AQA A Level Biology

Energy Flow through Ecosystems assessment

Name: _____________________

Overall percentage and grade /32 Highlight the skills and knowledge
you need to work on

Short answers – knowledge recall and

application q1a + d, q2a,c,d, q3 ( /17)

Mathematical skills q1b + c, 2b, 4a ( /7)

Experimental data analysis 4b,c,d ( /8)

Smart targets:

What skills or knowledge do you need to work on?

What will you do and by when?

Knowledge and understanding qus

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Q1. (a) Put a Tick (✓) in the box next to the equation that shows how the net production of
consumers, N, can be calculated where
I represents the chemical energy store in ingested food
F represents the chemical energy lost to the environment in faeces and urine
R represents the respiratory losses to the environment.

N = (I – F) + R

N = I – (F + R)

N = I + (F + R)

N = I – (F – R)

(1)

In the UK, some female cattle are only used for breeding. This female breeding herd has
dairy cows and beef cows.

The table below shows data on dairy cows and beef cows in the UK female breeding herd
in December 2013 and December 2017.

Total number in Percentage of total female

Date female breeding breeding herd
herd / millions Dairy cows Beef cows

December 2013 3.35 54 46

December 2017 3.45 55 45

(b) In December 2017, the female breeding herd was 48% of all female cattle in the UK.
Use the table above to calculate the percentage of all female cattle that were beef
cows in the UK in December 2017.

Answer _______________ %
(1)

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(c) Use the table above to calculate the increase in the number of dairy cows in the UK
female breeding herd between December 2013 and December 2017.

Show your working.

Increase in number _______________

(2)

(d) Farming cattle for humans to eat is less efficient than farming crops because of
energy transfer.
Explain why.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________
(2)
(Total 6 marks)

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Q2. The diagram shows the energy flow through a freshwater ecosystem.
All units are kJ m–2year–1.

(a) Name

(i) process A;

______________________________________________________________
(1)

(ii) the group of organisms represented by box B.

______________________________________________________________
(1)

(b) Calculate the percentage efficiency with which light energy is transferred to energy
in producers. Show your working.

Answer ____________________
(2)

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 (c) Describe the effect of light energy in the light-dependent reaction of photosynthesis.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________
(2)

(d) If a plant is kept in the dark it is still able to produce carbohydrates, as long as it is
provided with two products of the light-dependent reaction of photosynthesis. Give
the name of these products and explain their function in the light-independent
reaction of photosynthesis.

Name _____________________________________________________________

Function ___________________________________________________________

___________________________________________________________________

Name _____________________________________________________________

Function ___________________________________________________________

___________________________________________________________________
(4)
(Total 10 marks)

Q3. The diagram shows the flow of energy through a marine ecosystem.

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 (a) Give one reason why not all the light energy falling on the producers is used in
photosynthesis.

___________________________________________________________________

___________________________________________________________________
(1)

(b) The producers in this ecosystem are seaweeds, which have a large surface area to
volume ratio. Give two advantages to seaweeds of having a large surface area to
volume ratio.

1. _________________________________________________________________

___________________________________________________________________

2. _________________________________________________________________

___________________________________________________________________
(2)

(c) Some species of seaweed are submerged in water for most of the time. Explain how
being under water might affect the rate of photosynthesis.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________
(3)
(Total 6 marks)

Data analysis and practical techniques

Q4. Ecologists developed a method for estimating the biomass of trees in a plantation.
The plantation consisted of trees of the same species.

They collected samples of wood from trees. For each sample they:

• determined the density of the freshly cut wood

• dried the wood in an oven at 103 °C for 24 hours
• determined the volume of the dried wood sample
• determined the density of the dried wood.

The table below shows data about one wood sample.

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 Volume of freshly Density of freshly Volume of dried Density of dried
cut wood sample cut wood wood sample wood sample
/ dm3 / g per dm3 / dm3 / g per dm3

1.345 993.0 1.125 769.0

(a) The loss of mass of the wood sample was due to loss of water. Water has a density
of 1 g per cm3.

Use the data in the table to calculate the percentage of water in the freshly cut wood
sample. Show your working.

Percentage of water = __________________________________

(2)

(b) The ecologists dried the samples in an oven at 103 °C for 24 hours. Describe how
the ecologists could have determined whether or not this drying removed all the
water from a sample of wood.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________
(2)

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(c) Ecologists then investigated the relationship between the diameter of the trunk of
the trees and their biomass.

The graph below shows their results. Each point is the result for one tree.

What does the graph show about the relationship between the diameter of the trunk
of the trees and their biomass?

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________
(2)

(d) Plantations of trees are often created to remove carbon dioxide from the
atmosphere, to help to balance the carbon dioxide released by burning fossil fuels.

For different species of tree, information is available for:

• the relationship between diameter of trunk and freshly cut biomass

• the percentage of water in fresh-cut wood
• the mean dried density of wood.

Using only the information provided in part (c), suggest how the mass of carbon in
the wood of a plantation of trees of a particular species could be estimated.

Start with measuring the diameter of a large number of trees.

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Assume that the dry biomass of a tree consists of biological molecules that contain
carbon.

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

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___________________________________________________________________

___________________________________________________________________
(4)
(Total 10 marks)

Page 9 of 12
Mark schemes

Q1.
(a) N = I – (F + R);
1

(b) 21.6
1

(c) Correct answer of 88500 = 2 marks;;

Incorrect answer but shows 1897500 = 1 mark

OR

Incorrect answer but shows 1809000

= 1 mark
Accept 88500 in any correct mathematical form.
Accept 1897500 and 1809000 in any correct mathematical
form.

(d) 1. More/three trophic/feeding levels (farming cattle);

Accept converse.

2. More energy lost via respiration (farming cattle);

Accept more energy lost via heat/excretion/faeces/ muscle
contraction (farming cattle)
2
[6]

Q2.
(a) (i) respiration;
1

(ii) decomposers;
(accept bacteria / fungi)
1

(b) × 100 = 5.14 / 5.1%;

(correct answer = 2 marks)
(principle: energy in producers ÷ energy of light absorbed =
1 mark)
2

(c) excites chlorophyll / electrons;

release electron(s);
2 max

(d) reduced NADP;

reduces GP / to change GP to TP;
ATP;
provides the energy to reduce GP / convert GP to TP / TP to RuBP /

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 provides phosphate to convert TP to RuBP;
4
[10]

Q3.
(a) transmission / reflected / misses chlorophyll / chloroplasts / wrong wavelength;
1

(b) (larger area) to absorb light;

(larger surface area) to absorb carbon dioxide;
short diffusion pathway for gases / oxygen / CO2;
light able to penetrate to all cells;
2 max

(c) effect;
detail;
effect on photosynthesis;
some effects are less light / light absorbed by water
different wavelength of light
temperature
availability of carbon dioxide
availability of water
(more than one effect award 1 mark only)
3
[6]

Q4.
(a) 1. 35.22 or 35.23% = 2 marks;

Award 1 mark if only fresh and dry masses correct, 1335.59 and 865.13 g;
2

(b) (After 24 hours)

1. Record mass and reheat;

Accept return to oven = reheat

2. Until constant mass recorded;

2

(c) 1. Positive correlation (between diameter and biomass);

2. Not linear / geometric / exponential / gradient gets steeper;

2

(d) 1. Calculate a mean diameter;

2. (Use this to) estimate / determine the mean fresh biomass of trees;

3. Use the percentage water content to find the dried biomass;

4. Use the dried density to calculate the mass of tree;

5. Count / estimate the number of trees in plantation and multiply by (mean)

carbon content (to find total carbon);
4 max

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 [10]

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