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Question 1
A group of students investigated the size of a ladybird population within a woodland. Ladybirds exist as part of a community within the woodland. |
a) | What is meant by a community?
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b) | Describe how the students could use the mark-release-recapture method to estimate the size of the ladybird population.
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c) | Give two conditions that are necessary for the mark-release-recapture results to be valid.
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d) | The students collected 83 ladybirds in their first sample and later collected 98 ladybirds, 14 of which were marked. Use this information to calculate the number of ladybirds in the woodland.
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Question 2
A group of scientists investigated the ecosystem on a sand dune. Ecosystems consist of biotic and abiotic factors. |
a) | What is meant by an abiotic factor?
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b) | Describe how the scientists could determine the average percentage cover for marram grass on a sand dune.
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c) | The sand dune has undergone the process of succession and is now made up of a climax community. Give two features of a climax community.
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d) | Describe and explain how the process of succession occurs.
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Question 3
Some plant species grow on roadside verges and may be sprayed with salt from salt spray applied to the roads in the winter. A student wanted to investigate the distribution of plant species in these areas. |
a) | Describe how they could use a transect to investigate how plant species distribution changes with increased distance from the road.
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b) | Suggest one limitation of using a transect to collect this data.
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c) | The results from the student’s investigation are shown below.
Describe the data shown in the kite diagram above.
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d) | One of plant species X, Y, or Z also grows in coastal ecosystems. Predict which species grows in coastal areas. Explain your answer.
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Question 4
A conservation group wanted to estimate the population size of leopards in the Samburu national reserve in Kenya. They placed cameras around the reserve which were activated by movement. |
a) | Suggest why the group did not use the mark-release-recapture method to estimate the size of the leopard population.
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b) | The conservation group also used footprints to estimate the size of the population. Suggest two disadvantages of using footprints.
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c) | The group did use mark-release-recapture to estimate the population size of pangolins in the reserve. Explain how.
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d) | Suggest why the mark-release-recapture method may produce unreliable results in large nature reserves.
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Question 5
A group of ecologists studied the growth of algae on a rocky shore. They placed concrete blocks on a rocky shore and recorded the percentage cover of different species at regular intervals. Their results are shown in the table below.
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a) | The ecologists concluded that the process of succession had taken place on the concrete blocks. Explain what is meant by succession.
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b) | Use the information above to name the pioneer species.
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c) | Explain how the data in the table provide evidence of succession.
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d) | Explain why the ecologists measured percentage cover of the algae rather than frequency.
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Question 6
An ecologist studied the population sizes of a species of bird. In this species, young birds leave their nests from June to July and spend the months of August to February feeding in woods and gardens. From March to May a pair of adult birds form a separate territory that they use for breeding. |
a) | Explain why using the mark-release-recapture technique would yield unreliable results during July.
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b) | Explain why using the mark-release-recapture technique would yield unreliable results during April.
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c) | The ecologist carried out the mark-release-recapture method in September. She trapped 34 birds, marked them and released them. Later she collected a second sample in which 16 birds were marked and 23 were not. Use this information to estimate the size of the bird population.
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d) | Some scientists suggest using the base sequences of DNA to estimate the size of populations using mark-release-recapture. Explain how this would work.
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Question 7
Some plants grow in a clustered distribution, whereas others grow in a random distribution. The diagram below shows a clustered and a random distribution.
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a) | Describe how quadrats can be used to investigate whether a plant species has a clustered or random distribution.
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b) | Some plants found in deserts are found in a uniform distribution in which individual plants are widely spaced. Suggest and explain how this distribution provides an advantage to the plants.
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c) | A scientist investigated the populations of black garden ants, Lasius niger, and yellow meadow ants, Lasius flavus. He used the mark-release-recapture method and estimated the population sizes using two different calculations, the Lincoln estimate and the Chapman estimate. Calculate the population sizes of each ant species using the equations below:
Lincoln estimate: population=mn1×n2 Chapman estimate: population=((m+1)(n1+1)×(n2+1))−1 where n = number of individuals in a particular sample and m = number of marked individuals in the second sample.
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d) | Give one difference between the population estimates given by the two equations.
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Question 8
Crop yield can be determined by measuring the dry mass of plants. |
a) | Suggest how a student could find the dry mass of a plant material sample.
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b) | Suggest an advantage of using dry mass rather than fresh mass to compare crop yields.
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c) | In natural ecosystems, most light that falls on plants is not used in photosynthesis. Suggest two reasons why.
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d) | Farming animals for humans to eat is less efficient than farming crops for humans to eat. Use your knowledge of energy transfer to explain why.
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Question 9
The diagram below shows the flow of energy through an ecosystem. |
a) | Name the organisms represented by box X in the diagram above.
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b) | Name process Y in the diagram above.
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c) | Define the terms producer and trophic level.
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d) | Farmers can increase the efficiency of energy transfer from primary consumers to humans. Suggest three ways in which farmers can achieve this.
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Question 10
The diagram below shows the percentages of energy transferred from sunlight to a shrew in a woodland ecosystem.
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a) | Describe how the percentage efficiency of energy transfer between producers and primary consumers can be calculated.
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b) | Use the diagram above to calculate the percentage of sunlight energy that is used in respiration within a shrew. Give your answer to 3 significant figures.
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c) | In this woodland ecosystem the net productivity of the vegetation is 25,468 kJ m-2 year-1. Use the diagram above to calculate the energy stores in new biomass of the shrew in kJ m-2 year-1. Give your answer to 2 decimal places.
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d) | Farmers often keep their livestock indoors. Suggest and explain why.
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Question 11
The diagram below shows a simplified representation of the nitrogen cycle. |
a) | Which process, A, B, or C in the diagram above, involves denitrification?
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b) | Describe the role of microorganisms in the production of nitrates from the remains of dead organisms.
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c) | Some nitrogen-fixing bacteria are found in the leaves of crops. These bacteria only produce ammonia from nitrogen inside cells known as heterocysts. These cells have thick walls and do not contain chlorophyll. Heterocysts are located next to photosynthetic cells and produce anaerobic conditions inside their cells. Suggest how the features of heterocysts allow improved efficiency of nitrogen fixation.
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d) | Farmers often use crop rotation as a method for producing high crop yields. This method involves growing a different crop each year in the same field. Suggest two ways in which this method may lead to higher crop yields.
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Question 12
An animal within an ecosystem dies and decays. The diagram below shows what happens to some of the nitrogen-containing compounds within the animal’s body.
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a) | Name substances X and Y in the diagram above.
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b) | Name process Z in the diagram above.
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c) | Saprobionts are involved in the decay of animals. Describe how.
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d) | Nitrogen in the atmosphere can also form nitrogen-containing compounds that can be absorbed by plants. Describe how.
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Question 13
The table below shows some of the reactions involved in the cycling of nitrogen within ecosystems. |
a) | Complete the table by naming the type of bacteria that carries out each reaction.
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b) | Nitrogenase catalyses the reduction of nitrogen during nitrogen fixation. The reaction requires 16 ATP molecules to reduce each molecule of nitrogen. Nitrogenase also catalyses reactions involving other substances. What does this suggest about the shapes of these other substances?
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c) | When ammonia inhibits nitrogenase activity, nitrogen-fixing bacteria may benefit. Explain how.
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d) | Another cycle within ecosystems is the carbon cycle. Describe four similarities between the carbon cycle and the nitrogen cycle.
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Question 14
The diagram below shows the carbon cycle.
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a) | Name substance X in the diagram above.
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b) | Name processes A, B, and C in the diagram above.
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c) | The carbon in dead plants is returned to the atmosphere via the carbon cycle. Describe this part of the carbon cycle.
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d) | The concentration of carbon in the atmosphere varies throughout the year. Suggest why the concentration of carbon in the atmosphere increases during the winter months.
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Question 15
A group of scientists investigated the effect of temperature on cattle growth and the efficiency at which the cattle converted their food into new biomass. Their results are shown in the diagram below.
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a) | Suggest two variables the scientists should control in this investigation.
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b) | Describe the effect of temperature on average growth rate of cattle.
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c) | Use the data to suggest why the scientists did not investigate temperatures higher than 35°C.
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d) | The efficiency at which cattle convert their food into new biomass is lower at 0°C compared to 15°C. Suggest and explain why.
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