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TRANSCRIPT
6 of 48 © Boardworks Ltd 2007
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?
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Food chains and pyramids
What can pyramids show about energy transfer?
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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 specified area.
What are pyramids of numbers?
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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
specified area.
As a single tree can support many organisms, this
food chain produces an unbalanced pyramid.
Understanding pyramids of numbers
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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.
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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?
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?
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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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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?
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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%
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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.
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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.
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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
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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?
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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.
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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?
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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?
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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?
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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.
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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.
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How do we use biomass?
Biomass supplies us with more than just food.
How can biomass be used by humans?
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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.
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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?
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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?
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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.
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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.