Food Chains
Plankton -> Crustacean -> Fish -> Seal
- Every food chain starts with a PRODUCER- here it is plankton.
- The next organism is the PRIMARY CONSUMER- here it is Crustacean
- Next is the SECONDARY CONSUMER- here it is fish
- Then is it the TERTIARY CONSUMER- here it is the seal.
However, food chains are very oversimplified and don’t show enough detail
Food Webs
In IGCSE biology curriculum, a food web is more detailed as it has many food webs in together.
However, they are still too simple and they do not inform you about the numbers or mass of the organisms involved
Ecological Pyramids
In IGCSE biology, by definition, pyramid of numbers represent the numbers of organisms at each trophic level in a food chain. They have limitations because one tree has a lot of food on it.
Pyramid of Biomass: represent the total biomass of organisms at each trophic level. Biomass is the mass of biological material that makes up an organism.
Pyramids of numbers that involve trees are a little different than other pyramids of numbers because one tree can hold a lot of food, and therefore feed a lot of animals.
It is important to know that in IGCSE Biology, the Biomass of organisms get less at each level because:
- Some parts cannot be eaten (i.e. animal bones)
- Some parts cannot be digested or absorbed so are passed out as faeces.
- Some of the food is broken down and excreted as waste (i.e. urea)
- Some of the food is respired and used to release energy for the cells
- Only a small part of food is used to produce growth (10%)
Energy Transfers
Only energy that is used for growth can be passed on to the next trophic level or decomposers. Energy used as any other processes will eventually be transferred to the environment as heat. This limits the number of trophic levels as it will eventually have such a small energy content that it will not be worth hunting and eating.
End of this topic!
Drafted by Gina (Biology)