Cambridge International A Level Biology Revision Guide

Cambridge International AS Level Biology
Answers to self-assessment questions
Answers to SAQs
Chapter 3
1 a
Amount of starch in mixture
Time
b Calculate the slope of the curve right at the
beginning of the reaction.
2 In case of inaccuracy of measurement at
30 seconds. The shape of the curve is more
likely to give an accurate value.
3
Initial rate of reaction
Enzyme concentration
If substrate
becomes
limiting, the
addition of
extra enzyme
cannot increase
the rate of
reaction.
4 Measure the volume of oxygen given off over
regular time intervals for several hydrogen
peroxide–catalase reactions at different
temperatures. In each case, all conditions
other than temperature must remain
constant. In particular, the volume and
concentration of hydrogen peroxide solution,
and the volume and concentration of
catalase solution must be kept constant each
time. Plot volume of oxygen against time for
each reaction. Calculate the slope of the line
at the beginning of the reaction in each case
to give the initial reaction rate. Then plot
initial reaction rate against temperature.
5 a Haemoglobin is the coloured pigment
that causes bloodstains. Protein-digesting
enzymes hydrolyse haemoglobin to amino
acids, which are colourless. They are also
soluble, so will wash away in water.
b Many protein-digesting enzymes have an
optimum temperature of around 40 °C.
c Other components of washing powders, such
as the oil-removing detergents, work best at
high temperatures.
6 One possible answer is as follows; other
answers might be equally acceptable.
Set up two sets of five tubes containing
equal volumes of the same concentration
of milk suspension. Make up five buffer
solutions of varying pH. Add equal volumes
of buffer solution, two of each pH, to the milk
suspension. To one set of tubes, add equal
volumes of trypsin solution. To the other set
of tubes, add the same volume of water; these
act as controls. Time the disappearance of
cloudiness in each tube. Plot rate of reaction
(1/time taken) against pH.
7 As soon as the reaction starts, the substrate
starts to be used up so the substrate
concentration starts to fall. This results in a
corresponding fall in the rate of reaction. It is
the initial rate at the start of the experiment
that is the true rate.
8 a
[S]
/arbitrary
units
1/[S]
/arbitrary
units
v
/arbitrary
units
1/v
/arbitrary
units
0.02 50.0 0.025 40.0
0.04 25.0 0.041 24.4
0.06 16.7 0.052 19.2
0.08 12.5 0.061 16.4
0.10 10.0 0.067 14.9
0.20 5.0 0.085 11.8
Cambridge International AS and A Level Biology © Cambridge University Press 2014