] [3]. This recycles nutrients so producers can keep growing.
(g) If a disease killed most of the oak trees, any sensible linked effect (max 2): the caterpillars and aphids lose their food source, so their numbers decrease [1]; and this reduces the food available for their predators, so the numbers of blue tits / ladybirds also fall [1] [2].
Answer Details
This question is about interpreting a food web (energy flow, trophic levels) and the effects of removing organisms. Note: the question text and mark scheme describe a woodland web (oak tree, caterpillars, blue tits, ladybirds, bird of prey); answer in those terms. If the displayed diagram shows different (marine) organisms, that appears to be a figure mismatch and should be checked by a reviewer.
(a) The arrows represent the direction of energy flow, that is the transfer of energy from one organism to the organism that eats it [1].
(b) The oak tree is a producer [1], because it makes its own food by photosynthesis and is the starting point of the food web.
(c) Any organism that eats a primary consumer is a secondary consumer, for example a blue tit or a ladybird [1] (it feeds on the caterpillars/aphids that ate the plant).
(d) If all the blue tits were removed, the number of caterpillars would increase [1]; because one of their predators has been removed [1]; so fewer caterpillars are eaten and more survive to reproduce [1] [3]. (Over time the increase may be limited as their food plants are eaten up.)
(e) A food web is a better model than a single food chain because it shows that an organism may have more than one food source and more than one predator [1]; so it represents the real, interconnected feeding relationships of the whole community more accurately [1] [2].
(f) The fungi are decomposers [1]; they break down dead organisms and waste material [1]; releasing mineral ions / nutrients back into the soil for plants to absorb [1] [3]. This recycles nutrients so producers can keep growing.
(g) If a disease killed most of the oak trees, any sensible linked effect (max 2): the caterpillars and aphids lose their food source, so their numbers decrease [1]; and this reduces the food available for their predators, so the numbers of blue tits / ladybirds also fall [1] [2].
