CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK
Sample answers have been written by the authors.
Coursebook answers
Chapter P1
Self-assessment questions
1
temperature each time by heating or by
adding hot water.
aThe independent variable is temperature.
The dependent variable is the activity of
amylase.
b The most important control variables will
be pH, concentration of amylase solution
and concentration of starch suspension.
bThe lower end of the range should begin
around 0 °C. It cannot be any lower than
this, as this is the freezing point of water.
The upper end of the range should be
about 80 °C – although it could go up to
just below 100 °C. This wide range would
ensure that the optimum temperature
of the enzyme is included (optimum
temperatures are not always around
40 °C and can be much higher or lower
than this).
cA suitable interval would be 10 °C. This
gives a good compromise between getting
plenty of readings (if the range is 0 °C
to 80 °C there will be nine readings) and
making it possible to do the investigation
in a reasonable amount of time.
2
3
1
You can measure the dependent variable by
measuring the rate of disappearance of starch
or by measuring the rate of appearance of
reducing sugar (maltose).
a Temperature (the independent variable)
could be changed using a water bath.
Partly fill a beaker with crushed ice.
Measure the temperature using a
thermometer. Stand a tube containing
amylase solution, and a separate tube
containing starch suspension, in the ice.
Leave for five minutes before adding them
to one another. For the next temperature,
either heat the ice gently or add hot
water until the water reaches the desired
temperature. Continue upwards through
the temperature range, increasing the
c pH can be controlled using a buffer
solution at a value that is close to the
optimum pH for amylase (a value between
pH7 and pH8 would be suitable). Add the
same volume of buffer to each reacting
mixture. Amylase concentration and
starch concentration can be controlled by
making up enough of each solution to use
for each temperature. Stir the solutions
thoroughly before taking out each sample.
4
The precise structure of the results table
will vary, depending on the range of the
independent variable that has been decided
on, the interval, and how the dependent
variable will be measured. The results
table should:
•
have ruled columns and rows
•
include the independent variable
(temperature) in the first column, headed
‘Temperature / °C’, and each value listed
from lowest to highest as a pure number
(no units except in the heading)
•
include a column for readings of the
dependent variable (second column)
headed appropriately with the unit.
I f repeats are to be done, the results table
could include three columns for readings of
the dependent variable, and a final column in
which the mean values for each temperature
can be recorded.
Cambridge International AS & A Level Biology © Cambridge University Press 2020
CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK
5
a
Answers will depend on the points chosen.
Answers should include:
•
a tangent drawn at each of the chosen
points
•
working showing the values of x and
y for each tangent
•
calculation of y ÷ x for each tangent
•
final answer expressed with units.
b The last paragraph should be modified to
include specific references to the gradients
calculated in a.
6
2
Reflection
Learners are likely to decide that they understand
the investigation better if they have been involved
in planning it themselves. Just following a list of
instructions often results in a tendency to simply
do what the instructions say, without any effort
to think about why the experiment is being done
in this way. Learners may be able to suggest how
they can deal with this, perhaps by spending some
time thinking about the reasons for each step on a
worksheet or in an examination question, before
actually beginning to do the practical work.
Enzyme concentration remains constant, so
the number of active sites available to break
down rennin is constant. Assuming that all the
active sites are always occupied (i.e. that the
enzyme is working at its maximum velocity,
Vmax), then each rennin molecule can only
enter an active site after its previous occupant
has been broken down and left (as product).
The more rennin molecules there are, the
longer it will take for all of them to undergo
this process.
Cambridge International AS & A Level Biology © Cambridge University Press 2020