Energy

It means changing energy into a form that can be used by organisms

Energy is fixed by autotrophs

• A photoautotroph is an organism that uses photosynthesis to convert light energy and inorganic molecules (H₂O and CO₂) into complex organic molecules eg glucose, starch, cellulose, etc.
• Examples of photoautotrophs are green plants eg daisy

• A chemoautotroph is an organism that uses the energy released from the breakdown of inorganic molecules to synthesise complex molecules
• Examples of chemoautotrophs are bacteria eg Nitrosomonas and Nitrobacter

• Primary productivity is the amount of material made by an autotroph in an ecosystem in a given time.
• It can be measure by the biomass of vegetation added to an ecosytem per unit area in a given time eg km²/m/year

• Gross Primary productivity is the total primary productivity.  Whereas, Net Primary Productivity is the gross primary productivity minus the energy used by the autotrophs during respiration.
• NPP = GPP - energy used in respiration

A producer is an organism that can synthesise it's own energy - they are autotrophs

A consumer is an organism that must eat other organisms to obtain their energy and nutrients - they are also called heterotrophs

An organism on the trophic level of an ecosystem where herbivores eat plants

An organism on the trophic level of an ecosystem where carnivores eat herbivores

An organism on the trophic level of an ecosystem where larger carnivores eat smaller carnivores

A herbivore is an organism that eats plants eg a sheep

A carnivore is an organism that eats other animals eg lion

An omnivore is an organism that eats both plants and animals eg humans

A detrivore is an organism that lives in or on the soil and feeds and gains nutrients from detritus eg worms

A decomposer is an organism that absorbs nutrients from dead organisms and waste from living organisms, converting them into inorganic molecules eg bacteria and fungi

A trophic level is any leve in a food chain or web which energy passes through as it goes through an ecosystem

• Producers convert light energy into chemical energy via photosynthesis.  They are the organisms that introduce the inital amount of energy that will pass through the ecosystem.
• Consumers pass this energy on through up the trophic levels of an ecosystem by eating animals.  Only ~10% of the energy is passed on to the next consumer as most is lost through heat.
• Decomposers break down the remains of dead plants and animals, releasing the leftover energy and nutrients back into the ecosytem so they can be used again.

~1%

~10%

Chemical energy

• Respiration (ultimately lost as heat)
• Movement
• Not all materials being consumed (bones)
• Not all materials being digested (poo)

As heat

In a pyramid of numbers each rectangle represents the number of organisms at each trophic level

In a pyramid of biomass each rectangle represents the (dry) mass of the organims at each trophic level

A pyramid of productivity shows the flow of energy through the food chain and the production or turnover of biomass at each trophic level

• Numbers - n/a
• Biomass - g/m²
• Producivity - g/m²/year or J/m²/year

• Pyramids of numbers can be inverted as one autotroph could provide enough energy to support numerous heterotrophs eg one tree can provide for many caterpillars
• Pyramids of biomass can be inverted as well as one autotroph, which can provide enough energy to support many heterotrophs, may have a smaller biomass than all the combined heterotrophs on the next trophic level eg one tree, many bugs
• However, a pyramid of productivity cannot be inverted as if the autotroph has a very small productivity it will not be making enough energy to support the heterotrophs on the following trophic levels

• Numbers - 'numbers' of organisms can be relatively easy to count
• Biomass - shows how much material is present which is a more accurate measure of energy than numbers
• Productivity - Takes account of the rate of production over a period of time (rather than a snapshot like biomass)

• Numbers - numbers do not represent all energy available eg one large producer
• Biomass - Does not take account of uneaten body parts, biomass is harder to measure than numbers, does not take into account fast reproducing producers which can sustain many primary consumers
• Productivity - Still need biomass and therefore need dry mass which destroys ecosystem