Today we are covering from the specification:

Starter: Can you determine the number of kilowatt-hours of electricity a student would receive if

the efficiency of transfer in the following flow were only 10%:

10,000 kWh from a power plant transformer home student’s room student’s

computer

The result: 1 kWh available for the student’s use.

How much of the sun’s radiation (solar or light energy) is captured

by a plant or algae? Why?

6CO2 + 6H20 C6H12O6 + 6O2

1-3%

5 of 31 © Boardworks Ltd 2009

Energy availability in photoautotrophs

Energy losses in food chains• Over 90% of the sun’s energy is reflected

back into space by clouds and dust or absorbed by the atmosphere.

• Not all wavelengths of light can be absorbed and used for photosynthesis

• Light may not fall on a chlorophyll molecule• A factor, such as low carbon dioxide levels,

may limit the rate of photosynthesis

Energy losses in food chains• The total quantity of energy that the plants in a

community convert to organic matter is call gross production.

• Plants use 20-50% of this organic matter as respiration, leaving little to be stored. The rate at which they ‘store energy’ is called the net production.

Net production = gross production – respiratory losses

Energy losses in food chains

• Only 10% of this food stored is used by primary consumers for growth.

• Secondary and tertiary consumers are more efficient transferring about 20% available from the prey into their bodies.

• Why?

Energy losses in food chains1. Some parts of the organism not eaten2. Some parts are not eaten but cannot be digested

and are therefore lost in faeces3. Some of the energy is lost in excretory materials,

such as urine4. Some energy losses occur as heat from

respiration, directly from the body to the environment.

Why would energy losses be higher in birds and mammals compared to reptiles/amphibians?

Stoat

Toad

Caterpillar

Grass

1. Limits to 4/5 organisms because insufficient energy is available to support a large enough breeding population at trophic levels higher than these

2. Total mass of organisms in a particular place (biomass) is less at higher trophic levels

3. Total amount of energy stored is less at each level as one moves up a food chain

How does the relative inefficiency of energy transfer between trophic levels affect food chains?

Trophic level

Calculating the efficiency of energy transfers

• Data are often presented showing the amount of energy available at each trophic level.

• The amount of energy available is usually measured in kilojoules per square metre per year (kJ m-2year-1)

• It is useful to calculate the efficiency of the energy transfer between each trophic level.

• We are going to calculate energy transfers in different ecosystems:

Calculating the efficiency of energy transfers

Energy transfer = energy available after the transfer x 100 energy available before the transfer

Energy transfer between trophic levels

About how energy moves and is lost between trophic levels

WAL:

All

Most

Some

• How is energy lost along a food chain? Why do most food chains have no more than 5 trophic levels

• How is the percentage efficiency of energy calculated?

•What percentage of energy is transferred from one level to the next?

5,4,3,2,1 go… can you talk about food chains and food webs for 60 seconds mentioning as many as the key words

as possible?Producer Consumer

Food chain

Food web

Omnivore

Habitat

Trophic level

Energy loss

Heat

Quarternary

Decomposer

Respiration

Tertiary consumer

Secondary consumer

Primary consumer Detritivore

CarnivoreHerbivore