Biology 9700/52 — May/June 2016

Cambridge A-Level · Planning, Analysis and Evaluation · worked solutions for every part, with the mark scheme

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Topics Analysis, Conclusions and Evaluation · Planning

Q1Analysis, Conclusions and EvaluationPlanningFree sample

Grassland is an important breeding habitat for some birds. These birds feed on plant material and invertebrates. Biodiversity of the habitat is maintained by domestic herbivores, such as sheep, cows and goats, grazing on growing plant material.

A group of students investigated the effect of grazing by domestic herbivores on the plant biodiversity of a grassland as measured by Simpson’s Index of Diversity. They investigated two areas. One area was grazed by herbivores and the other area was not grazed for many years because it was surrounded by a fence to keep out the herbivores.

(a)

State the data that the students would have collected from the grazed and ungrazed areas to calculate Simpson’s Index of Diversity.

(b)

Describe a random (unbiased) method which the students could have used to collect the data needed to calculate the biodiversity of the plant species in the two areas.

The description of your method should be detailed enough for another person to follow.

(c)

The students also investigated the effect grazing had on the height of one particular species of plant. Their hypothesis was:

The mean height of the plant is greater in the ungrazed grassland than the grazed grassland.

State the independent and the dependent variables in this investigation.

independent variable = ______
dependent variable = ______

(d)

Table 1.1 shows the results of their investigation.

Table 1.1

sample number	height of plant / mm
	grazed area	ungrazed area
1	586	858
2	549	873
3	526	864
4	589	901
5	545	847
6	538	862
7	573	864
8	549	879
9	604	864
10	611	888
mean	567	870
mode	549
median	561

(i)

Complete Table 1.1 by writing the values of the mode and median for the ungrazed area.

(ii)

Use the information and formula below to calculate the standard error for these results.

Give your answers to 3 significant figures.

S_M = \frac{s}{\sqrt{n}}

$S_M$ = standard error
$s$ = standard deviation
$n$ = sample size (number of observations)

grazed area: $s = 29.5$
ungrazed area: $s = 15.7$

standard error, grazed area = ______
standard error, ungrazed area = ______

(iii)

Standard error is used to calculate 95% Confidence Intervals (CI).

The values for the grazed area are $548.3\ \text{mm}$ to $585.7\ \text{mm}$ .

Use the formula below to calculate the confidence intervals for the ungrazed area.

95\%\ \text{CI} = \text{mean} \pm 2\ S_M

Show your working.

ungrazed area ______ $\text{mm}$ to ______ $\text{mm}$

(iv)

State what information is gained by calculating the confidence intervals.

(e)

The students used the mark-release-recapture method to estimate the population of an invertebrate animal found living on the grassland. They used the formula:

\frac{\text{number of animals marked in the first sample} \times \text{total number of animals in the second sample}}{\text{number of marked animals in the second sample}}

State two precautions the students should have taken to ensure that the results they obtained were valid.

(f)

The population of an invertebrate that feeds on seeds was estimated in both the grazed and ungrazed areas. Predict which area would have the greatest population and give a reason for your choice.

choice = ______
reason = ______

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