Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
Answers to end-of-chapter questions
or
record number of species and calculate
species density;
or
record percentage cover (for those species it
is difficult to count);[3]
[Total: 9]
5 a 44 and 36;[1]
b one plant may overlie another, so both would
be included in the cover for the quadrat. [1]
c it is difficult to estimate the percentage cover
with any more precision than this. [1]
d these results cannot be used to estimate
species frequency;
there may have been plants present that did
not cover 5% of a quadrat;
there could be cowslips in all the quadrats
but only in number 4 were there enough to
cover an area that could be rounded up to
5% (e.g. 2.6% is the smallest area that can be
rounded up to 5%);
they would give an underestimate of species
frequency for small plants;
five quadrats is a small sample;
results are, unreliable / not representative, of
the whole area;[4]
e Any four of the following
climate;
soil type / soil depth / soil fertility;
temperature, qualified; e.g. by minimum /
maximum / mean annual / AW
drainage / rainfall / irrigation / water supply;
grazing / predation (by primary consumers /
herbivores);
availability of light / shading;
parasites / pests;
presence or absence of symbionts in the
ecosystem (e.g. fungi and bacteria that live in
mutualism with many plants);
application of, herbicides / fertilisers / other
named agricultural chemical;
type / frequency, of cultivation; [max. 4]
[Total: 11]
7 a
the marking must not influence the animal’s
behaviour;
the marking must not put animals at greater
risk of predation;
animals must mix at random after release;
there is no, immigration into the waste
ground / emigration from the waste ground;
no ‘birth’ of beetles or death between the
two sampling times; [max. 3]
c One way to do this is by random sampling with
quadrats
generate random numbers to give
coordinates for positioning quadrats;
put 10 (or more) quadrats on the field;
leave for several hours; (because putting
down the quadrats may have disturbed the
animals)
on return move the rice plants gently to
disturb the planthoppers and count them;
calculate the mean number per quadrat;
calculate an estimate of the number of
planthoppers in the field by dividing the area
of the field by the area of the quadrat and
multiplying the answer by the mean number
of planthoppers per quadrat; [max. 4]
[Total: 9]
Percentage cover of Mercurialis perennis
100
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100
Light intensity / percentage of full sun
axes labelled – percentage cover and light
intensity / percentage of maximum;
points plotted accurately;[2]
b null hypothesis – there is no relationship
between the light intensity and the
percentage cover of M. perennis. [1]
6 a 39 × 35
20 × 100;
68;[2]
b the marking must, not harm the animal / be
non-toxic;
Cambridge International AS and A Level Biology © Cambridge University Press 2014