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Biomass
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Competition –
Who will finish first?
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Herbivore

Consumer

Carnivore

Producer

Omnivore

Mass

Weight
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Definition:
 the
total mass of living matter in a given
unit area
 The
total amount of living material in a
given habitat, population, or sample
 Specific
measures of biomass are
expressed in dry weight (after removal of
all water from the sample)
 It’s
measured in kilograms (kg)
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Food Chains
Food chains commonly have four links but seldom more than six.
In food chains the arrows go from food to feeder.
In other words the arrows mean ‘eaten by’
Producer
Herbivore
Carnivore
Top
carnivore
Examples of food chains include:
Grass
Rose bush
Squirrel
Beetles
Racoon
Shrew
Cougar
Wolf
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Complete Aquarium
ecosystem
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Complete –
Energy Transfer
Pyramids of Numbers

Energy is passed along food chains

The number of organisms decreases as you go from one
trophic level to the next.

This is because most of the energy is lost as you go from one
level to the next in a food chain.
Pyramids of Numbers




Just staying alive uses up most of the food energy that’s ‘acquired’
by a consumer.
Its needed for moving, growing and keeping warm.
Not all of the material from each level is eaten.
The food energy only passes along the food chain when its eaten
by a consumer from the next level up.
Pyramids of Numbers
 Pyramids
of numbers can look weird.
 This
is because an oak tree is very large compared to
the caterpillar.
 There
is only 1 oak tree but 1000’s of leaves for the
caterpillars to feed on.
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Pyramids of Biomass

Pyramid of numbers looks weird because it doesn’t
take into account the mass of the oak tree.

If the pyramid represented the total mass of the
organisms at each level it would look more like a
pyramid.

It would then be a pyramid of biomass.
Robins (10 kg)
Caterpillars (20 kg)
Oak Tree (10,000kg)
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Complete:
 Produce
a pyramid of numbers and then a pyramid
of biomass using this data.
10 cabbages
250 caterpillars
5 thrushes
1 sparrow hawk
 Use
graph paper, colour pencils and a ruler.
 What
do you notice about the pyramids?
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Energy Flow
So: in a food chain, usually only 1% to 10% of the biomass (energy)
in one feeding level is passed on to the next feeding level
Assuming only 10% of the biomass is passed on at each stage of the
following food chain, calculate the biomass at each successive feeding
level
Top
carnivore
6.6
Carnivores 66
Herbivores
Producers
660
6,600
Figures show dry mass in grammes per square metre
Thus at each stage of a food chain, less material and less energy are contained
in the biomass of the organisms. This means that the efficiency of food
production can be improved by reducing the number of stages in the food
chains involved, so that less biomass is lost
Food chains involved in feeding humans:
Cereals
human
Grass
sheep
Algae
mayfly larvae
human
pond skater (insect)
trout
human
Which of the above food chains is most efficient at getting biomass to
humans?
‘Cereals to humans’ is most efficient, because it has least stages (one) to
lose biomass
‘Algae to humans’ is least efficient, because it has most stages (four) to lose
biomass
To sum up: the amounts of the material and energy contained in the biomass of
organisms is reduced at each successive stage in a food chain because:
Some materials and energy are lost in the organism’s waste materials
(excretion) or via undigested or indigestible (defaecation);
The heat losses are especially large in mammals and birds whose
bodies must be kept at a a constant temperature which is usually
higher than that of their surroundings
Energy Flow
So the efficiency of food production in food animals, (for example,
chickens, turkeys, sheep, pigs, cattle), can be improved by:
Restricting energy loss from food animals by limiting their movement;
By controlling the temperature of their surroundings so that they do not lose
biomass trying to keep warm