Food webs
A food web connects producers, consumers and decomposers. Producers bring in solar or chemical energy; feeding transfers some of it between organisms. Decomposers transform remains and release nutrients. A change in one population can indirectly affect others in the web.
Where this sits
- Comes after
- Energy & metabolism
Exercises from this rung
Generated by the app, from easiest to hardest
Put the food chain in order, from the one that starts with light to the last to eat.
Answer alga, snail, small fish, heron
Why alga → snail → small fish → heron. The arrow runs from the food to its eater, which is the path the energy takes. It always starts with something that photosynthesises, and it rarely goes beyond four or five links: at each one almost all the energy is lost along the way.
easierIn a sunlit pond, which organism can bring solar energy into the food web?
- A larva that eats algae
- A fish that eats insects
- A photosynthetic alga
Why Photosynthetic producers convert light energy into chemical energy in organic matter. Consumers obtain it by feeding. Producers that use chemical energy also exist, but in this pond the example is the alga.
in betweenIn an algae → snails → fish model, fish that eat snails increase. If other conditions stay the same, what indirect effect would you expect?
- Fewer snails and less grazing on algae
- No possible effect on algae
- More snails because they are fish food
Why More predation can reduce snails and ease grazing on algae: a trophic cascade. This is a model prediction, not a universal guarantee. In a real web, other foods, resources and behavioural responses can modify it.
harder