Chapter 5
Answers
Marks
1 a) kJ m−2 yr −1
1
b) i)
ii)
0.64% (or 0.636%)
1
Heat / respiration:
muscle contraction;
faeces / indigestible material / food
not eaten;
excretion
2 max
2 a) stickleback and dragonfly nymphs
early summer pyramidal shape but
with 2nd level widest;
autumn – correct pyramidal shape;
shows 5 levels – labels producer,
primary consumer, secondary
consumer
2
b) ii)
mass unit per unit volume or mass
per unit area, for example
kg cm−3 or kg m−2
1
some energy lost at each stage in the food 2
chain / transfer of energy not 100%
efficient / lost in respiration;
only a limited amount of energy is
available / at each stage less is available for
next stage / little energy left at top of
food chain
3 a) 8–24 ºC
AQA Biology A2 level © Nelson Thornes Ltd 2009
All 3 units are needed. However,
answers which include joules, with any
area, and any time are acceptable.
Most energy is transferred to the
environment as heat energy from
respiration. A common error is to state
that respiration uses energy.
1
b) i)
c)
Examiner’s tips
1
Both shapes must be correct for the first
mark. Note – most food chains will
always produce a pyramid of biomass.
Energy transfer between trophic levels
is usually between 5–20% efficient.
Accept 7.5 to 8.4 and 23.5 to 24.4
This represents net productivity, that is,
gross productivity minus respiratory
loss.
1
Chapter 5
Answers
Marks
b) Photosynthesis rate only just above
respiration rate;
Little gain in biomass or net loss in
biomass due to night-time respiration;
No excess production for storage in tubers
c)
2
Optimum for enzymes exceeded / enzymes 2
denatured;
Light independent reaction disrupted
4 a) no competition / weaker competition in
2 max
US;
no organisms to eat it / no pathogens
to infect it in US;
environment / abiotic factors more
favourable / specific example, for example
temperature / water availability;
more reproduction
Examiner’s tips
Storage in tubers can only occur when
net productivity is high.
High temperatures are not always
required for the denaturation of
enzymes.
These are common factors in explaining
why an organism introduced into an
ecosystem becomes a pest.
b) Either yes because reduces;
stays low;
or
no because reduces;
but does not get rid of plants completely
2
You will often be asked to evaluate
data. It is important to use the data as
evidence to support your conclusions.
c)
i)
number of fire-ants falls rapidly /
most killed / within six months;
then population remains low
2
It is always advisable to quote figures
from the graph although here it was not
essential. For example, ‘the population
fell by over 95% in the first six months’.
c)
ii)
most fire-ants killed;
(some survive because) some
resistant;
insecticide does not affect all stages
of life cycle;
insecticide does not reach all
individuals, for example underneath
leaf;
survivors reproduce;
because of reduced competition /
greater availability of food
3 max
This could be explained in terms of
natural selection, that is some fire-ants
already possessed some resistance due
to a mutation. Alternatively, it could be
explained in terms of the application or
effectiveness of the insecticide.
AQA Biology A2 level © Nelson Thornes Ltd 2009
2
Chapter 5
Answers
Marks
d) specific (to one pest);
only needs one application / reproduces;
keeps population low;
the pests do not develop resistance;
does not leave chemical residues in
environment;
can be used in organic farming;
does not get rid of pest completely;
may become a pest itself;
slow acting / takes time to reduce pest
population
5 a) greenflies take in insecticide from roses /
leaves;
ladybirds eat large numbers of greenflies;
bioaccumulation idea / insecticide cannot
be excreted / remains in the body / stored
in fat / not broken down
6 max
Examiner’s tips
Learn these advantages and
disadvantages of using biological
control.
3
b) i)
chemical: numbers fluctuate
2
throughout year;
biological: numbers fairly constant
throughout year / accurate description
b) ii)
number of plants drops because of
spraying / reapplication, then rises
because insecticide washed away /
new plants grow
c)
i)
chemical: some plants / parts of plants 2
not sprayed / spray washes off before
it has effect;
plant may be resistant to spray
A common error by candidates is to use
the term ‘immune’ rather than resistant.
c)
ii)
biological: because the biological
control agent never eats all plants;
as weeds diminish so do control
agents / is balance between food and
consumer
A knowledge of predator-prey
relationships is required here.
AQA Biology A2 level © Nelson Thornes Ltd 2009
Do not simply repeat all the information
provided on plant numbers. You should
describe the general pattern shown by
the data.
1
2
3
Chapter 5
Answers
6 a) i)
a) ii)
Marks
Examiner’s tips
P = C − R − U − F;
or P = C − (R + U + F) or equivalent
1
3.74 kJ × 106 years−1
1
Units must be given as kJ × 106 years−1
2 max
1 mark given for the correct calculation
but incorrect answer.
b) Correct answer: 2.18
Or
Correct use of data but wrong answer:
a) ii) × 10 6 × 100
21135 × 8100
c)
Less energy lost as heat / in maintaining
body temperature / in movement
1
7 a) light is wrong colour / frequency /
wavelength / does not strike chlorophyll
molecule / chloroplasts / there is another
limiting factor
1
b) energy is lost in respiration;
(small amount is) lost as heat;
lost to decomposers / lost in excretion /
leaf fall/death and decay;
part of oak tree not eaten / not digested
c)
2 max
each bird has several / many parasitic
2 max
mites;
but total mass / energy of mites is less than
that of one bird
AQA Biology A2 level © Nelson Thornes Ltd 2009
4