1. V.C.E. Biology Unit 2 A Web of Interactions

2. Food Chains Food chains describe the feeding relationships within an ecosystem, showing who eats whom and the direction of energy flow (indicated by the arrow) Producers (autotrophs) – the important first link. These organisms trap light and chemical energy and convert it to simple sugars Consumers (heterotrophs) – they consume the producers or each other to receive the energy they need: Herbivores – eat only plant material Omnivores – eat plant and animal material Carnivores – eat only animal material

3. Food Chains Parasites – specialised consumers who live on and eat other consumers Scavengers – consumers that eat dead animals Detritivores – eat small particle of dead plant and animal material Decomposers – break down dead and decaying matter by secreting enzymes over them and absorbing the nutrients.

4. Food Webs Food webs display all the different feeding relationships within an ecosystem. Each of the organisms is ranked on a trophic level. Producers are level 1, herbivores are level 2, first order consumers feeding on the herbivores are level 3 etc. The food chains that make up a food web tend to have no more than 5 links, as the system is inefficient and there isn’t enough energy to sustain more than 5 trophic levels.

5. Food Webs

6. Competition Organisms tend to compete for available food, light, water, roosting sites, nesting sites, mates etc. Some organisms are more successful at competing with other organisms and are said to limit the distribution of the other species.

7. Interaction Symbiosis – is a term used to describe different species living in a close relationship. Mutualism – is a partnership between two different kinds of organisms that benefits both of the organisms. One example is the clown fish and the sea anemone.

8. Interaction Commensalism is a relationship whereby one organism benefits, but the other is neither harmed nor does it benefit. One example is that of epiphytic plants that use other plants for support.

9. Interactions Parasitism is when organism benefits, but the other is harmed in some way. One example is the aphid which suck sugar rich sap from the leaves and stems of plants.

10. Interactions Pollination – many plants need animals to help pollinate their flowers and mix up their pollen and ovules ensuring successful reproduction and variation of their gene pool.