|
Exam
techniques
Adrian
Whyte and Joanna Johnson, Contributor
 |
| Wolmers
Boys' School versus Donald Quarrie
in Manning Cup football action
at Harbour View Mini Stadium recently.
- Ian Allen Photo |
WHY
IS it that some capable students often
fail to obtain the quality grades that
are expected of them even when they
have worked hard and have a good grasp
of the content? This is usually due
to poor exam techniques.
Continuing
from last lesson, we will be looking
at a possible exam question and a
typical student's answer.
EXAM
QUESTION AND STUDENT'S ANSWER
1.
An experiment was carried out to investigate
the activity of a protease on gelatin
(a protein). Six test tubes were set
up containing the protease solution
and the gelatin each at a different
buffered pH. They were placed in a
water bath for 30ºC for five
minutes. The time taken for reaction
to occur was recorded. The results
are shown in the graph.
a)
What is the optimum pH of this enzyme?
The optimum pH of this enzyme is pH
10. 0/1
b)
How do you account for the changes
observed in the graph?
The
enzyme works best at a specific pH
and because of that, the reaction
was slower at certain pHs. 1/3
c)
Explain why the test tubes were placed
in the water bath for five minutes
before the results were recorded.
This
was done so the only limiting factor
would be the pH, as enzymes work best
at a specific temperature. 1/1
d)
Explain why little activity was found:
i)
when the experiment was repeated at
85ºC;
Enzymes
were denatured they work best
at a particular temperature.
1/2
ii)
When the protease was replaced with
distilled water.
Water
is not an enzyme. 0/1
e)
State one factor, other than pH, that
affects the way enzymes work.
Temperature.
1/1
f)
Explain the effect of the factor you
identified in e) above on enzyme action.
In
correct temperatures, the enzyme will
work at its best, but if it is too
high or too low, the reaction may
slow down or it may denature the enzyme.
3/3
Total:
8/12
HOW
TO SCORE FULL MARKS?
Part
(a) seeks to determine your understanding
of an enzyme controlled reaction,
and your ability to analyse graphs.
HINT:
Pay keen attention to the axis
labels. Many students tend to make
the mistake and assume that the highest
on the graph is automatically the
optimum pH. Notice that the label
on the 'y' axis is time taken for
reaction to occur and not rate of
reaction! Therefore, the enzyme working
at its best would take the least amount
of time to react, so the correct answer
will be pH 7.5.
Questions
like part (b) are usually not answered
well, because students tend to misinterpret
the question.
When
a question asks for an 'account',
you are expected to explain why something
is happening and not simply state
what is happening. A good answer should
state:
*
Enzyme works best at an optimum pH.
*
Outside of it optimum pH, the enzyme
is unable to function properly because
of changes to its structure. This
accounts for the increase time taken
for reaction to occur at pH 5 and
10.
HINT:
It is always good to refer to any
diagrams given in a question in your
answer.
Questions
such as part (c) & (d) are quite
common in the analysis paper. They
seek to pull on your knowledge from
your SBAs.
Part
(c) was a good answer. However, more
was required of the student in part
(d). Saying that the enzyme was denatured
in (d) i) was good, but the student
should have gone on to say that denaturing
destroys the structure of the enzyme,
therefore, it is unable to carry out
its function. In (d) ii), stating
that water was not an enzyme is not
good enough for a mark. Since this
answer will imply that if it was any
enzyme, the reaction will still go
on.
A
good answer would have been that distilled
water does not contain the enzyme
to break down the protein gelatin.
Parts
(e) & (f) are questions that test
your understanding of the topic area.
The
answers given by the student were
excellent. As they identified an appropriate
factor (temperature) and showed how
this factor affects the activity of
an enzyme.
* Adrian Whyte and Joanna Johnson
teach Biology at Ardenne High School.
|
