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1.
Describe how standard deviation is useful in comparing ecological data between two sites.
(Total 4 marks)
2.
(a)
Simpson’s index is given by the following equation:
D
N N  1
nn  1

where:
D = the diversity index, N = the total number of all species found and n = the number of
individuals of a particular species.
(i)
State what would happen to this index if the numbers of one species increased but
the total number of species stays the same.
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(1)
(ii)
State what a high value of D suggests about an ecosystem.
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(1)
(b)
Explain the use of biotic indices in monitoring environmental changes.
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(3)
(Total 5 marks)
1
3.
(a)
Temperature is an abiotic factor affecting distribution of plant species. State one other
abiotic factor that affects the distribution of plant species.
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(1)
(b)
To test how temperature affects growth, some plants were grown at 20°C and another
group at 30C. After a number of weeks, the heights of the plants were measured. Explain
how the t-test could be used to test the significance of the effect of temperature on plant
growth.
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(3)
(Total 4 marks)
4.
(a)
Define the term random sample.
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(1)
2
(b)
Draw and label a graph showing the sigmoid (S-shaped) population growth curve.
(3)
(c)
The masses of two different populations of sparrows (Passer domesticus) are shown in
the table below.
(i)
Population 1:
mass of birds / g
Population 2:
mass of birds / g
24.5
26.9
25.0
23.2
24.0
23.6
25.0
31.0
24.5
27.9
24.8
28.3
Calculate the mean value of the mass of birds for population 1.
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(1)
3
(ii)
With reference to the data shown, explain what is meant by the term standard
deviation. No calculation is expected.
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(2)
(Total 7 marks)
5.
(a)
A researcher measured the mean size of leaves from two trees of the same species in
different habitats. State one statistical test used to see if there is a significant difference in
the leaf size.
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(1)
(b)
Outline two important tasks in managing nature reserves.
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(2)
4
(c)
Explain the principle of competitive exclusion.
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(3)
(Total 6 marks)
6.
When estimating the size of a plant population in an area a random sample is often used. What
is a random sample?
A.
A sampling method that covers every part of the area being investigated.
B.
A sampling method that ensures that each part of the area being sampled has an equal
chance of being measured.
C.
A sampling method that systematically visits evenly spaced sites in the area being
investigated.
D.
A sampling method that only visits the parts of the area where the species is growing.
(Total 1 mark)
7.
For the following 10 measurements 4, 5, 5, 6, 6, 6, 6, 7, 7, 8 the mean value is 6. What is the
best estimate of the standard deviation?
A.
8
B.
6
C.
3
D.
1
(Total 1 mark)
5
8.
10 000 melons were collected from plants in the same area. Assuming their sizes are normally
distributed, how many melons would you expect to be within two standard deviations of the
mean?
A.
3400
B.
5000
C.
6800
D.
9500
(Total 1 mark)
9.
The average leaf length of one plant is 2.5 cm with a standard deviation of 0.5 cm. What does
this indicate?
A.
95% of all leaves fall within the ranges of 2.0 to 3.0 cm
B.
68% of all leaves fall within the ranges of 1.5 to 3.5 cm
C.
68% of all leaves fall within the ranges of 2.5 to 3.0 cm
D.
95% of all leaves fall within the ranges of 1.5 to 3.5 cm
(Total 1 mark)
10.
Which equation should be used to calculate the mean of a set of values?
(highest value – lowest value)
2
A.
lowest value +
B.
(highest value – lowest value)
 68%
2
C.
total of all values
number of values
D.
number of values
× 100%
total of all values
(Total 1 mark)
6
11.
What do error bars on graphs show?
A.
If the data is correct or not.
B.
How variable the data is.
C.
Which result is closest to the true result.
D.
What statistical technique was used to eliminate incorrect results.
(Total 1 mark)
12.
standard deviation (sd) is a measure of the spread about the
mean value;
68% of values fall within 1 sd of the mean;
small sd means data is clustered around the mean;
the larger the sd the greater the spread of the data;
the larger the sd the less useful the mean is for comparing data;
quoting the formula for sd;
as the means and sd become closer, the less likely the data
from the two sites are different;
the sd can be used to help decide whether the difference
between the two means is likely to be significant;
[4]
13.
(a)
(b)
(i)
D decreases;
(ii)
stable ecosystem / absence of changes;
ecosystem not under stress;
ancient / well established ecosystem;
biotic indices use a range of species;
of varying degrees of tolerance;
to measure an abiotic factor;
example of factor (eg organic water pollution, air pollution);
example of index (eg fresh water benthic invertebrates, lichens);
biotic indices can reveal long-term effects of environmental stress;
1
1 max
3 max
[5]
14.
(a)
(b)
light;
water;
soil pH;
salinity;
soil drainage;
mineral nutrients;
1 max
to see if there is (significant) difference between means of two populations;
7
a null hypothesis is stated / alternative hypothesis says data are different;
mean heights found;
a table is used according to degrees of freedom;
if value is greater than critical value, there is (significant) difference / reject
the null hypothesis;
so temperature does make a difference;
if value is not greater temperature has no effect;
3 max
[4]
15.
(a)
a sample where every member of a population has an equal
chance of being selected / sample selected without bias
1
(b)
axes correctly labeled (x = time, y = number of individuals / population size);
carrying capacity / plateau correctly labelled;
transitional / lag phase correctly labelled;
exponential growth phase / stage correctly labelled;
3 max
(c)
(i)
(ii)
24.6 g / 24.63 g (units needed)
Award [0] for 25 g or significant figure errors.
standard deviation is a measure of variability /
degree of spread around the mean;
a small standard deviation indicates the data is spread
closely around the mean value /
a large standard deviation indicates a wider spread around the mean;
population 2 has greater variability, therefore, it has a greater
standard deviation / vice versa;
. 1 standard deviation from the mean represents
68% of the data /
. 2 standard deviations from the mean represent
95% of the data;
1
2 max
[7]
16.
(a)
t-test / student test / student t-test
(b)
control of alien species;
restoration of degraded areas;
control of human exploitation;
promotion of the recovery of threatened species;
1
2 max
8
(c)
a species in an ecosystem occupies a niche;
the niche is all the roles of the organism in the community;
no two species can occupy the same niche in the community;
there is competition for same resources;
one will increase in number and the other decrease / die out;
3 max
[6]
17.
B
[1]
18.
D
[1]
19.
D
[1]
20.
D
[1]
21.
C
[1]
22.
B
[1]
9