|
Looking
at past-paper questions
Monacia
Williams, Contributor
Hello
students, how are you all today? By
now many of you would have started
your external examinations and I sincerely
hope they have been going well for
you. Pretty soon you will be sitting
the biology exam and if you have been
paying attention to all that we have
been doing then you should do well.
For
the next two lessons we are going
to look at some questions from past
examination papers, seeing how best
they can be approached and answered.
OK, ready? Let's go then!
We
will begin by looking at Section A,
question one. This question is worth
25 marks and usually asks you to use
the skills you have gained from doing
laboratory work. These can be drawing
skills - equipment, organisms, graphs,
tables; you can be asked to draw anything
so be prepared.
Question
A
student wanted to test the following
hypothesis: 'Housefly larvae 'maggots'
respond negatively to light.' He used
the apparatus shown in Figure 1 for
his investigation.
(a)
In the space provided, produce a diagram
to show how the apparatus in Figure
1 could have been set up for this
investigation. 4 marks
Answer
Ensure
that you use the pieces of equipment
that are given; do not introduce other
pieces. Look carefully at Figure 1,
organise the equipment in your mind
then draw. Remember, your diagram
is incomplete without labels.
(b)
The student recorded his results in
Table 1.
TABLE
1. RESULTS OF CHOICE CHAMBER INVESTIGATION
|
Location
of the 20 larvae
|
|
Trial
|
Dark
Side
|
Light
Side
|
|
1
2
3
|
11
15
14
|
9
5
6
|
|
Total
|
|
|
|
Percentage
|
|
|
(i)
Complete the table by calculating
the total and percentage of larvae
on the dark side and the light side
of the petri dish. 2 marks
Answer
Total
- Dark side - 40, Light side - 20
Percentage
- Dark side - 66.7%, Light side -
33.3%
(ii)
Do the results support the students
hypothesis? Give a reason for your
answer.
2
marks
Answer
Do
you remember the hypothesis? It expected
the larvae's response to be negative
to light. So, the answer is yes. For
you to gain the full marks you must
include the reason.
Reason
In
the three trials, more larvae were
found on the dark side than on the
light side.
(iii)
Name TWO factors OTHER THAN light
that could have influenced the larvae's
response.
2
marks
Note
The
capital letters are important clues
and must be followed to allow you
to gain full marks.
This
calls on your knowledge of irritability
in animals to provide the answer.
Answer
Moisture
and temperature
(iv)
Describe how the apparatus shown in
(a) could be modified to investigate
ONE of the factors named in (b) (iii).
2 marks
In
order to test the response to moisture,
you would need to provide and withhold
moisture. Moisture can be provided
using the damp cotton wool and withheld
using something that can absorb water
vapour. This can be done by using
anhydrous calcium chloride.
Answer
Factor
- Moisture
The
damp cotton wool can be placed in
one side of the petri dish and anhydrous
calcium carbonate can be placed in
the other side below the wire gauze.
Both sides can then be covered with
the black paper to exclude light.
(v)
Explain how the response shown by
the larvae in this experiment could
help them to survive in their natural
environment. 2 marks
What
is the larvae's natural environment?
The eggs are laid in food remains,
either plant or animal. These are
usually in some stage of decomposition
so the conditions would be moist and
dark.
Answer
Keeping
away from light and staying in moist
areas would prevent the larvae from
becoming dried out, due to the thinness
of their skins.
Next
week we will complete the question.
See you then!
Monacia
Williams teaches at Glenmuir High
School. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
|
