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Unit 4: Populations and the environment Chapters: 1 – Populations 2 – ATP 3 – Photosynthesis 4 – Respiration 5 – Energy and ecosystems 6 – Nutrients cycles 7 – Ecological succession 8 – Inheritance and selection Exam dates: Friday 11th January 2013 – PM Tuesday 11th June 2013 – AM Length: 1 hour and 30 minutes Total marks: 75 Percentage of A2: 16.7% Unit introduction: Living organisms form structured communities within dynamic but essentially stable ecosystems through which energy is transferred and chemical elements are cycled. Humans are part of the ecological balance and their activities affect it both directly and indirectly. Consideration of these effects underpins the content of this unit and should lead to an understanding that sustainability of resources depends on effective management of the conflict between human needs and conservation. Unit 4: Chapter 1: Populations 1.1 Populations and ecosystems: Key words: What is meant by the terms ‘environment’, ‘biotic’, ‘abiotic’ and ‘biosphere’? What is an ecosystem? What is meant by the terms ‘population’, ‘community’ and ‘habitat’? What is a niche? ecology, abiotic, biotic, biosphere, ecosystem, population, niche, community, habitat, microhabitat Explain what is meant by the term ecology: Explain what is meant by the term community: Explain what is meant by the term ecosystem: Explain what is meant by the term habitat: Explain what is meant by the term populations: Explain what is meant by the term ecological niche: Unit 4: Chapter 1: Populations 1.2 Investigating populations: Key words: What factors should be considered when using a quadrat? How is a transect used to obtain quantitative data about changes in communities along a line? How is the abundance of different species measured? How can the mark-release recapture method be used to measure the abundance of mobile species? habitat, abundance, quadrat, sample, random, transect, frequency, percentage cover, mark-releaserecapture, analysis Explain the factors that should be considered when using a quadrat: Explain how you would measure abundance: Explain what is meant by the term random sampling, and how you would ensure that a sample is truly random: Explain what mark-release-recapture is and how it is used to estimate population size: Explain how you wold sample along a transect: Explain how you would analyse the data: Unit 4: Chapter 1: Populations 1.3 Variation in population size: Key words: What factors determine the size of a population? Which abiotic factors affect the size of a population? How does each of these factors affect population size? population, population growth curve, limiting factors, abiotic, biotic, pH, temperature, light, water, humidity Explain what factors affect the size of a given population: Explain how the following factors affect population size: pH: light: Label and explain the stages of the population growth curve: temperature: water and humidity: Unit 4: Chapter 1: Populations 1.4 Competition: Key words: What is intraspecific competition? What factors do different species compete for? What is interspecific competition? How does interspecific competition influence population size? competition, intraspecific, intraspecific, population, niche, Explain what intraspecific competition is: Explain what interspecific completion is, in your answer include information on the factors different species complete for: Explain how interspecific competition influences population size: Unit 4: Chapter 1: Populations 1.5 Predation: Key words: What is predation? How does the predator-prey relationship affect the population size of the predator and the prey? predator, prey, predation, population, ecosystem, selection pressure Explain what predation is: Explain what is happening in this graph: Explain the effect predator-prey relationships have on population size: Explain what is happening in this graph: Unit 4: Chapter 1: Populations 1.6 Human populations: Key words: How does the human population growth curve differ from that of most other organisms? What factors affect the growth and size of human populations? migration, emigration, immigration, birth rate, death rate, survival, life expectancy Explain how the following factors that affect human population, and how they are calculated: Migration: Use the graphs to help you explain: Stable population: Birth rate: Increasing population: Death rate: Decreasing population: Unit 4: Chapter 1: Populations Exam questions Blue tits are small birds that live in woods. An ecologist estimated the size of the blue tit population visiting gardens near a wood in November. • She trapped 28 blue tits. She marked all of these birds with small metal rings on their legs. • Two weeks later, she trapped another sample of blue tits. Of these birds, 18 were marked and 20 were not marked. Use the data to estimate the size of the blue tit population. Show your working. Size of population .................................... (2 marks) The diagram shows some features of blue tit behaviour at different times of the year. Using mark-release-recapture to estimate the size of a blue tit population in June would not give reliable results. Explain why. (2 marks) Using mark-release-recapture to estimate the size of a blue tit population in March would not give reliable results. Explain why. (2 marks) Whales spend most of their time deep in the sea but they come to the surface to breathe. When they are at the surface, scientists obtain small samples of their skin. The scientists find the base sequence in some of the DNA from these samples. The base sequence is different in each whale. You could use the information about the base sequence to estimate the size of the whale population by using mark-release-recapture. Explain why. (2 marks) Unit 4: Chapter 1: Populations Exam questions Explain what is meant by the ecological term population. (1 mark) Four factors may affect the size of a human population. They are • Birth rate (B) • Death rate (D) • Emigration rate (E) • Immigration rate (I). Use all the letters B, D, E and I to write a formula showing a population that stays the same size The table shows some features relating to the human population of Mexico in 2007. In 1990 the life expectancy was 70 years. Suggest one reason for the change in life expectancy since 1990. (1 mark) Use the information in the table to calculate the size of the population of Mexico in 2008. Show your working. (1 mark) a population that is increasing in size. Answer ..................................................... (1 mark) (2 marks) Unit 4: Chapter 1: Populations Exam questions Parasites are organisms that live on or in host organisms. The populations of many organisms may be reduced by the effects of parasites. Feather mites are small parasites found on the wing feathers of many birds. The mites feed on the oil that the birds produce. This oil keeps the feathers in good condition. Birds unable to oil their feathers properly use more energy in maintaining their body temperature. This results in less energy being available for other processes. Scientists investigated the relationship between the numbers of feather mites and the breeding success of one species of bird, the great tit. Use the information above to suggest how feather mites could affect breeding in great tits. The scientists calculated the percentage of each pair’s eggs from which chicks survived to leave the nest. They called this ‘breeding success per pair’. The table shows some of the data that the scientists obtained. Do these data support the hypothesis that the presence of feather mites reduces the ability of great tits to reproduce successfully? Give reasons for your answer. (2 marks) The scientists located a large number of great tit nests. They sampled these at random. For each nest they recorded • the total number of eggs laid • the number of chicks that hatched from the eggs • the number of chicks that survived to leave the nest • the total number of feather mites on the two parent birds. Explain why the scientists sampled the nests at random. (2 marks) (3 marks) Unit 4: Chapter 1: Populations Exam questions The scientists calculated a correlation coefficient for these data. State a null hypothesis that would be appropriate for this investigation. Describe the relationship between the number of feather mites present on each great tit and the size of the oil gland. (1 mark) The correlation coefficient that they obtained had a negative value. What does a negative value indicate about these data? (1 mark) The oil that a great tit puts on its feathers is made in an oil gland at the base of the tail. The bird uses its beak to spread the oil over its feathers. This is called preening. Preening takes place in early morning and evening and empties the oil gland each time. After preening, the oil gland is considerably smaller. At the same time that the scientists recorded the number of feather mites on each great tit, they also measured the size of the oil gland. The graph shows their results and includes the scientist’s line of best fit. (2 marks) Explain how measuring the oil gland at the same time as counting the feather mites may have affected the reliability of the data. (2 marks) Feather mites eat pathogenic bacteria and fungi as well as oil. Explain how this may affect the breeding success of the birds. (2 marks) Unit 4: Chapter 2: ATP 2.1 Energy and ATP: Key words: What is energy and why do organisms need it? How does ATP store energy? How is ATP synthesised? What is the role of ATP in biological processes? State what energy is: Describe how ATP stores energy: State why organisms need energy: Explain how ATP is synthesised: Explain the role of ATP in biological processes Unit 4: Chapter 2: ATP Exam questions 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. (3 marks) 1 (b) Write a simple equation to show how ATP is synthesised from ADP. (1 mark) 1 (c) Give two ways in which the properties of ATP make it a suitable source of energy in biological processes. 1 2 (2 marks) Unit 4: Chapter 3: Photosynthesis 3.1 Overview of photosynthesis: Key words: How is the plant leaf adapted to carry out photosynthesis? What are the main stages of photosynthesis? ATP, photosynthesis, cuticle, light-dependent reaction, protons, electrons, NADP, grana, thylakoids, lamellae, stroma, chloroplasts Label the diagram to explain how a plant leaf is adapted to carry out photosynthesis and the main stages of photosynthesis: Unit 4: Chapter 3: Photosynthesis 3.2 The light-dependent reaction: Key words: What are oxidation and reduction? How is ATP made during the light-dependent reaction? What is the role of photolysis in the light-dependent reaction? How are chloroplasts adapted to carry out the light-dependent reaction? ATP, photolysis, oxidation, reduction, electrons, chlorophyll, thylakoids, Describe oxidation and reduction: Explain how ATP is made: Explain photolysis: Describe how chloroplasts are adapted to carry out the light-dependent reaction: Unit 4: Chapter 3: Photosynthesis 3.3 The light-independent reaction: Key words: How is carbon dioxide absorbed by plants incorporated into organic molecules? What are the roles of ATP and reduced NADP in the light-independent reaction? What is the Calvin cycle? ATP, NADP, Calvin cycle, stomata, stroma, Explain the steps of the Calvin cycle: Describe where the lightindependent reaction takes place: Explain the link between the Calvin cycle and the light-dependent reaction: Describe the lollipop experiment: Unit 4: Chapter 3: Photosynthesis 3.4 Factors affecting photosynthesis: Key words: What is meant by the concept of limiting factors? How can photosynthesis be measured? How do temperature, carbon dioxide concentration and light intensity affect the rate of photosynthesis? light-intensity, carbon dioxide, temperature, limiting factor, photosynthesis Explain how light intensity can affect the rate of photosynthesis: Explain how carbon dioxide concentration can affect the rate of photosynthesis: Explain how temperature can affect the rate of photosynthesis: Explain the law of limiting factors: Unit 4: Chapter 3: Photosynthesis Exam questions Scientists investigated the effects of temperature and light intensity on the rate of photosynthesis in creeping azalea. They investigated the effect of temperature on the net rate of photosynthesis at three different light intensities. They also investigated the effect of temperature on the rate of respiration. The graph shows the results. Use information from the graph to find the gross rate of photosynthesis at 20°C and medium light intensity. Answer ..................................................... (1 mark) Creeping azalea is a plant which grows on mountains. Scientists predict that in the area where this plant grows the mean summer temperature is likely to rise from 20°C to 23°C. It is also likely to become much cloudier. Describe and explain how these changes are likely to affect the growth of creeping azalea. Name the factors that limited the rate of photosynthesis between X and Y. (1 mark) Use information from the graph to explain your answer. (2 marks) (3 marks) Unit 4: Chapter 3: Photosynthesis Exam questions During photosynthesis, carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3phosphate (GP). This reaction is catalysed by the enzyme Rubisco. Rubisco can also catalyse a reaction between RuBP and oxygen to form one molecule of GP and one molecule of phosphoglycolate. Both the reactions catalysed by Rubisco are shown in Figure 1. Where exactly in a cell is the enzyme Rubisco found? (1 mark) Use the information provided to give the number of carbon atoms in one molecule of phosphoglycolate. Use Figure 1 to explain the results obtained in Figure 2. (2 marks) Use the information provided and your knowledge of the light-independent reaction to explain why the yield from soya bean plants is decreased at higher concentrations of oxygen. Phosphoglycolate is not used in the lightindependent reaction. (1 mark) Scientists investigated the effect of different concentrations of oxygen on the rate of absorption of carbon dioxide by leaves of soya bean plants. Their results are shown in Figure 2. (3 marks) Unit 4: Chapter 4: Respiration 4.1 Glycolysis: Key words: Where does glycolysis fit into the overall process of respiration? What are the main stages of glycolysis? What are the products of glycolysis? hydrolysis; activation energy; glycolysis State where glycolysis fits in the overall process of respiration: Describe the stages of glycolysis: 1) 2) 3) 4) State the products of glycolysis: Unit 4: Chapter 4: Respiration 4.2 Link reactions and the Krebs cycle: Key words: What is the link reaction? What happens during the Kerbs cycle? What are hydrogen carrier molecules and what is their role in the Krebs cycle? oxidised; eukaryotic cells; glycolysis; substrate-level phosphorylation; Explain the link reaction: Explain what happens in the Krebs cycle: Name the coenzymes and state why they are important: Explain the significance of the Krebs cycle: Unit 4: Chapter 4: Respiration 4.3 Electron transport chain: Key words: Where does the electron transport chain take place? How is ATP synthesised in the electron transport chain? What is the role of oxygen in aerobic respiration? aerobic; electrons; adenosine triphosphate; eukaryotic cells; protons; oxidation-reduction Describe the role of the mitochondria in respiration: Explain how ATP is synthesised in the electron transport chain: Describe the role of oxygen in aerobic respiration: Unit 4: Chapter 4: Respiration 4.4 Anaerobic respiration: Key words: How is energy released by respiration in the absence of oxygen? How is ethanol produced by anaerobic respiration? How is lactate produced by anaerobic respiration? glycolysis; Krebs cycle; Explain how energy is released by anaerobic respiration: Describe the production of lactate in animals: Describe the production of ethanol by plants and microorganisms: Compare the energy yields from aerobic and anaerobic respiration: Unit 4: Chapter 4: Respiration Exam questions The biochemical pathway of aerobic respiration involves an number of different steps. Name one step in which carbon dioxide is produced When the apple slices were transferred to nitrogen, the following biochemical pathway took place: (1 mark) In an investigation, scientists transferred slices of apple from air to anaerobic conditions in pure nitrogen gas. They measured the rate of carbon dioxide production. The scientists kept the temperature constant throughout the investigation. Explain how a decrease in temperature would affect the rate of carbon dioxide production. Use this pathway to explain the part played by reduced NAD when the apple slices were transferred to nitrogen (2 marks) (2 marks) The rate of carbon dioxide production was higher when the apple slices were in nitrogen than when they were in the air. Explain why. (3 marks) Unit 4: Chapter 4: Respiration Exam questions A student measured the rate of aerobic respiration of a woodlouse using the apparatus shown in the diagram. What measurements should the student have taken to calculate the rate of aerobic respiration in mm3 of oxygen g–1 h–1? The student closed the tap. After thirty minutes the drop of coloured liquid had moved to the left. Explain why the drop of coloured liquid moved to the left. (3 marks) DNP inhibits respiration by preventing a proton gradient being maintained across membranes. When DNP was added to isolated mitochondria the following changes were observed • less ATP was produced • more heat was produced • the uptake of oxygen remained constant. Explain how DNP caused these changes. (3 marks) (3 marks) Unit 4: Chapter 4: Respiration Exam questions Yeast is a single-celled organism. A student investigated respiration in a population of yeast growing in a sealed container. His results are shown in the graph. Use the information provided to explain the changes in production of ethanol during this investigation. (2 marks) Sodium azide is a substance that inhibits the electron transport chain in respiration. The student repeated the investigation but added sodium azide after 4 hours. Suggest and explain how the addition of sodium azide would affect oxygen uptake and the production of ethanol. Calculate the rate of oxygen uptake in arbitrary units per hour between 2 and 4 hours. Answer ...................................... arbitrary units per hour (1 mark) Use the information provided to explain the changes in oxygen uptake during this investigation. (3 marks) (3 marks) Unit 4: Chapter 5: Energy and ecosystems 5.1 Food chains and food webs: Key words: How does energy enter an ecosystem? How is energy transferred between the organisms in the ecosystem? What is meant by the terms ‘trophic level’, ‘food chain’, ‘food web’; ‘producer’, ‘consumer’ and ‘decomposer’? How is energy lost from the ecosystem? producers; consumers; decomposers; trophic level; food chain; food web; habitat; detritivores Explain the following terms: Trophic level: Describe how energy enters an ecosystem: Food chain: Food web: Describe how energy is transferred between organisms in an ecosystem: Producer: Consumer: Describe how energy is lost from the ecosystem: Decomposer: Unit 4: Chapter 5: Energy and ecosystems 5.2 Energy transfer between trophic levels: Key words: What percentage of energy is transferred from one trophic level to the next? How is energy lost along the food chain? Why do most food chains have no more than five trophic levels? How is the percentage efficiency of energy transfers calculated? ecosystem; net production; energy transfer; percentage efficiency; Using the diagram, explain: What percentage of energy is transferred from one trophic level to the next: How energy is lost along the food chain: Why most food chains have no more than five trophic levels: The efficiency of energy transfers is calculated using the following equation: 𝑒𝑛𝑒𝑟𝑔𝑦 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 = 𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑣𝑎𝑙𝑖𝑎𝑏𝑙𝑒 𝑎𝑓𝑡𝑒𝑟 𝑡ℎ𝑒 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 × 100 𝑒𝑛𝑒𝑟𝑔𝑦 𝑎𝑣𝑎𝑙𝑖𝑎𝑏𝑙𝑒 𝑏𝑒𝑓𝑜𝑟𝑒 𝑡ℎ𝑒 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟 Calculate the energy efficiency for this example: Energy available after the transfer = 50kJm-2year-1 Energy available before the transfer = 250kJm-2year-1 Unit 4: Chapter 5: Energy and ecosystems 5.3 Ecological pyramids: Key words: What are the different types of ecological pyramid? What are the relative merits and disadvantages of each? pyramid of numbers; pyramid of energy; pyramid of biomass Explain what a pyramid of numbers is: Explain what a pyramid of biomass is: Explain what a pyramid of energy is: Explain the advantages of using a pyramid of numbers: Explain the advantages of using a pyramid of biomass: Explain the advantages of using a pyramid of energy: Explain the disadvantages of using a pyramid of numbers: Explain the disadvantages of using a pyramid of biomass: Explain the disadvantages of using a pyramid of energy: Unit 4: Chapter 5: Energy and ecosystems 5.4 Agricultural ecosystems: Key words: What is an agricultural ecosystem? How do natural and agricultural ecosystems differ? What is meant by productivity? How is productivity calculated? tropic level; gross productivity; net productivity; Describe what an agricultural ecosystem is: Describe what is meant by productivity and give the formula: Explain how natural and agricultural ecosystems differ: Unit 4: Chapter 5: Energy and ecosystems 5.5 Chemical and biological control of agricultural pests: Key words: What are pests and pesticides? What are the features of an effective pesticide? How are biological agents used to control pests? What is integrated pest management? pests; pesticides; biodegrade; costeffective; accumulation; monoculture; conservation; Describe what pests and pesticides are: Explain what biological control is: Explain what an integrated pest control system is: State the features of an effective pesticide Explain how controlling pests effectively increases productivity: Unit 4: Chapter 5: Energy and ecosystems 5.6 Intensive rearing of domestic livestock: Key words: How does rearing animals intensively increase the efficiency of energy conservation? selective breeding; habitats; populations; antibiotic resistance; species diversity Explain how rearing animals intensively increases the efficiency of energy conservation: Unit 4: Chapter 5: Energy and ecosystems Exam questions Scientists constructed a mathematical model. They used this model to estimate the transfer of energy through consumers in a natural grassland ecosystem. The table shows their results. The R : A ratio is higher in mammalian primary consumers than in insect primary consumers. Suggest a reason for this higher value. (1 mark) The scientists tested their model by comparing the values it predicted with actual measured values. The graph shows their results. Complete the equation to show how net production is calculated from the energy in ingested food. P= (1 mark) Describe and explain how intensive rearing of domestic livestock would affect the figure for A in the first row of the table Evaluate the evidence in the graph. (1 mark) the figure for R in the first row of the table. (1 mark) Calculate the ratio of R : A for mammalian primary consumers. (1 mark) (3 marks) Unit 4: Chapter 5: Energy and ecosystems Exam questions Residual food intake (RFI) is the difference between the amount of food an animal actually eats and its expected food intake based on its size and growth rate. Scientists have selectively bred cattle for low RFI. Explain the advantage to farmers of having cattle with a low RFI. Bacteria in the digestive systems of cattle break down food and produce methane. Scientists investigated the relationship between RFI and methane production. They measured the rate of methane production of 76 cattle over a fifteen-day period. Some of the results are shown in Figure 3. (2 marks) When RFI is calculated, low values are negative. Explain why they are negative. Suggest a null hypothesis for this investigation. (1 mark) Scientists have developed a standard procedure for comparing RFI in cattle. They control two factors. These are type of food and environmental temperature. Explain why each of these factors needs to be controlled. Type of food (1 mark) Selectively breeding cattle with a low RFI may help to limit global warming. Use the information in Figure 3 to explain how. Environmental temperature (4 marks) (2 marks) Unit 4: Chapter 5: Energy and ecosystems Exam questions The diagram shows organisms in a food web. A pyramid of energy for this food web is shown below. The bars are drawn to the same scale. Use the pyramid of energy to calculate the percentage efficiency of energy transfer between producers and primary consumers. Show your working. Name all the secondary consumers in this food web. (1 mark) Use the diagram to explain the likely effect of a sudden decrease in the stickleback population on the population of mayfly larvae. efficiency = .......................................... % (2 marks) The average efficiency of energy transfer between producers and primary consumers in pyramids of energy is around 10 %. Suggest why the efficiency of energy transfer from producers to primary consumers in this food web is higher than 10 %. (2 marks) Energy from the sun may ultimately end up in dead plant matter. Describe how. (2 marks) (2 marks) Unit 4: Chapter 6: Nutrient cycles 6.1 The carbon cycle: Key words: Where does carbon enter the living component of the ecosystem? Where does carbon enter the non-living component of an ecosystem? What role is played by saprobiotic organisms in the carbon cycle? ecosystem; producers; consumers;; saprobiotic microorganisms; biomass; green house gas; photosynthesis; respiration; combustion; death; decay; feeding Explain the basis of all nutrient cycles using the diagram to help: Describe where carbon enters the living and nonliving components of the ecosystem: Fill in the carbon cycle: Describe the role played by saprobiotic organisms in the carbon cycle: Unit 4: Chapter 6: Nutrient cycles 6.2 The greenhouse effect and global warming: Key words: What is the greenhouse effect? Which are the major greenhouse gases and where do they come from? Why is the production of greenhouse gases increasing? How do greenhouse gases contribute to global warming? What are the consequences of global warming? greenhouse effect; greenhouse gases; global warming; niches; xerophytes; pathogens; Describe what the greenhouse effect is: State the main greenhouse gasses and describe where they come from: Describe what global warming is: Explain the consequences of global warming: Unit 4: Chapter 6: Nutrient cycles 6.3 The nitrogen cycle: Key words: How is nitrogen recycled in ecosystems? What is the role of saprobiotic microorganisms in this recycling? What do you understand by the terms ‘ammonification’, ‘nitrogen fixation’ and denitrification’? Where does nitrogen enter the living component of an ecosystem? Where does nitrogen enter the non-living component of an ecosystem? ammonification; nitrification; nitrogen fixation; denitrification; saprobiotic microorganisms Complete the diagram of the nitrogen cycle: Describe the following steps of the nitrogen cycle: Ammonification Nitrification: Nitrogen fixation Denitrification: Show where nitrogen enters the living and non-living component of the ecosystem. Unit 4: Chapter 6: Nutrient cycles 6.4 Use of natural and artificial fertilisers: Key words: Why are fertilisers needed in agricultural ecosystems? How do natural and artificial fertilisers differ? How do fertilisers increase productivity? natural/organic fertilisers; artificial/inorganic fertilisers; Explain why fertilisers are needed in agricultural ecosystems: Explain how fertilisers increase productivity Explain how natural and artificial fertilisers differ: Unit 4: Chapter 6: Nutrient cycles 6.5 Environmental consequences of using nitrogen fertilisers: Key words: What are the main environmental effects of using nitrogen fertilisers? What is meant by ‘leaching’ and ‘eutrophication’? How do these processes affect the environment? species diversity; leaching; eutrophication Describe the main environmental effects of using nitrogen fertilisers: Explain what leaching means and the effects it can have on the environment Explain what eutrophication means and the effects it can have on the environment: Unit 4: Chapter 6: Nutrient cycles Exam questions The diagram shows the nitrogen cycle. 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. (2 marks) Applying very high concentrations of fertiliser to the soil can reduce plant growth. Use your knowledge of water potential to explain why. Name process P. (1 mark) Name process Q. (1 mark) (2 marks) Unit 4: Chapter 6: Nutrient cycles Exam questions Much of Indonesia is covered with forest. Large areas of forest have been cleared and planted with oil-palm trees to be used in the production of fuel. In these forests, nitrogen in dead leaves is made available to growing plants by the action of bacteria. Describe the role of bacteria in making the nitrogen in dead leaves available to growing plants. (5 marks) Clearing the forests and burning the vegetation affects the carbon dioxide concentration in the atmosphere. Describe how and explain why. (4 marks) Unit 4: Chapter 6: Nutrient cycles Exam questions Insect pests of crop plants can be controlled by chemical pesticides or biological agents. Give two advantages of using biological agents. 1 The ecologists concluded that in this investigation control of the two-spotted mite by a biological agent was effective. Explain how the results support this conclusion. 2 (2 marks) Two-spotted mites are pests of strawberry plants. Ecologists investigated the use of predatory mites to control two-spotted mites. They released predatory mites on strawberry plants infested with two-spotted mites. They then recorded the percentage of strawberry leaves occupied by two-spotted mites and by predatory mites over a 16-week period. The results are shown on the graph. (2 marks) Farmers who grow strawberry plants and read about this investigation might decide not to use these predatory mites. Suggest two reasons why. 1 2 (2 marks) The ecologists repeated the investigation but sprayed chemical pesticide on the strawberry plants after 10 weeks. After 16 weeks no predatory mites were found but the population of two-spotted mites had risen significantly. Suggest an explanation for the rise in the two-spotted mite population. Describe how the percentage of leaves occupied by predatory mites changed during the period of this investigation. (2 marks) (2 marks) Unit 4: Chapter 7: Ecological succession 7.1 Succession: Key words: What changes occur in the variety of species that occupy an area over time? What are meant by the terms succession and climax community? How can managing succession help to conserve habitats? abiotic; biotic; ecosystems; communities; succession habitat; climax communities; biodiversity; biomass Explain what is meant by the terms: succession: Explain what changes occur in the variety of species that occupy an area over time: climax community: Unit 4: Chapter 7: Ecological succession 7.2 Conservation of habitats: Key words: What is conversation? How can managing succession help to conserve habitats? ecosystem; biodiversity; ethical; economic; cultural; aesthetic Explain what conservation is: Explain how managing succession can help to conserve habitats: Unit 4: Chapter 7: Ecological succession Exam questions Ecologists investigated succession in some abandoned crop fields. The data that they collected are shown in the graph. The curves show the trends that occurred over a period of 60 years. Explain the change in soil nitrate concentration shown on the graph. The pioneer plants had different characteristics from the plants that colonised the fields after 50 years. The pioneer plants had seeds that germinate better when the temperature fluctuates. Explain the advantage of this to these pioneer plants. (2 marks) Explain the advantage to a plant that colonises after 50 years of having a high rate of photosynthesis at low light intensities. (1 mark) Conservation of grassland habitats involves management of succession. Use the data in the graph to explain why. (2 marks) (2 marks) Unit 4: Chapter 7: Ecological succession Exam questions Succession occurs in natural ecosystems. Describe and explain how succession occurs. Describe how you would investigate the distribution of marram grass from one side of the dune to the other. (3 marks) Marram grass is a pioneer species that grows on sand dunes. It has long roots and a vertically growing stem that grows up through the sand. Sand dunes are easily damaged by visitors and are blown by the wind. Planting marram grass is useful in helping sand dune ecosystems to recover from damage. Use your knowledge of succession to explain how. (5 marks) (2 marks) Unit 4: Chapter 7: Ecological succession Exam questions The diagram shows the dominant plants in communities formed during a succession from bare soil to pine forest. The species that are present change during succession. Explain why. Name the pioneer species shown in the diagram. (2 marks) The pine trees in the forest have leaves all year. Explain how this results in a low species diversity of plants in the forest. (1 mark) (1 mark) Unit 4: Chapter 8: Inheritance and selection 8.1 Studying inheritance: What are meant by the terms ‘genotype’ and ‘phenotype’? What are dominant, recessive and co-dominant alleles? What are multiple alleles? Key words: Unit 4: Chapter 8: Inheritance and selection 8.2 Monohybrid inheritance: How are genetic crosses represented? How is a single gene inherited? Key words: Unit 4: Chapter 8: Inheritance and selection 8.3 Sex inheritance and sex linkage: How is sex determined genetically? What is sex linkage? How are sex linked diseases such as haemophilia inherited? Key words: Unit 4: Chapter 8: Inheritance and selection 8.4 Co-dominance and multiple alleles: How does co-dominance affect the inheritance of characteristics? How do multiple alleles affect inheritance? How are blood groups in humans inherited? Key words: Unit 4: Chapter 8: Inheritance and selection 8.5 Allelic frequencies and populations: What are meant by the terms ‘gene pool’ and ‘allelic frequency’? What is the Hardy-Weinberg principle? How can the Hardy-Weinberg principle be used to calculate allele, genotype and phenotype frequencies? Key words: Unit 4: Chapter 8: Inheritance and selection 8.6 Selection: How does reproductive success affect allele frequency within a gene pool? What is selection? What environmental factors exert selection pressure? What are stabilising selection and directional selection? Key words: Unit 4: Chapter 8: Inheritance and selection 8.7 Speciation: What is speciation? What is geographical isolation? How can geographical isolation lead to the formation of new species? Key words: Unit 4: Chapter 8: Inheritance and selection Exam questions More exam questions January 2010 Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter June 2011 Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter June 2010 Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter January 2012 Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter January 2011 Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter June 2012 Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter January 2013 Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter