Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
Answers to end-of-chapter questions
8 a i e.g. the rate of water loss from a
mesophyte will be greater than the rate of
water loss from a xerophyte;[1]
ii independent variable: collect, shoots /
leaves, from a mesophyte and xerophyte;
measuring the dependent variable: record
rate of movement of meniscus along
the capillary tube, include reference to
distance and time;
control variables: shoots / leaves, with
similar surface areas; same temperature /
wind speed / humidity;
procedure: cut shoot under water with
slanting cut;
dry shoot before beginning measurements;
ensure apparatus entirely airtight;
use syringe to begin with water at a
suitable point in the tubing;
leave for some time to settle down before
beginning to take measurements;
reliability: do repeats and calculate means;
risk: no significant risk / reference to care
needed when, cutting shoot / pushing
shoot into capillary; [max. 8]
iii suitable method described for finding the
volume of a cylinder;
refer to using distance moved by water in
this calculation;
or
use the syringe to push the water back to
its starting position;
measure volume of water needed to
do this; [max. 2]
b axes with independent variable on the x-axis
and the dependent variable on the y-axis;
suitable curve or bars to show results
(this depends on what is being measured
and how);[2]
c i area = 36/10 000 = 0.0036 m 2 ;
water loss = 0.018/30 = 0.0006 cm 3 min –1 ;
rate = 0.0006/0.0036 = 0.167 cm 3 m –2 min –1 ;
[3]
ii t-test;
comparing the means of two sets of, data
with normal distribution / continuous
data;[2]
d mesophyte has a greater transpiration rate
than the xerophyte;
both lose less mass when lower surface is
covered;
more water lost from lower surface than from
upper surface;
xerophyte loses almost no water from its
upper surface; [max. 3]
[Total: 21]
Cambridge International AS and A Level Biology © Cambridge University Press 2014