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Food chains

What feeding relationships are shown here?


Feeding relationships


Energy transfer in the food chain


Why aren’t food chains very long?

This tiger is a top predator; the final level in a food chain.

Energy is lost at all levels in food chains. Animals at the top

of a long food chain would not get enough energy to survive.

Most food

chains only

contain four or

five species,

why is this?


Food chains and pyramids

What can pyramids show about energy transfer?


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 specified area.

What are pyramids of numbers?


Numbers or biomass?


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

the number of organisms at each trophic level in a

specified area.

As a single tree can support many organisms, this

food chain produces an unbalanced pyramid.

Understanding pyramids of numbers


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.


Food chains and pyramids


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?


A luxury item?

An 800g loaf of bread costs

£0.80.

A 400g steak costs

£4.00.

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

This equals £1.00 per 100g. This equals £0.10 per 100g.

Why is meat more expensive than bread?


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.


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?


Energy loss in food chains


Why do 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?


How do you calculate efficiency?

Energy efficiency can be calculated using the following

equation:

=efficiencyenergy used for growth (input)

energy supplied (output)

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%


Energy efficiency calculations


Why is maximizing yields important?

Many farmers use intensive farming methods to maximize

their yields. Why do they do this?

In what ways can farmers maximize their yields?

Increased energy

efficiency.

Lower costs for

farmers.

Cheaper food for

consumers.

More food produced

in the same amount

of space.


How do greenhouses increase yields?

Greenhouse operators raise their yields and profits by

maximizing photosynthesis and controlling other factors.

What factors would you

need to control to get

the maximum yields

from photosynthesis?

light levels

carbon dioxide

temperature.

Products can be grown earlier in the year and in conditions

in which they would not normally grow.


Controlling growth in a greenhouse


How can losses be reduced?

Not all of a crop planted will be harvested. What happens to

the rest?

What chemicals are used to cut competition?

Herbicides are used to kill weeds, and pesticides are used

to kill pests, such as insects and fungi.

58% harvested

13% lost to

disease

13% lost

to pests

16% lost

to weeds


The right chemical for the job


What is hydroponics?

Many salad crops,

including tomatoes,

lettuces and cucumbers,

are grown in this way.

Hydroponics is a technique used to grow plants without soil.

The plants gain all their nutrients and minerals from

specially-treated water circulating around their roots.

Other conditions, such

as the levels of light

and carbon dioxide, are

also closely controlled.

In what conditions would hydroponics be useful?


Why use hydroponics?

There are many advantages of using hydroponics.

These include:

Lower risk of crops becoming diseased

from soil-based pathogens and pests.

Fewer weeds.

A reduced need for

pesticides and herbicides.

Crops can be grown in places with

poor soil or little water for irrigation.

However, hydroponics requires expensive equipment and

technical knowledge and so will not be suitable for all

situations.


The transfer of biomass and energy in aquatic food chains

can be very efficient. Why is this?

Why are aquatic food chains efficient?

The organisms do not thermoregulate, so they use less

energy for respiration.

Very little phytoplankton escapes being eaten so

decomposers take less of the energy.

What could reduce the number of large fish caught?


Can fish be farmed?

Most of the salmon and trout eaten in this country comes

from fish farms. The fish are reared in giant tanks or cages.

Put yourself in charge. What could you do to make sure

you raised the biggest possible yield of fish?


Increasing yields in fish farms


How can livestock be farmed efficiently?

The efficiency of meat

production increases if

animals are kept at a

constant temperature and

their movement is restricted.

Is efficiency always the most important consideration?

They can also be fed

concentrates – food that

leaves very little waste –and given antibiotics to

combat infections.

Chickens and pigs lose energy through movement and

thermoregulation. How could a farmer increase the yield of

meat from livestock?


What are the problems of livestock farming?

To help prevent these problems, farmers must comply

with EU regulations, but some people do not think these

regulations are strict enough.

If animals are kept in extremely cramped conditions, they

may start to develop abnormal behaviour.

Animals are also more likely to

catch diseases if they are

living in a cramped, enclosed

environment.

For example, chickens may

pluck out each other’s feathers.


Intensive farming and the environment

Intensive farming must be well managed to prevent

environmental problems. These include problems include:

Pollution of water supplies

by animal waste.

Accumulation of pesticides

in food chains.

Eutrophication of rivers and

lakes due to inappropriate

use of artificial fertilizers.

Destruction of wildlife

habitat for agricultural land.

Depletion of soil minerals.


Citizens’ panel


How do we use biomass?

Biomass supplies us with more than just food.

How can biomass be used by humans?


Uses of biomass


What is biomass energy?

Biomass energy is one of the oldest forms of energy.

The biomass stored in

wood can be burned for

heating and cooking.

Animal dung can also

be burned for energy.


Biodiesel and bioethanol

Could biomass fuels replace petrol?


Bioethanol is produced

by fermenting the

carbohydrates in sugar

beet/cane or wheat

crops.

Biodiesel is produced by

chemically reacting

vegetable oils or animal

fats with alcohol and a

catalyst. This bus runs on

biodiesel made from

soya beans.

Biomass can be used to make biodiesel and bioethanol.

How can biomass be used for fuel?


More than our fair share?

Biofuels have many advantages but using land to grow

fuel reduces the area available for food crops.

Humans take the biggest

slice of the Earth’s resources, using about

40% of the biomass

produced on land.

How would growing

biofuels affect this?

Should humans leave

more biomass for other

organisms?


http://www.photos.com/en/search/close-up?oid=5078679&hoid=6a1367ffd25aa8489484e4f77129d677

http://www.photos.com/en/search/close-up?oid=5078679&hoid=6a1367ffd25aa8489484e4f77129d677


Glossary (1/2)

biomass – The organic material that makes up plants and

animals.

carnivore – An organism that only eats other animals.

consumer – An organism that feeds on plants or animals.

fertilizer – A mixture of mineral salts needed to support

plant growth.

food chain – A sequence that shows feeding relationships

and the transfer of energy between organisms.

herbivore – A organism that only eats plants.

hydroponics – Growing plants without using soil.


Glossary (2/2)

omnivore – An organism that eats both plants and

animals.

pyramid of biomass – A scale drawing that illustrates

the biomass present at each stage of a food chain.

pyramid of numbers – A scale drawing that illustrates

the number of organisms present at each stage of a food

chain.

producer – A plant that makes food by photosynthesis.

respiration – A series of reactions that releases energy

from organic molecules in both plants and animals.

trophic level – A feeding level in a food chain.


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