Energy Transfer and Productivity

What is the main way energy enters an ecosystem?

Photosynthesis

What do we call the organisms that photosynthesise?

Producers (they produce organic molecules using sunlight energy)

In what form do producers store energy?

Biomass

How is energy transferred in a food chain?

Biomass transfer = energy transfer

• energy transfers through organisms of an ecosystem when organisms eat other organisms

• producer eaten by primary consumer

• primary consumer eaten by secondary consumer

• secondary consumer eaten by tertiary consumer

What are the trophic levels?

• producer

• primary consumer

• secondary consumer

• tertiary consumer

How much energy is transferred from one trophic level to the other?

40%

Why is the energy transfer between trophic levels not 100% efficient?

• Plants can’t use all the light that they are exposed to (wrong wavelength, reflected, some passes through, some light hits parts that can’t photosynthesise

• Some parts of the eaten organism is not consumed (e.g. bones or roots) - they will go to decomposers

• Some of the organism consumed is indigestible so it will pass as waste - decomposers

Gross productivity

The energy taken in by a consumer (absorbed)

What happens to the energy taken in by the primary consumer?

• 30% is wasted to the environment through respiration for movement/body heat

• 10% of total energy available becomes stored as biomass and is passed on

What does it mean when energy is stored as biomass?

Energy is used for growth or it is stored as an energy unit

What is respiratory loss?

Energy lost due to respiration

Net productivity

Energy that is turned into biomass and available to the next trophic level

Equation for net productivity

net productivity = gross productivity - respiratory loss

How would you calculate the efficiency of energy transfer?

Net productivity over energy received x 100

Primary productivity

Gross net productivity - respiratory loss

the amount of energy producers give to the next trophic level

Gross primary productivity

The energy taken in by the producers from sunlight

How can we calculate the energy transfer between trophic levels?

• to find the energy in each trophic level measure the dry mass of the organisms

• energy is stored as biomass (water creates extra weight not to do with energy)

• find the amounts of each trophic level you are sampling (you are using grass from 1m^2 of land - find their dry mass

• dry the organism in an oven at a low temperature and regularly check the weight until the weight remains constant

• multiply dry mass by the size of the total population = total energy in organisms at that trophic level

• Find the difference in the energy from one trophic level to the next = energy transfer

• limitations - we don’t know if the consumers are consuming other producers so this may not be accurate

• to be accurate you must include all individual organisms at each trophic level