5.3 Energy and ecosystems

Question 1

Are plants producers or consumers?

Answer 1

producers

Question 2

Why are plants producers?

Answer 2

because they can produce their own carbohydrates (glucose) via photosynthesis

Question 3

What is lost between each trophic level?

Answer 3

energy

Question 4

How is energy lost between each trophic level?

Answer 4

via respiration and excretion

Question 5

What is biomass?

Answer 5

The mass of carbon or dry mass of tissue per given area.

Question 6

How can you measure biomass?

Answer 6

by removing all the water

Question 7

What does the productivity of an ecosystem depend on?

Answer 7

the biotic + abiotic factors

Question 8

What will maximise the productivity of an ecosystem, and why is this good?

Answer 8

lots of water, light, warmth + green plants will maximise the rates of photosynthesis, therefore resulting in more carbohydrates being produced

Question 9

What is Gross Primary Production (GPP)?

Answer 9

The chemical energy store in plant biomass in a given area or volume

Question 10

What is Net Primary Production (NPP)?

Answer 10

The chemical energy store in plant biomass, taking into account the energy lost due to respiration (R)

Question 11

NPP = ?

Answer 11

GPP - R

Question 12

What is NPP in simple terms?

Answer 12

the energy left over that is available to the plant to create new biomass + therefore available to the next trophic level in a food web.

Question 13

What is the equation for the net production of consumers?

Answer 13

N = I - F + R

Question 14

In the equation N = I - F + R, what does N stand for?

Answer 14

net production of consumers

Question 15

In the equation N = I - F + R, what does I stand for?

Answer 15

the chemical energy store in ingested food

Question 16

In the equation N = I - F + R, what does F stand for?

Answer 16

the chemical energy lost to the environment in faeces + urine

Question 17

In the equation N = I - F + R, what does R stand for?

Answer 17

respiratory losses

Question 18

What is the units for the net production of consumers?

Answer 18

KJ ha-1 year-1

Question 19

Why is it recorded as per unit area?

Answer 19

to standardize the results to enable environments to be compared

Question 20

Why is it recorded as per year?

Answer 20

• to take into account the impact that seasons will have on rain, light + heat.
• it provides annual average to allow for comparisons between environments.

Question 21

Succession occurs in natural ecosystems. Describe and explain how succession occurs. (4)

Answer 21

• (Colonisation by) pioneer species;
• pioneer species change the environment (e.g. by forming soil)
• environment becomes less hostile for new species
• there is an increase in biodiversity
• to climax community

Question 22

Biofuels are fuels which can be produced from plants. Scientists have developed a standard method called net life-cycle carbon dioxide production (NLP) to find the overall effect of producing and using particular biofuels on carbon dioxide production.

(a) Petroleum is used as a comparison when evaluating NLPs of biofuels. Suggest two reasons why (2)

Answer 22

• Is widely / commonly used;
• Produces large amount of carbon dioxide;

Question 23

Producing and using biofuels from corn ethanol results in a negative percentage change in carbon dioxide production. Explain why. (2)

Answer 23

• CO2 taken up in photosynthesis;
• More taken up than produced (when it is used) with less CO2 produced than petrol;

Question 24

Large areas of land have to be used to grow the plants to make biofuels. Ecologists have suggested that changes in land use could lead to a decrease in biodiversity.
Suggest how changes in land use could lead to a decrease in biodiversity. (2)

Answer 24

• fewer species
• fewer habitats

Question 25

Residual food intake (RFI) is the difference between the amount of food an animal actually eats and its expected food intake based on its size and growth rate. Scientists have selectively bred cattle for low RFI. (a) (i) Explain the advantage to farmers of having cattle with a low RFI. (2)

Answer 25

- Reduced cost; - Less feed

Question 26

When RFI is calculated, low values are negative. Explain why they are negative. (1)

Answer 26

Amount of food taken in less than expected.

Question 27

Methane is produced by anaerobic microorganisms in the soil. The scientists found that rice fields that are not flooded do not produce large amounts of methane. Suggest why. (2)

Answer 27

- flooding produces anaerobic conditions - more active aerobic microorganisms

Question 28

In the previous year, field A had been used for grazing cattle. Field B had been used to grow the same crop as this year. When no fertiliser was added, the mass of crop from field A was higher than from field B. Explain this difference. (2)

Answer 28

- because cattle excreted / produced faeces - in field B crop used elements / minerals

Question 29

how can the chemical energy store in dry biomass by estimated

Answer 29

using calorimtery energy released = specifc heat capicity of water x volume of water (cm3) x temp increase of water

Question 30

populations of different species form a

Answer 30

community

Question 31

give 3 reason for the low effency of energy transfer from secondary consumers to tertiary consumers in an ecosystem (3)

Answer 31

heat loss from respiration food not digested not all eaten excretion

Question 32

suggest 2 reasons for conserving rainforests

Answer 32

protect species for biodoversty protect habitats reduce climate change source of medicine reduces erosion/ eutrophication

Question 33

farming cattle for humans to eat is less effective than farming crops because of energy transfer explain why (2)

Answer 33

energy lost between trophic levels energy lost via respiration/ excretion

Question 34

the chemical energy store in dry biomass can be estimated using....

Answer 34

calorimetry

Question 35

use your knowledge of NPP to explain why freshwater marshes have a high CUE (carbon use effecentcy) and the advantage of this.

Answer 35

low respiration less energy lost via respiration more growth/ biomass

Question 36

The student used the equation however she subsfrusted height for biomass. This was because she didn't want to destroy the plants to measure their biomass. State the assumptions the student has made and suggest why this might not be valid (2)

Answer 36

assumed that height is directly proportional to biomass height doesn't include the roots some increase in height because of water gain

Question 37

loss of nutrients into lake Malawi has resulted in a decrease in some fish populations explain why

Answer 37

algae bloom block light no photosyntjsis so plants die sarpobitic aerbocally respire less oxygen for fish to respire