6.5.3 Efficiency of Energy Transfers Flashcards
Why is a large proportion of the suns energy not made available for photosynthesis?
A very large proportion of the Sun’s energy is not made available to photosynthetic plants, because
Light falls away from plants
Light passes through leaves or is reflected away
Light is a mixture of wavelengths, and only certain wavelengths stimulate photosynthesis
During photosynthesis, primary producers such as plants and algae convert light energy to chemical energy in biological molecules
The storing of this chemical energy as plant biomass makes a certain amount of energy available to the next trophic level, the primary consumers
Why does only a small percentage of plant biomass become biomass in the primary consumer?
Only a small percentage of plant biomass becomes biomass in the primary consumer because:
Not all the plant’s biomass is eaten by the primary consumer
Not all the consumer’s biomass intake is digested
Think about the energy content of cow dung, which can be dried and used as a heating/cooking fuel, as it contains a lot of undigested biomass e.g. cellulose
The primary consumer converts a lot of chemical energy to movement and heat, and only a small amount to new biomass in its own body
The efficiency of biomass transfer from one trophic level to the next is low, typically around 10%
How can you calculate efficiency of biomass transfers between trophic levels?
Given the appropriate data, it is possible to calculate the efficiency of biomass transfer from one trophic level to the next, as a percentage
Efficiency of transfer = (biomass transferred divided by biomass intake) cross times 100
Where:
Biomass transferred = biomass that has passed to the higher trophic level
Biomass intake = biomass of the lower trophic level that has been consumed
How can you calculate the efficiency of energy transfer between trophic levels?
A common way of working out the efficiency of energy transfer is calculating the net productivity of one trophic level as a percentage of the net productivity of the preceding trophic level
How can you find the net productivity of producers?
The net productivity of producers (also known as net primary productivity or NPP) can be calculated using the following equation:
NPP = GPP - R
Where:
GPP = gross primary productivity
R = respiratory losses
How can you find the net productivity of consumers?
The net productivity of consumers can be calculated using the following equation:
N = I - (F + R)
Where:
I = the chemical energy store in ingested food
F = the chemical energy lost to the environment in faeces and urine
R = the respiratory losses to the environment
How do human activities manipulate the transfer of biomass through ecosystems?
Human activity can adjust the efficiency of transfer of biomass between trophic levels, usually to maximise it in the context of maximising agricultural productivity
For producers, arable farmers can adopt these methods
Providing artificial light in greenhouses on overcast days
Optimising planting distances between crops
Irrigation to maximise growth in dry weather
Use of fertilisers
Selective breeding for fast growth
Use of fungicides/pesticides
Fencing to exclude grazers
Ploughing and herbicides to kill weeds
Plant crops that store energy in edible form e.g. seeds, fruit, tubers
Livestock farmers can adopt these methods for primary consumers (grazers)
Use of good quality feeds / food supplements
Use antibiotics and vaccines to reduce disease
Control predation with fencing or with indoor animal husbandry
Reduce competition for grazing e.g. rabbits, deer
Indoor husbandry to reduce energy loss from movement or from getting cold outside
