A Trophic level is a feeding level. Trophe is a greek word for nourishment.
The amount of energy, biomass, and usually the number of organisms all decrease as you move up a trophic level.
Bars of the Pyramid of biomass
Each bar shows the mass of living material at that stage of the food chain (how much all the organisms would weigh if you put them altogether)
Almost always a pyramid shape as biomass is lost at each stage in the food chain.
To construct a pyramid of biomass you use the DRY BIOMASS
DRY BIOMASS- you dry out all the water from the organism before weighing them.
Can be difficult as you have to kill the organism to work it out. (unethical to kill lots of animals each time you work it out)
Difficulties in construction
Some organisms feed at more than one trophic level
Pyramid of numbers
Each bar shows the number if organisms at that stage of the food chain instead of their mass.
They can be any shape not just Pyramid.
For example a pear tree bar many be smaller than an aphids bar as one pear tree can feed a huge number of aphids.