Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
Answers to self-assessment questions
6 a
Species
Smaller species underneath a canopy of
larger ones are often ignored.
Large leafy plants are often overestimated
compared with other methods.
It can be time–consuming unless there is only
a small number of species to be sampled.
With an abundance scale, such as Braun–
Blanquet, some categories cover a wide
range of percentage cover so the results do
not discriminate, e.g. between 55 and 75%
cover – both are given the same score of 4.
Shore B
n n
N
( n N) 2
painted topshells 51 0.059 0.004
limpets 125 0.145 0.021
dogwhelks 63 0.073 0.005
snakelocks
anemones
0 0.000 0.000
beadlet anemones 22 0.026 0.001
barnacles 391 0.454 0.206
mussels 116 0.135 0.018
periwinkles 93 0.108 0.012
total number of
individuals, N
861 Σ( n N) 2 = 0.267
For shore B, Simpson’s Index of Diversity (D)
= 1 − 0.267 = 0.733
b Shore A has an index of 0.8 and shore B
has an index of 0.7. This means that shore
A has a greater biodiversity than shore B.
The absence of snakelocks anemones and
the small number of beadlet anemones on
shore B is not compensated for by the larger
numbers of barnacles. There are many more
limpets, dogwhelks, mussels and periwinkles
on shore A which contribute to the high value
for the index.
7 a
Species
Woodland
n n
N
( n N) 2
A 56 0.448 0.201
B 48 0.384 0.148
C 12 0.096 0.010
D 6 0.048 0.002
E 3 0.024 0.001
total number of
individuals, N
8 a
125 Σ( n N) 2 = 0.362
Simpson’s Index of Diversity (D) = 1 – 0.362
= 0.638
b An ecosystem that has one dominant
species that is very abundant may have a
large number of species but there would
be very few individuals of other species. If
abundance is measured, then there may be
many individuals of this dominant species,
but there may not be many other species so
it is species poor. An area with one dominant
species which is very abundant has a lower
biodiversity than an area with no dominant
species and many species of all roughly the
same abundance.
c The area of grassland has a high biodiversity,
the area beneath the conifer trees has a
much lower biodiversity.
Percentage cover of Vaccinium myrtillus
35
30
25
20
15
10
5
0
0
5 10 15 20 25 30 35 40
Percentage cover of Calluna vulgaris
b The data is ranked, with the lowest
percentage cover being ranked as 1, the next
is ranked as 2 and so on. If there are two
figures with equal percentage cover then
they are given an equal rank. In the example
Cambridge International AS and A Level Biology © Cambridge University Press 2014