Trophic Levels & Biomass

What is biomass?

The mass of living material in organisms.

What is a trophic level?

An organism's feeding position in a food chain.

Which organisms occupy trophic level 1?

Producers.

Which organisms occupy trophic level 2?

Primary consumers.

Which organisms occupy trophic level 3?

Secondary consumers.

Which organisms occupy trophic level 4?

Tertiary consumers.

How do producers increase their biomass?

They use photosynthesis to make organic molecules.

How do consumers increase their biomass?

They eat other organisms and incorporate some of the material into their own tissues.

Why is biomass transferred between trophic levels?

Organisms consume material from organisms at lower trophic levels.

What is a pyramid of biomass?

A diagram showing the biomass present at each trophic level.

What does the width of each bar in a pyramid of biomass represent?

The amount of biomass at that trophic level.

Why are pyramids of biomass usually narrower at higher trophic levels?

Not all biomass is transferred to the next trophic level.

Why is biomass often measured as dry mass?

Water content varies and does not represent stored organic material in the same way.

What is dry biomass?

The mass of biological material after water has been removed.

Why are producers essential for most food chains?

They convert light energy into chemical energy stored in organic biomass.

Why can a food chain contain only a limited number of trophic levels?

Biomass transfer is inefficient, leaving insufficient biomass to support many higher levels.

Why do organisms at higher trophic levels generally have less available biomass?

Material is lost from the food chain at each transfer.

What is the difference between a pyramid of biomass and a pyramid of numbers?

Biomass pyramids show mass of organisms, while numbers pyramids show numbers of individuals.

Why might a pyramid of numbers have an unusual shape?

A single large producer, such as a tree, may support many consumers.

Why does a pyramid of biomass give more information than a pyramid of numbers?

It accounts for organism size and total living material.