Topics 3.3 and 3.4

By: Alejandro Gutiérrez & Alejandro Garza

Food chain The energy passes through an ecosystem along a food chain

Food chain: Series of steps in which organisms transfer energy by eating and being eaten. They vary in length.

Food web In most ecosystems, feeding relationships

are much more complicated than the relationships described in a single, simple chain.

A food web is a complex network of feeding interactions.

Food web

Disturbance in food webs

The balance of a food web is very delicate, and any disturbance may ocassion a change in it.

For example, in case of oil spill, it would affect the number of bacteria and fungi, and these are the ones that break down detritus, ocassionating further changes.

Trophic leves and ecological pyramids

Trophic level: Each step in a food web.

Ecological pyramid: Shows the relative amount of energy or matter contained within each trophic level in a given food chain or food web. There are 3 types: Pyramids of energy, pyramids of biomass, and pyramids of numbers.

Pyramids of energy

Show the relativa amount of energy available at each trophic level of a food chain or web.

Pyramids of Biomass

Biomass: Total amount of living tissue within a given trophic level.

Illustrates the relative amount of living organic matter available at ech trophic level in an ecosystem.

Pyramid of numbers

Shows the relative number of individual organisms at each trophic level in an ecosystem.

Biogeochemical cycles

Unlike the one-way flow of energy, matter is recycled within and between ecosystems. Elements pass from one organism to another and among parts of the biosphere through closed loops (biogeochemical cycles), powered by the flow of energy.

Water cycle

Carbon cycle

Nitrogen Cycle

Phosphorus Cycle