Energy transfer in ecosystems

What are producers

• In all ecosystems, there are producers - organisms that make their own food (plants)

  • During photosynthesis plants use energy (from sunlight) and carbon dioxide (from the atmosphere in land-based ecosystems, or dissolved in water in aquatic ecosystems) to make glucose and other sugars

What are some of the sugars produced during photosynthesis used for?

• Some of the sugars produced during photosynthesis are used in respiration, to release energy for growth

What is the rest of the glucose used for?

• The rest of the glucose is used to make other biological molecules, such as cellulose 

  • These biological molecules make up the plant’s biomass 

What is biomass

• Biomass can also be thought of as the chemical energy stored in the plant

• Biomass can be measured in terms of mass of carbon or the dry mass of tissue per given area 

What is dry mass?

• Dry mass is the mass of the organism with the water removed

Why is dry mass used not wet mass?

• The water content of living tissue varies so dry mass is used as a measure of biomass rather than wet mass

How can you estimate the amount of chemical energy stored in dry biomass

• You can estimate the amount of chemical energy stored in dry biomass by burning the biomass in a calorimeter. The amount of heat given off tells you how much energy is in it

  • Measured in joules or kilojoules

• Biomass can be measured in:

  • Kg m^-2

  • G m^-2

What is GPP

• Gross primary production (GPP)

  • The total amount of chemical energy store in plant biomass, in a given area or volume

What is NPP

• The chemical energy store in plant biomass after respiratory losses to the environment have been taken into account

  • The NPP is the energy available to the plant for growth and reproduction - the energy is stored in the plant’s biomass. It is also the energy available to other trophic levels in the ecosystem, such as herbivores and decomposers

What is the equation that links GPP to NPP

• GPP - R = NPP

  • R = Represents respiratory losses to the environment

How do consumers get energy?

• Consumers also store chemical energy in their biomass

  • Consumers get energy by ingesting plant material, or animals that have eaten plant material.

• Not all the chemical energy stored in the consumers’ food is transferred to the next trophic level. 

What factors contribute to energy losses at each trophic level?

• Not all solar energy is captured by leaves or is of the correct wavelength for photosynthesis

• Factors like water availability can limit photosynthesis

• Energy is lost during photosynthetic reactions

• Not all parts of biomass are edible or digestible by consumers

• Energy is lost as heat during movement or respiration

• Energy is lost in excretory materials, such as urine and faeces

What is the consumers net production

• The energy that’s left after all this is stored in the consumers’ biomass and is available to the next trophic level. This energy is the consumer’s net production

Ewuation for the net production of consumers

• N = I - (F + R)

  • N = Net production

  • I = Chemical energy in ingested food

  • F = Chemical energy lost in faeces and urine 

  • R = Energy lost through respiration

What is primary and secondary productivity

• The net production of consumers can also be called secondary production 

  • Primary and Secondary productivity is the rate of primary or secondary production 

  • It is measured as biomass in a given area in a given time e.g. kJ/m²/yr

How do you calculate how efficient energy transfer is from one trophic level to another

• To calculate how efficient energy transfer from on tropic level to another is:

  • Energy captured/total energy available  x100