Energy flow
1.
The diagram shows what happens to each 1000 kJ of light energy absorbed by plants growing in a
meadow.
(a)
Use the information from the diagram to calculate
(i)
how much energy was transferred to herbivores.
(2 marks)
______________________________________________________________________
(ii)
the percentage of the energy absorbed during photosynthesis that was eventually
transferred to carnivores. Show your working
(2 marks)
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
(b)
The table gives the energy output from some agricultural food chains.
Explain why the food chain cereal crop  humans gives far more energy than the other two
food chains.
(3 marks)
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
2.
A scientist estimated the total amount of energy flow through each trophic level in a woodland per
year. The results were:
Energy absorbed by trees 4 600 000 kJ per m2 per year
Energy in sugar produced by trees 44 000 kJ per m2 per year
Energy transferred to primary consumers 2 920 kJ per m2 per year
Energy transferred to secondary consumers 700 kJ per m2 per year
(a)
Calculate the percentage of the energy absorbed by the trees that is transferred to sugar by
photosynthesis. Show your working.
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
(b)
Suggest two reasons why a large proportion of the energy is not transferred to sugar. (2 marks)
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
(c)
Give three reasons why some of the energy in the primary consumers is not passed on to the
secondary consumers.
(3 marks)
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
____________________________________________________________________________
3.
The diagram shows the amounts of energy that are transferred, over a period of time, through some
living things in a grassland habitat.
(a)
Calculate the amount of energy transferred from the grass to the cows.
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
(b) X is a process in plants.
(i)
Calculate the amount of energy usefully transferred by process X.
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
(ii)
Name process X.
(1 mark)
____________________________________________________________________________
(c)
Give two ways in which energy is ‘lost’ from the cows at Y.
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
4.
Distinguish between gross primary productivity and net primary productivity.
marks)
(2
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
5.
Explain why food chains are limited to a maximum of five levels.
(4 marks)
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Energy flow
1.
The diagram shows what happens to each 1000 kJ of light energy absorbed by plants growing in a
meadow.
(c)
Use the information from the diagram to calculate
(i) how much energy was transferred to herbivores.
(2 marks)
200 + 600 = 800
1000-800 = 200KJ
(ii) the percentage of the energy absorbed during photosynthesis that was eventually
transferred to carnivores. Show your working
(2 marks)
20/1000 = x100 = 2%
(iii)
The table gives the energy output from some agricultural food chains.
Explain why the food chain cereal crop  humans gives far more energy than the other two
food chains.
(3 marks)
energy lost by animal (pig / cattle)
extra stage
extra trophic level in waste materials e.g. in muscular activity
movement in keeping body temperature higher than surroundings
lost as heat
2.
A scientist estimated the total amount of energy flow through each trophic level in a woodland per
year. The results were:
Energy absorbed by trees 4 600 000 kJ per m2 per year
Energy in sugar produced by trees 44 000 kJ per m2 per year
Energy transferred to primary consumers 2 920 kJ per m2 per year
Energy transferred to secondary consumers 700 kJ per m2 per year
(a)
Calculate the percentage of the energy absorbed by the trees that is transferred to sugar by
photosynthesis. Show your working.
(2 marks)
44000 / 4600000 = x100 = 0.956%
(b)
Suggest two reasons why a large proportion of the energy is not transferred to sugar. (2 marks)
heats up leaves
wrong wavelength colour
absorbed by non-photosynthetic parts
transmitted through leaves
reflected off leaves
(c)
Give three reasons why some of the energy in the primary consumers is not passed on to the
secondary consumers.
(3 marks)
respiration of primary consumers
movement of primary consumers
waste from primary consumers
repair/growth of primary consumers
heat losses to surroundings
3.
The diagram shows the amounts of energy that are transferred, over a period of time, through some
living things in a grassland habitat.
(a) Calculate the amount of energy transferred from the grass to the cows.
1020 + 1910 + 130 = 3060KJ
(2 marks)
(b) X is a process in plants.
(i)
Calculate the amount of energy usefully transferred by process X.
(2 marks)
3060 + 15000 + 4000 = 22060KJ
(iii)
Name process X.
(1 mark)
Photosynthesis
(c)
Give two ways in which energy is ‘lost’ from the cows at Y.
(2 marks)
faeces
urine
6.
Distinguish between gross primary productivity and net primary productivity.
marks)
(2
Gross Primary Productivity (GPP) is the total amount of energy captured by producers (such as
plants) through photosynthesis in an ecosystem.
Net Primary Productivity (NPP) is the energy remaining after producers use some for respiration; it
represents the energy available to herbivores and higher trophic levels
7.
Explain why food chains are limited to a maximum of five levels.
(4 marks)
Due to energy loss at each level.
According to the 10% Rule, only about 10% of the energy from one trophic level is passed to the
next,
while the rest is lost as heat through metabolism, respiration, and waste.
As energy decreases with each step, higher trophic levels receive insufficient energy to support
additional levels, making food chains short, usually 3–5 levels at most