Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
Answers to end-of-chapter questions
c
Light Percentage
intensity / cover of M.
percentage perennis
of full sun
Rank
Light
intensity
Percentage
cover
D D 2
90 10 6 2.5 3.5 12.25
50 65 3 6 –3 9
axes labelled – concentration of calcium
carbonate / arbitrary units and numbers of
stoneflies;
points plotted accurately;[2]
b there is no relationship between water
hardness and numbers of stonefly nymphs.
[1]
c
30 90 2 8 –6 36
20 80 1 7 –6 36
80 34 4 5 –1 1
Number
of
stonefly
nymphs
Concentration
of calcium
carbonate /
arbitrary units
Rank
Stonefly Calcium
nymphs carbonate
D D 2
88 20 5 4 1 1
93 10 7 2.5 4.5 20.25
100 0 8 1 7 49
2 145 1 11.5 –10.5 110.25
3 80 2 9 –7 49
5 145 3 11.5 –8.5 72.25
n = 8 ΣD 2 = 164.5
r s = 1 – [
6 × ΣD 2
n 3 – n ]
r s = 1 – [
6 × 164.5
512 – 8 ]
r s = 1 – 1.958
r s = –0.95833
ranks stated correctly;
ΣD 2 calculated correctly;
correct numbers substituted into the
equation;
value of r s = –0.958 (or –0.96);[4]
d correlation coefficient is –0.958;
there is a negative correlation between light
intensity and percentage cover of M. perennis;
the critical value for 8 samples is 0.758, the
value of r s is greater than the critical value so
the null hypothesis is rejected;[3]
[Total: 10]
8 a
Number of stonefly nymphs
45
40
35
30
25
20
15
10
5
0
0 20 40 60 80 100 120 140 160
Concentration of calcium carbonate / arbitrary units
7 28 5 4 1 1
7 90 5 10 –5 25
7 75 5 8 –3 9
8 55 7 6.5 0.5 0.25
10 55 8 6.5 1.5 2.25
12 42 9 5 4 16
30 22 10 3 7 49
40 20 11 2 9 81
42 17 12 1 11 121
n = 12 ΣD 2 = 536
r s = 1 – [
6 × ΣD 2
n 3 – n ]
r s = 1 – [
6 × 536
1728 – 12]
r s = 1 – 1.874
r s = –0.874
ranks stated correctly;
ΣD 2 calculated correctly;
correct numbers substituted into the
equation
value of r s = –0.874 (or –0.87);[4]
d correlation coefficient is –0.874;
there is a negative correlation between water
hardness and numbers of stonefly nymphs;
the critical value for 12 samples is 0.544, the
value of r s is greater than the critical value so
the null hypothesis is rejected;
Cambridge International AS and A Level Biology © Cambridge University Press 2014