Energy & Ecosystems (A Level only) (AQA A Level Biology)

Exam Questions

2 hours15 questions
1a2 marks

Primary producers, such as plants, convert light energy from sunlight into chemical energy during photosynthesis.  

Give two ways in which plants use the molecules produced during photosynthesis.

1b1 mark

Define the term biomass.

1c2 marks

Biomass is usually measured using dry biomass

State why dry biomass is a more accurate measurement than wet biomass. 

1d2 marks

Describe how an organism's dry biomass would be calculated.

Did this page help you?

2a2 marks

Figure 1 below shows a simple example of a piece of equipment called a calorimeter.

Figure 1

8S1nvf4K_1

Describe how the calorimeter shown in Figure 1 could be used to estimate the stored chemical energy inside the dried plant sample shown.

2b2 marks

The simple calorimeter shown in Figure 1 does not produce a completely accurate estimate of the energy stored inside the plant tissue sample. 

Suggest two reasons why the estimate may not be completely accurate.

2c2 marks

An area of grass measuring 50 m2 was mown to obtain the grass cuttings used for the  plant sample burned in Figure 1. The total mass of the grass cuttings taken was 45 kg.

Use the information provided to calculate the gross primary production of the area of grass mowed in g m-2.

2d1 mark

Define the term gross primary production

Did this page help you?

3a1 mark

Figure 1 below shows the transfer of energy through a simple food chain.

Figure 1

VDphh9f0_2

Name the process indicated in Figure 1 by which solar energy is converted into GPP.

3b1 mark

The process of converting solar energy into GPP is not 100% efficient.

Suggest one reason why this might be the case.

3c2 marks

The position marked R in Figure 1 represents energy stored in the plant that is not converted into biomass in the consumer. 

Explain why this energy is not converted into biomass.

3d2 marks

Use information provided in Figure 1 to calculate the net primary productivity (NPP) of the producers in the food chain shown. 

Did this page help you?

4a2 marks

Figure 1 below shows the energy transfers taking place in a simple food chain. The energy values are all given in kJ m-3 yr-1

Figure 1

48E0ZuJG_3


Use the equation provided below to calculate the respiratory loss (R) of the algae in Figure 1.

NPP = GPP - R

4b2 marks

The net productivity in consumers can be calculated using the following equation:

N = I - (F + R)

N represents the net productivity of the consumer, while I represents the energy ingested by the consumer. 

State what is represented by F and R in this equation.

4c2 marks

Use information in Figure 1 and the equation provided in part b) to calculate the net productivity (N) of small fish in this food chain.

4d2 marks

The efficiency of energy transfer can be calculated using the following equation:

Efficiency of energy transfer (%) = fraction numerator N e t space p r o d u c t i v i t y space o f space t r o p h i c space l e v e l over denominator N e t space p r o d u c t i v i t y space o f space p r e v i o u s space t r o p h i c space l e v e l end fraction cross times 100 

Use information in Figure 1 and the equation provided to calculate the efficiency of energy transfer for zooplankton.

Did this page help you?

5a2 marks

Figure 1 below shows a series of feeding relationships that exist on farmland.

Figure 1

ZMe0FXVu_4

Identify two biotic factors shown in Figure 1 that would reduce the overall yield of the corn crop.

5b2 marks

State two ways in which the farmer in Figure 1 might reduce the impact of the factors identified in part a) to improve the overall yield of the corn crop.

5c2 marks

Two food chains are given below:           

Food chain A: Cornrightwards arrow Human
  Food chain B : Cornrightwards arrow Cow rightwards arrow Human

State which of food chains A or B would lead to the greatest energy transfer to humans. 

Explain your answer.

5d2 marks

It was suggested to the farmer that efficiency could be improved by keeping the cows inside a shed rather than letting them roam in the fields. 

Explain how keeping the cows inside a shed might improve the efficiency of cattle farming.

Did this page help you?

1a2 marks

The diagram in Figure 1 shows the transfer of energy through a sheep. The figures are in kJ × 106 year–1.

Figure 1

beQH0nir_1

i)
Suggest what label F in Figure 1 represents

ii)
Calculate the value of F in Figure 1.

1b1 mark

Calculate the value of P in Figure 1. Give your answer in kJ × 106 year–1.

1c2 marks

A farmer estimated that an area of 3,600 m2 of his farmland is required to sustain one sheep. The productivity of the grass on his farmland is 19,248 kJ m–2 year–1. Calculate the percentage of the energy in the grass that is used in the production of new tissue in one sheep (such as the sheep in Figure 1). Show your working.

1d2 marks

The farmer in part c) wanted to increase the net production of his livestock (his sheep) by keeping them indoors and in pens. Explain one way this could lead to a higher efficiency of energy transfer.

Did this page help you?

2a2 marks

Woodlice are detritivorous insects (they feed on the dead remains of plants). A biologist estimated the numbers of woodlice at two different sites in a woodland ecosystem. They also estimated the net primary production of the sites to see if this influenced the numbers of woodlice present. Their results are shown in Table 1 below.

Table 1

Site Number of woodlice per m2 Net primary production / g m–2 y–1
X 240 1320
Y 80 460

Although net primary production is a measure of plant biomass formed per year, it does not represent the total amount of plant biomass formed per year by photosynthesis. Explain why.

2b2 marks

Using the information in Table 1, explain why there is a greater number of woodlice in site X than in site Y. 

2c4 marks

One way to estimate plant yield is to measure the dry mass of the plant sample. Suggest how the biologist in part a) could determine the dry mass of plant material samples from sites X/Y and explain why the biologist shouldn’t use the fresh mass of these plant material samples to compare the plant yields of these two sites.

2d1 mark

The grass in an ecosystem has a gross primary production of 20,000 kJ m-2 yr-1. The net primary production of this grass is calculated to be 12,000 kJ m-2 yr-1. How much energy does one square metre of this grass lose as heat from respiration in one year?

Did this page help you?

3a1 mark

Figure 1 shows the net production of different trophic levels in a food chain.

Figure 1

hj0eAVPb_2

          

State the equation for the net production of consumers.

3b2 marks

The deer in Figure 1 ingests 17,874 kJ m-2 yr-1 of food. Calculate the total energy loss of the deer.

3c4 marks

In Figure 1, the net production of the deer is less than the net primary production of the grass. Explain why.

3d2 marks

The food chain in Figure 1 has three trophic levels. Explain why it is rare to find natural food web with more than five trophic levels.

Did this page help you?

4a2 marks

The total dry biomass of a 1 m2 patch of gorse plants growing in an area of moorland in Devon was measured each year for 20 years. The graph in Figure 1 shows the results of this study.

Figure 1

S3ATNnA6_3

Using the construction lines on the graph in Figure 1, calculate the mean yearly increase in biomass of the gorse plants in g yr-1.

4b4 marks

The graph in Figure 1 suggests that the gorse did not increase in biomass by the same amount each year. Giving examples, suggest what factors might cause this.

4c2 marks

A group of students estimated that the total light energy falling on the 1 m2 patch of gorse in Figure 1 was 2,563,000 kJ yr-1. Using a calorimeter, they also found the chemical potential energy in 1 g of the gorse to be 14.8 kJ. 

Use this information to calculate the efficiency of photosynthesis in the gorse plants in this 1 m2 patch.

4d3 marks

Suggest why the efficiency of photosynthesis in the gorse plants is relatively low.

Did this page help you?

5a2 marks

The graph in Figure 1 shows the percentage of wheat crop lost to two insect pests months before and 6 months after a chemical pesticide was sprayed on the crop.

Figure 1

vJYMf-Vs_4

How might the Rootworm beetle and the Weevil reduce the net primary production of the wheat crop in Figure 1?

5b2 marks

What can you conclude about the effectiveness of the chemical pesticide sprayed on the wheat crop in Figure 1?

5c2 marks

Suggest how the owner of the wheat crop in Figure 1 could further reduce the percentage losses caused to their crop by insect pests.

5d4 marks

The owner of the wheat crop in Figure 1 decides to use biological control against the insect pest. They introduce a species of toad. By eating the insect pests, the toads ingest 10,000 kJ m-2yr-1 of energy but lose 2,000 kJ m-2yr-1 of this energy in faeces and urine. They lose a further 7,000 kJ m-2yr-1 using energy for respiration.

Using the information above, calculate the net production of the toads and the percentage efficiency of energy transfer from the insects to the toads. Include the correct units in your answers.

Did this page help you?

1a2 marks

Define the term “trophic level” as used in ecology. 

1b6 marks

Figure 1 shows the energy flow through a woodland ecosystem. 

All units are in kJ m-2 year-1

Figure 1

GuXeGO3w_figure-1

Use Figure 1 to compare the percentage efficiency of the producers to that of the primary consumers. Explain the reasons why these energy transfers are not more efficient.   

1c4 marks

In Figure 1, suggest, with reasons, names for Processes Y and Z and describe their role in a food web.

1d6 marks

Livestock farmers can use the following methods to increase meat yields: 

  • Heated indoor sheds to rear livestock
  • Use of artificial feed, bought commercially  

Evaluate the use of these methods to allow farmers to manipulate energy transfers to their advantage when growing food for the meat industry.   

Did this page help you?

2a4 marks

Only around 1% of the light energy that reaches the Earth’s atmosphere is captured by plants and made available to other organisms in the food chain. Suggest reasons for this low value.  

2b2 marks

Fields on two separate farms, X and Y, were used to grow the same crop. The fields were divided into sections, with different masses of fertiliser containing nitrate ions added to these sections.  After two months, samples of the crop plants from each section were taken from the fields and their mass determined. The results are shown in Table 1.

Table 1

Mass of fertiliser added / kg ha-1

Mass of crop / kg m-2
Field X - used for grazing cattle in the previous year Field Y - used for the same crop in the previous year
0 11.0 5.8
10 16.5 9.5
20 17.7 12.3
30 17.6 15.8
40 17.6 17.0
50 17.6 17.1
60 17.5 17.1

        

Use Table 1 to explain the differences in the amounts of crop harvested from both fields at nitrate levels of 0 to 40 kg ha-1.

2c4 marks

Recommend a suitable application mass per hectare of fertiliser to the farmer responsible for Field X. Give reasons for your recommendation.  

2d6 marks

Outline an experimental method by which scientists can estimate the total amount of biomass in a crop field such as X or Y.

Did this page help you?

3a3 marks

Artificial fertilisers are used on farms to improve yields of crops such as barley. Fertilisers replace mineral ions removed from the soil when crops are harvested. Nitrate is one of these ions.

Give three nitrogen-containing molecules that a crop synthesises using nitrate ions. 

3b3 marks

Scientists investigated the use of artificial fertiliser on barley crops in a European country between 1960 and 1995. They calculated a Fertiliser Response Ratio (FRR) which is the number of kg of barley produced per kg of fertiliser used.  Figure 1 shows their results. (A hectare is a unit of area commonly used in agriculture)

Figure 1

cAaQYC~A_figure-2

Use Figure 1 to calculate the percentage change in the mass of barley produced per hectare in 1960 compared with 1995.

3c4 marks

Use the data in Figure 1 to evaluate the use of artificial fertilisers on barley crops.

3d2 marks

Barley is the fourth most common crop plant in the world. Its common uses are in animal fodder and for making malt, a major raw material in beer and whisky production. Much of its chemical energy (stored in its biomass) is not passed into these processes. 

Suggest two reasons why. 

Did this page help you?

4a3 marks

Figure 1 shows a bomb calorimeter, used for measuring the energy content of biomass. A sample of dry biomass is burned in pure oxygen, and the temperature change of the surrounding water is measured.  

Figure 1

ADrH1ERj_figure-3

Suggest why pure oxygen is used, rather than air. 

4b2 marks

A typical oak tree has a mass of 15,000 kg and can be assumed to be 50% dry mass.

Explain why the energy content of its biomass, measured in a calorimeter, can only be an estimate.

4c1 mark

Table 1 shows a mathematical model used to estimate the transfer of energy through consumers in a natural grassland ecosystem.  

Table 1

  Energy transferred as % of energy in the biomass of producers

Ingested food (IF)

Absorbed in         digestion (AD)

  Egested
    (EG)

Net Production

(NP)

Respiratory Loss

(RL)

Primary consumers          
Mammals 25.00 12.50 12.50 0.25 12.25
Insects 4.00 1.60 2.40 0.64 0.96
Secondary consumers          
Mammals 0.16 0.13 0.03 0.003 0.127
Insects 0.17 0.135 0.035 0.040 0.095

Write an equation to show how Net Production (NP) is calculated from the energy in ingested food. 

NP = 

4d3 marks

Using the data in Table 1, calculate the ratio RL:AD for mammal primary consumers and for insect primary consumers and explain the difference between the two calculated values.  

Did this page help you?

5a2 marks

Farmers and scientists have selectively bred sheep to have a low Residual Food Intake (RFI). This is calculated as the difference between the amount of food an animal actually eats and its expected food intake based on its size and growth rate.

Explain the advantage to farmers of having sheep with a low RFI.

5b2 marks

Bacteria found in the digestive systems of sheep break down food and produce Methane. Scientists investigated the relationship between RFI and methane production. They measured the rate of methane production of 140 sheep over a ten-day period. Some of their results are shown in Table 1.

Table 1

 

Low RFI

High RFI

Mean rate of methane production 

/ g day–1

21.3

30.5

Use the data to identify and explain two benefits that will arise from the use of low RFI feeds. 

5c5 marks

Other scientists investigated the release of methane from rice fields. This second group of scientists investigated the effect of adding organic material (straw) and mineral substances on the release of methane from rice fields. 

The results are shown in Table 2.

Table 2

Mineral substance
added to the soil

Total methane released over 15 days / μmol kg-1 soil

Without straw With straw
None 559 12 578
Nitrate 32 379
Sulfate 9 73
Iron oxide 21 154
Manganese oxide 25 248

Evaluate the claim that rice farmers should treat their fields with sulfate and refrain from using straw.  

5d2 marks

Methane is produced by microorganisms in the soil. The scientists found that rice fields that are flooded produce larger volumes of methane than rice dry fields.

Suggest why.

Did this page help you?