1. Energy Transfer In Food Chains
Noadswood Science, 2011

2. Energy Transfer In Food Chains
Monday, April 10, 2017
Energy Transfer In Food Chains
To understand how energy is transferred in food chains

3. Food Chains A food chain shows what eats what in a particular habitat
For example, grass seed is eaten by a vole, which is eaten by a barn owl – the arrows between each item in the chain always point in the direction of energy flow (from the food to the feeder)

4. Energy Origins Where does the energy for a food chain originate from?
The Sun is the ultimate source of energy for most communities of living things – green plants absorb some of the Sun’s light energy to make their own food by photosynthesis
The other organisms in a food chain are consumers, because they all get their energy and biomass by consuming (eating) other organisms

5. Limited
Energy is transferred along food chains from one stage to the next, but not all of the energy available to organisms at one stage can be absorbed by organisms at the next one
The amount of available energy decreases from one stage to the next – some of the available energy goes into growth and the production of offspring, and this energy becomes available to the next stage, but most of the available energy is used up in other ways: -
Energy released by respiration is used for movement and other life processes, and is eventually lost as heat to the surroundings
Energy is lost in waste materials, such as faeces
All of the energy used in these ways returns to the environment, and is not available to the next stage

6. Food Chain
Food chains are never very long (usually only 4/5 stages at most) – why is this?
Remember the arrow shows the energy being transferred from one organism to the next - between each step energy is lost in a variety of ways, including: -
Growth of the organism
Respiration
Reproductive costs
Lost through waste products (poo)
Lost through heat
This is why food chains are never that long - as lots of energy is lost from one stage to the next

7. Food Chain

8. Food Web
In most habitats organisms normally eat / are eaten by more than one other organism
To represent this we use food webs (like food chains but they interlink with one another), e.g. a pond
Here the producers are the pondweed and the microscopic algae
Mayfly nymphs eat the pondweed and microscopic algae, and freshwater shrimp eat the microscopic algae
Dragonfly nymphs and brown trout eat the mayfly nymphs and freshwater shrimp
Brown trout also eat the dragonfly nymph!

9. Key Words Producers – green plants make food by photosynthesis
Primary consumers – usually eat plant material (they are herbivores)
Secondary consumers – usually eat animal material (they are carnivores)
Predators – kill for food (they are either secondary or tertiary consumers)
Prey – the animals that predators feed on
Scavengers – feed on dead animals
Decomposers – feed on dead and decaying organisms, and on the undigested parts of plant and animal matter in faeces

10. Balance
Populations in a food chain are dependent upon one another – there is a balance between the producers and consumers in the food chain
For example if there are lots of giraffes they will eat a large quantity of the trees and shrubs until there may be insufficient amounts to support them. If this is the case many will begin to starve and die
Fewer giraffes means less food for lions, which will eventually see a population decrease
Less giraffes will allow more shrubs and tress to survive, so the giraffe population recovers, leading to the lion population recovering, until the process repeats itself…

11. Efficiency
This animal has eaten 100 kJ of stored energy in the form of grass, and excreted 63 kJ in the form of faeces, urine and gas
The energy stored in its body tissues is 4 kJ – how much has been used up in respiration?
How much energy is passed on (energy efficiency percentage)

12. Efficiency = (4KJ ÷ 100KJ) × 100 = 4%
This animal has eaten 100 kJ of stored energy in the form of grass, and excreted 63 kJ in the form of faeces, urine and gas
The energy stored in its body tissues is 4 kJ – how much has been used up in respiration?
Energy taken in = 100KJ
Energy transferred to tissues + faeces etc… = 63KJ + 4KJ = 67KJ
Energy released by respiration = 100KJ – 67KJ = 33KJ
Only 4 kJ of the original energy available to the animal is available to the next stage – the efficiency of this energy transfer is: -
Efficiency = (4KJ ÷ 100KJ) × 100 = 4%

13. Energy Transfer Question
What do plants use a lot of their energy for?
Do all organisms loose the same amount of heat energy?
Why doesn’t the whole of an organisms body get passed to the next stage of the food chain?
Food chains are rarely more than 5 trophic levels, why?
What happens to the energy lost in animal waste?
Why is food production more efficient with less stages in the food chain?
Explain using pyramids of biomass why it would be better to eat less meat and more plants with an increasing population

14. Energy Transfer Answers
What do plants use a lot of their energy for?
To make new cells
Do all organisms loose the same amount of heat energy?
No warm blooded animals loose more as their body has to be kept at a constant temperature
Why doesn’t the whole of an organisms body get passed to the next stage of the food chain?
Some of it is inedible or can’t be digested e.g. bones and teeth, fibre and cell walls
Food chains are rarely more than 5 trophic levels, why?
So much energy is lost at each stage that there is not enough left to support the organisms after 4 or 5 stages

15. Energy Transfer Answers
What happens to the energy lost in animal waste?
It is recycled in the soil and eventually new plants will use it
Why is food production more efficient with less stages in the food chain?
Less material and less energy is wasted this means more food can be produced
More food would be made as less energy is lost, so in the limited land space enough food would be made to go around