02/03/2019
Efficiency of Biomass Transfer
Learning Objectives:
• Describe how biomass is lost
between trophic levels.
• Calculate the efficiency of biomass
transfer.
• Explain why the number of trophic is
limited
Key Words:
Efficiency, Biomass, Trophic Level,
Producer, Consumer
Starter:
• Where does all the energy within a
food web come from?
• Name the 7 abiotic factors that
affect and ecosystem.
• What are the three types of
interaction between populations
within a community?
• Why are pyramids of numbers
often inverted?
• Why are food chains mostly limited
to a quaternary consumer?
Starter Answers:
• Where does all the energy within a food web come from?
The Sun.
• Name 7 abiotic factors that affect and ecosystem.
Temperature, light, Moisture level, soil pH, Oxygen levels, Pollution and available
nutrients.
• What are the three types of interaction between populations within a
community?
Predation, Mutualism, Parasitism.
• Why are pyramids of numbers often inverted?
They don’t take into account the mass of the organisms.
• Why are food chains mostly limited to a quaternary consumer?
As energy transfer up food chains is very inefficient,
Pyramids of Biomass
0.5 Kg
Sparrowhawk
5 Kg
Bluetits
50 Kg
caterpillars
500 Kg
leaves
1 Square = 25 Kg
Pyramids of Biomass
Think, Pair, Share: Why do you think that biomass is lost at each stage?
• Not all organisms are eaten at the stage above.
• Once eaten, some material is passed out as waste
and so not all energy is absorbed.
• Energy is used for respiration by an organism, this
is used for movement and living process, it is
eventually lost as thermal energy to heat the
surroundings and so is not passed on.
Plant based diets
• Vegetarianism and veganism
are growing in popularity.
• Often because of how animals
within the food industry are
treated.
• But can you think of an energy
argument for eating a plant
based diet?
• What are some of the issues
that could arise from having a
plant based diet?
Food Prices
• A 400g steak costs £4.00.
• An 800g loaf of bread costs £0.8
Why do you think steak costs
so much more than bread.
Food Prices
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.
Food Prices
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.
Energy loss in food chains
Energy loss in food chains
Energy Loss in Animals
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?
Calculating Efficiency
Energy efficiency can be calculated using the
following equation:
efficiency =
energy used for growth (input)
energy supplied (output)
* 100
For example, if grass receives 1,000,000 kJ of
energy from the Sun and uses 20,000 kJ of energy
for growth, then:
Efficiency = 20,000 / 1,000,000 = 0.2
Efficiency = 0.2 * 100 = 2% Efficient
Energy efficiency calculations