Trophic Levels & Decomposers & Pyramids of Biomass & Energy Transfer

What is a trophic level?

An organism's feeding position in a food chain.

What is trophic level 1?

Producers — plants and algae.

What is trophic level 2?

Primary consumers — herbivores that eat producers.

What is trophic level 3?

Secondary consumers — carnivores that eat herbivores.

What is trophic level 4?

Tertiary consumers — carnivores that eat other carnivores.

What is an apex predator?

A carnivore with no predators.

What do decomposers do?

They break down dead plant and animal matter.

How do decomposers feed?

They secrete enzymes into the environment, digesting dead material externally. Small soluble food molecules then diffuse into the microorganism.

What does a pyramid of biomass show?

The relative amount of biomass at each trophic level of a food chain.

Which trophic level goes at the bottom?

Trophic level 1 — producers.

Why do biomass pyramids normally get narrower at higher trophic levels?

Only a small proportion of biomass is transferred from each trophic level to the next.

What must you do when constructing a pyramid of biomass?

Draw bars with widths proportional to the biomass at each trophic level, with producers at the bottom.

Approximately what percentage of incident light energy do producers transfer for photosynthesis?

About 1%.

Approximately what percentage of biomass is transferred from one trophic level to the next?

About 10%.

Why isn't all biomass transferred to the next trophic level?

Not all parts of an organism are eaten. -- Not all ingested material is absorbed; some is egested as faeces. -- Some absorbed material is lost as waste, including urea in urine. -- Large amounts of glucose are used in respiration, producing carbon dioxide and water rather than new biomass.

Why are there fewer organisms at higher trophic levels?

Biomass is lost at each trophic level, so less biomass/energy is available to support organisms at the next level.

What is the equation for efficiency of biomass transfer?

Efficiency = (biomass transferred to next level / biomass available at previous level) x100

If transfer efficiency and starting biomass are given, how do you calculate transferred biomass?

Transferred biomass = starting biomass x (efficiency / 100)