unit 4: populations and the environment chapters: 1 – populations 2 – atp 3 – photosynthesis 4...

Unit 4: Populations and the environment

Chapters:1 – Populations2 – ATP3 – Photosynthesis4 – Respiration5 – Energy and ecosystems6 – Nutrients cycles7 – Ecological succession8 – Inheritance and selection

Exam dates:

Friday 13th June 2014 – pm

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: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?

Key words: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 ecosystem:

Explain what is meant by the term populations:

Explain what is meant by the term community:

Explain what is meant by the term habitat:

Explain what is meant by the term ecological niche:


1.2 Investigating populations: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?

Key words:habitat, abundance, quadrat, sample, random, transect, frequency, percentage cover, mark-release-recapture, analysis

Explain the factors that should be considered when using a quadrat:

Explain what is meant by the term random sampling, and how you would ensure that a sample is truly random:

Explain how you wold sample along a transect:

Explain how you would measure abundance:

Explain what mark-release-recapture is and how it is used to estimate population size:

Explain how you would analyse the data:


1.3 Variation in population size: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?

Key words:population, population growth curve, limiting factors, abiotic, biotic, pH, temperature, light, water, humidity

Explain how the following factors affect population size:pH:

light:

temperature:

water and humidity:

Explain what factors affect the size of a given population:

Label and explain the stages of the population growth curve:


1.4 Competition:What is intraspecific competition?What factors do different species compete for?What is interspecific competition?How does interspecific competition influence population size?

Key words:competition, intraspecific, intraspecific, population, niche,

Explain what intraspecific competition is:

Explain how interspecific competition influences population size:

Explain what interspecific completion is, in your answer include information on the factors different species complete for:

Explain what is happening in this graph:


1.5 Predation:What is predation?How does the predator-prey relationship affect the population size of the predator and the prey?

Key words:predator, prey, predation, population, ecosystem, selection pressure

Explain what is happening in this graph:Explain what predation is:

Explain the effect predator-prey relationships have on population size:


1.6 Human populations:How does the human population growth curve differ from that of most other organisms?What factors affect the growth and size of human populations?

Key words:migration, emigration, immigration, birth rate, death rate, survival, life expectancy

Use the graphs to helpyou explain:Stable population:

Increasing population:

Decreasing population:

Explain how the following factors that affect human population, and how they are calculated:Migration:

Birth rate:

Death rate:


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)


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 showinga population that stays the same size

(1 mark)a population that is increasing in size.

(1 mark)

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.

Answer .....................................................(2 marks)


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.

(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)

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.

(3 marks)


Exam questions

The scientists calculated a correlation coefficient for these data.State a null hypothesis that would be appropriate for this investigation.

(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.

Describe the relationship between the number of feather mites present on each great tit and the size of the oil gland.

(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: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?

Key words:

State what energy is:

State why organisms need energy:

Describe how ATP stores 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)

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

3.1 Overview of photosynthesis:How is the plant leaf adapted to carry out photosynthesis?What are the main stages of photosynthesis?

Key words: ATP, photosynthesis, cuticle, light-dependent reaction, protons, electrons, NADP, grana, thylakoids, lamellae, stroma, chloroplasts


3.2 The light-dependent reaction: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?

Key words:ATP, photolysis, oxidation, reduction, electrons, chlorophyll, thylakoids,

Describe oxidation and reduction:

Describe how chloroplasts are adapted to carry out the light-dependent reaction:

Explain how ATP is made:

Explain photolysis:


3.3 The light-independent reaction: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?

Key words:ATP, NADP, Calvin cycle, stomata, stroma,

Explain the steps of the Calvin cycle:

Explain the link between the Calvincycle and the light-dependentreaction:

Describe where the light-independent reaction takes place:

Describe the lollipop experiment:


3.4 Factors affecting photosynthesis: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?

Key words:light-intensity, carbon dioxide, temperature, limiting factor, photosynthesis

Explain how light intensity can affect the rate ofphotosynthesis:

Explain how carbon dioxide concentration canaffect the rate of photosynthesis:

Explain how temperature can affect the rate ofphotosynthesis:

Explain the law of limiting factors:


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.

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)

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.

(3 marks)


Exam questions

During photosynthesis, carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (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.

(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.

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 light-independent reaction.

(3 marks)

Unit 4: Chapter 4: Respiration

4.1 Glycolysis:Where does glycolysis fit into the overall process of respiration?What are the main stages of glycolysis?What are the products of glycolysis?

Key words: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:


4.2 Link reactions and the Krebs cycle: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?

Key words:oxidised; eukaryotic cells; glycolysis; substrate-level phosphorylation;

Explain the link reaction: Name the coenzymes and state why they are important:

Explain what happens in the Krebs cycle:

Explain the significance of the Krebs cycle:


4.3 Electron transport chain: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?

Key words: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:


4.4 Anaerobic respiration: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?

Key words:glycolysis; Krebs cycle;

Explain how energy is released by anaerobic respiration:

Describe the production of ethanol by plants and microorganisms:

Describe the production of lactate in animals:

Compare the energy yields from aerobic and anaerobic respiration:


Exam questions

The biochemical pathway of aerobic respiration involves an number of different steps. Name one step in which carbon dioxide is produced

(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.

(2 marks)

When the apple slices were transferred to nitrogen, the following biochemical pathway took place:

Use this pathway to explain the part played by reduced NAD when the apple slices were transferred to nitrogen

(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)


Exam questions

A student measured the rate of aerobic respiration of a woodlouse using the apparatus shown in the diagram.

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)

What measurements should the student have taken to calculate the rate of aerobic respiration in mm3 of oxygen g–1 h–1?

(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)


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.

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)

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.

(3 marks)

Unit 4: Chapter 5: Energy and ecosystems

5.1 Food chains and food webs: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?

Key words:producers; consumers; decomposers; trophic level; food chain; food web; habitat; detritivores

Explain the following terms:Trophic level:

Food chain:

Food web:

Producer:

Consumer:

Decomposer:

Describe how energy enters an ecosystem:

Describe how energy is transferred between organisms in an ecosystem:

Describe how energy is lost from the ecosystem:

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:


5.2 Energy transfer between trophic levels: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?

Key words:ecosystem; net production; energy transfer; percentage efficiency;

The efficiency of energy transfers is calculated using the following equation:

Calculate the energy efficiency for this example:Energy available after the transfer = 50kJm-2year-1

Energy available before the transfer = 250kJm-2year-1


5.3 Ecological pyramids:What are the different types of ecological pyramid?What are the relative merits and disadvantages of each?

Key words:pyramid of numbers; pyramid of energy; pyramid of biomass

Explain what a pyramid of numbers is:

Explain the advantages of using a pyramid of numbers:

Explain the disadvantages of using a pyramid of numbers:

Explain what a pyramid of biomass is:

Explain the advantages of using a pyramid of biomass:

Explain the disadvantages of using a pyramid of biomass:

Explain what a pyramid of energy is:

Explain the advantages of using a pyramid of energy:

Explain the disadvantages of using a pyramid of energy:


5.4 Agricultural ecosystems:What is an agricultural ecosystem?How do natural and agricultural ecosystems differ?What is meant by productivity?How is productivity calculated?

Key words: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:


5.5 Chemical and biological control of agricultural pests: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?

Key words:pests; pesticides; biodegrade; cost-effective; accumulation; monoculture; conservation;

Describe what pests and pesticides are:

State the features of an effective pesticide

Explain what biological control is:

Explain what an integrated pest control system is:

Explain how controlling pests effectively increases productivity:


5.6 Intensive rearing of domestic livestock:How does rearing animals intensively increase the efficiency of energy conservation?

Key words:selective breeding; habitats; populations; antibiotic resistance; species diversity

Explain how rearing animals intensively increases the efficiency of energy conservation:


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.

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 affectthe figure for A in the first row of the table

(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)

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.

Evaluate the evidence in the graph.

(3 marks)


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.

(2 marks)When RFI is calculated, low values are negative. Explain why they are negative.

(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

Environmental temperature

(4 marks)

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.

Suggest a null hypothesis for this investigation.

(1 mark)Selectively breeding cattle with a low RFI may help to limit global warming. Use the information in Figure 3 to explain how.

(2 marks)


Exam questions

The diagram shows organisms in a food web.

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.

(2 marks)

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.

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)

Unit 4: Chapter 6: Nutrient cycles

6.1 The carbon cycle: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?

Key words: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: Fill in the carbon cycle:

Describe where carbon enters the living and non-living components of the ecosystem:

Describe the role played by saprobiotic organisms in the carbon cycle:


6.2 The greenhouse effect and global warming: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?

Key words: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:


6.3 The nitrogen cycle: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?

Key words:ammonification; nitrification; nitrogen fixation; denitrification; saprobiotic microorganisms

Complete the diagram of the nitrogen cycle:

Show where nitrogen enters the living and non-living component of the ecosystem.

Describe the following steps of the nitrogen cycle:Ammonification

Nitrification:

Nitrogen fixation

Denitrification:


6.4 Use of natural and artificial fertilisers:Why are fertilisers needed in agricultural ecosystems?How do natural and artificial fertilisers differ?How do fertilisers increase productivity?

Key words:natural/organic fertilisers; artificial/inorganic fertilisers;

Explain why fertilisers are needed in agricultural ecosystems:

Explain how natural and artificial fertilisers differ:

Explain how fertilisers increase productivity


6.5 Environmental consequences of using nitrogen fertilisers:What are the main environmental effects of using nitrogen fertilisers?What is meant by ‘leaching’ and ‘eutrophication’?How do these processes affect the environment?

Key words: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:


Exam questions

The diagram shows the nitrogen cycle.

Name process P.

(1 mark)Name process Q.

(1 mark)

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.

(2 marks)


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)


Exam questions

Insect pests of crop plants can be controlled by chemical pesticides or biological agents.Give two advantages of using biological agents.1

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.

Describe how the percentage of leaves occupied by predatory mites changed during the period of this investigation.

(2 marks)

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 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.

(2 marks)

Unit 4: Chapter 7: Ecological succession

7.1 Succession: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?

Key words:abiotic; biotic; ecosystems; communities; succession habitat; climax communities; biodiversity; biomass

Explain what changes occur in the variety of species that occupy an area over time:

Explain what is meant by the terms:succession:

climax community:


7.2 Conservation of habitats:What is conversation?How can managing succession help to conserve habitats?

Key words:ecosystem; biodiversity; ethical; economic; cultural; aesthetic

Explain what conservation is: Explain how managing succession can help to conserve habitats:


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.

(2 marks)

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)


Exam questions

Succession occurs in natural ecosystems. Describe and explain how succession occurs.

(5 marks)

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.

(2 marks)


Exam questions

The diagram shows the dominant plants in communities formed during a succession from bare soil to pine forest.

Name the pioneer species shown in the diagram.

(1 mark)

The species that are present change during succession. Explain why.

(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)

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:


8.2 Monohybrid inheritance:How are genetic crosses represented?How is a single gene inherited?

Key words:


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:


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:


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:


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:


8.7 Speciation:What is speciation?What is geographical isolation?How can geographical isolation lead to the formation of new species?

Key words:


Exam questions

More exam questions

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June 2010Question 1 – Chapter Question 2 – Chapter Question 3 – Chapter Question 4 – Chapter Question 5 – Chapter Question 6 – Chapter Question 7 – Chapter Question 8 – Chapter






unit 4: populations and the environment chapters: 1 – populations 2 – atp 3 – photosynthesis 4...

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terms population

given population

abiotic factors

population growth curve

term habitat

term populations

intraspecific competition

following factors