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Page 1: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

© Boardworks Ltd 20111 of 27

Energy Transfers in Food Chains

Page 2: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Page 3: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Feeding relationships

Page 4: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Energy transfer in a food chain

Page 5: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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The length of food chains

This tiger is a top

predator – the final level

in a food chain.

Most food chains only

contain four or five

species, or less.

Why is this?

Firstly, plants cannot actually absorb all of the energy from

the Sun. Furthermore, energy is lost at all levels in

food chains. If a food chain was very long, animals at the top

of it would not get enough energy to survive.

Page 6: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Page 7: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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What can pyramids show about energy transfer?

Food chains and pyramids

Page 8: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Pyramids of numbers only give an accurate impression of

the flow of energy in a food chain if the organisms are of

similar size. Measuring the biomass at each trophic level

can give a more accurate picture.

Pyramids of numbers are a quantitative way of

representing food chains.

What are the problems of

representing food chains in

pyramids of numbers?

They record the number of

organisms at each trophic level

in a food chain.

What are pyramids of numbers?

Page 9: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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In a pyramid of numbers, the length of each bar represents

the number of organisms at each trophic level in a

food chain.

As a single tree can support many organisms, this food chain

produces an unbalanced pyramid.

Understanding pyramids of numbers

Page 10: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Understanding pyramids of biomass

In a pyramid of biomass, the length of each bar represents

the amount of organic matter – biomass – at each trophic

level in a specified area.

At each trophic level, the amount of biomass and energy

available is reduced, giving a pyramid shape.

Page 11: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Constructing pyramids

Page 12: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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The problem with pyramids

Pyramids are a very simplified way of representing

food chains.

Some animals may belong to more than

one trophic level. For example, humans are

often primary, secondary and even tertiary

consumers. There would be no way to show

this properly with either form of pyramid.

It is also very difficult to accurately measure the biomass of

an ecosystem. This is done by sampling the biomass, and

then drying it out. While it may be possible to dry and weigh

some plants, there are ethical issues with doing the same

thing to animals – especially endangered species.

Page 13: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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Food chains and pyramids

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What are the benefits of eating plants?

Your friend is at university and has phoned you to

complain that all she can afford to eat is beans on toast.

How could you make her

feel better about her diet?

What are the energy

arguments for eating a

plant-based diet?

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A luxury item?

How can the costs of these food items be compared fairly?

Why is meat more expensive than bread?

A 400g steak costs £4.00.

This equals £1.00 per 100g.

An 800g loaf of bread

costs £0.80.

This equals £0.10 per 100g.

Page 17: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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How energy efficient is it to eat meat?

Food chains can be used to understand why some foods cost

more than others. Which of these chains is the most efficient?

The first food chain is the most efficient because it

contains fewest trophic levels, so less energy will be lost.

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Is eating meat less energy efficient?

Cattle and other livestock are fed grain and cereals.

Would it be more energy efficient if humans ate the plant

crops instead?

If a one-acre field of corn is

used to feed cows, it can

support one person.

If the same area is used to

feed humans directly, it can

support 10 people.

Why is so much energy lost?

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Energy loss in food chains

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Some animals need more energy

Mammals and birds are able to

regulate their body temperature.

This has many advantages but it

uses lots of energy.

Other animals, such as

snakes, lizards and fish,

are unable to regulate their

body temperature, so need

less energy.

Would it be more energy

efficient to farm snakes for

food than chickens?

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What happens to the waste?

Page 22: Energy Transfers in Food Chains - todhigh.comtodhigh.com/.../03/Energy_Transfers_in_Food_Chains.pdf · The length of food chains This tiger is a top predator –the final level in

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How do you calculate efficiency?

Energy efficiency can be calculated using the following

equation:

=efficiencyenergy used for growth (output)

energy supplied (input)

For example, if grass receives 1,000,000kJ of energy from

the Sun and uses 20,000kJ of energy for growth, then:

efficiency =1,000,000 kJ

20,000 kJ

= 0.02 = 2%

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Energy efficiency calculations

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Glossary

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Anagrams

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Multiple-choice quizMultiple-choice quiz