AQA A Level · Biology 7402
4 multiple-choice questions marked as you go, and 4 written questions with worked solutions. All on Populations in ecosystems.
In a specific habitat, the population of a sessile species of moss was estimated using random sampling with quadrats. 20 quadrats, each measuring \(0.5\text{ m} \times 0.5\text{ m}\), were placed across a field measuring \(100\text{ m} \times 100\text{ m}\). The mean number of moss patches per quadrat was found to be \(12\).
What is the estimated total population of moss patches in the field?
In an ecosystem undergoing primary succession on bare volcanic rock, which of the following is the most significant role of the pioneer species in allowing later seral stages to develop?
During primary succession on bare rock, which of the following best explains how pioneer species change the abiotic environment to allow for the growth of later-stage species?
A scientist is estimating the population of a mobile species of beetle in a woodland area using the mark-release-recapture method. On the first day, 120 beetles are captured and marked. On the second day, 80 beetles are captured, of which 15 are marked.
Calculate the population size. If the marks used were toxic and caused some beetles to die before the second capture, how would this affect the estimate?
A student used a 0.5 m \(\times\) 0.5 m quadrat to estimate the population of daisies in a rectangular field measuring 20 m by 50 m. In 10 randomly placed quadrats, the mean number of daisies per quadrat was 6.
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}Calculate the estimated total population of daisies in the field and state one assumption regarding the distribution of the plants required for this estimate to be valid.
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A scientist used the mark-release-recapture method to estimate the population of snails in a garden. She captured 40 snails, marked them, and released them. A week later, she captured 35 snails, of which 7 were marked.
Calculate the estimated population size of the snails using the formula:
\( N = \frac{n_1 \times n_2}{m_2} \)
Show your calculation.
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In an ecosystem undergoing primary succession, pioneer species often change the abiotic conditions of the environment.
Explain how these changes can lead to a decrease in the species richness of the pioneer community while increasing the overall stability of the climax community.
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Succession is a dynamic process that occurs in ecosystems.
(a) Explain how pioneer species facilitate the process of primary succession on bare rock and why they are eventually replaced by other species. (3 points)
(b) Contrast abiotic and biotic factors, providing one example of each that could limit the carrying capacity of a population in a climax community. (2 points)
(c) Describe how an ecologist could use randomly placed quadrats to estimate the population density of a non-motile species in a large meadow. (3 points)
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