in this bundle there are more than 5000 aqa a level biology questions and if you do every question and memorise the mark scheme you will get that A* without a doubt
50. The charts show some results from a survey of water quality and species diversity at nine sites
along a stream on the Isle of Wight in 1988. Sewage was discharged into the stream at certain
points.
K ey
In d iv id u a ls p e r k ic k s a m p le
M o re th a n 1 0 0 1 0 to 9 9 1 to 9
M a y fly
la rv a e
H o g lic e
S h rim p s
0 1 2 3 4 5 6 7 8 9
D is ta n c e d o w n th e s tre a m
4 0
3 5
3 0
C o n c e n tra tio n o f
2 5
a m m o n iu m io n s /
m g d m –3 2 0
1 5
1 0
5
0
0 1 2 3 4 5 6 7 8 9
D is ta n c e d o w n th e s tre a m
S ite s w h e re s e w a g e w a s d is c h a rg e d
(a) The animals were collected by kick sampling. In this technique, a net is held in the water.
Animals disturbed by kicking the streambed are collected inside the net.
Describe one precaution that should be taken to ensure that valid comparisons could be
made between samples taken from different sites.
(b) List the species in order of their tolerance to pollution by sewage.
Most tolerant ...................................................................
Medium tolerance ...................................................................
Sir George Monoux Sixth Form College 1
, Least tolerant ...................................................................
(1)
S (c) Explain why the concentration of ammonium ions was high in the samples of water taken
from the sites where sewage was discharged into the stream.
S (d) In 1989 all houses in the area were connected to drains and so sewage no longer entered
the stream. Following this, the oxygen concentration in the stream increased.
Explain why.
, 32
51. Plants growing in a field were supplied with a radioactive isotope of phosphorus, P.
The plants took up this isotope and incorporated it into substances in their tissues.
At intervals, four different species of animal living in the field were sampled and the amount of
radioactive phosphorus in their tissues was measured. The results are shown in the graph.
A n im a l s p e c ie s
A
B
C o n c e n tra tio n
o f 32P in tis s u e s
C
D
0 1 2 3 4 5 6
T im e / w e e k s
The four species of animal, A to D, were the consumers in a single food chain.
(a) To which trophic level does species C belong? Give a reason for your answer.
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