Energy Flow: Food Chains and Webs

1. Energy Flow: Food Chains and Webs

2. Energy Transfer • Energy transfers from one organism to another when they are consumed and metabolized. • Energy can be followed based on how organism obtain energy. • Trophic levels – the position of an organism in a sequence of energy transfer • Trophic levels are depicted in food chains.

3. Food Chains and Food Webs • A food chain is a single pathway of feeding relationships in an ecosystem • Draw the following food chain! • Feeding relationships are much more complex than a simple food chain. This complexity is shown through a food web. • Add on to the chain in a food web!

4. 10% rule • Every time energy is transferred from one organism to another, not all of the energy is passed on. In fact, more often than only a very low portion of the energy is transferred. • On average, only 10% of the total energy consumed in one trophic level is passed on to the next level. • Why?

5. Biomass • Because so little of the energy is transferred from trophic level to trophic level, the higher trophic levels can only support a limited number of organisms. • This is because they must consumer a greater number of organisms to reach the amount of energy they need to survive. • This is why an ecosystem will have less carnivores than herbivores. For example in Africa there about 1000 herbivores for every lion.

6. Biological Magnification • The low energy transfer in each trophic level can lead to some serious consequences in the higher trophic levels. • Biological magnification is the increase of a substance in food chains or webs due to the low transfer of energy which leads to the need for consumption of a greater number of organisms at the high trophic levels.

7. Food chains and webs • Create a food chain • Use 4 organisms and the sun • Use arrows in one color to show the flow of energy • Label each organism with its trophic level • Show how much energy is in each level • Label them with what type of producer or consumer they are (herbivore, carnivore, etc) • Make it a food web • Add 6 more organisms to your chain to make it a web • Use arrows in a second color to show the flow of energy • Label them with what type of producer or consumer they are (herbivore, carnivore, etc) • Explain the 10% rule and biological magnification in your own words on the back