1. Food Webs and Ecological
Pyramids
8SCIENCE Tues., Nov. 9

2. Review: what is a food web?
• Food chains and
food webs show
how organisms
get energy from
their food
• Food webs show
interconnected
or overlapping
food chains

3. Ecological
pyramids
• Shows how energy is
transferred from one
organism to another
• Pyramid bottom shows
the producers
• Pyramid top shows
the top carnivores or
top predators

4. How much energy is passed from one
organism to another?
• Remember: most food chains
only have 3 – 4 links or levels
– Why?
• At each level energy is lost
because organisms need to
use their energy from food to
perform their daily activities:
– look for more food
– find mates
– create a shelter
• When an organism eats
another organism for
energy, it is only
receiving about:
– 10% of the available energy

5. Bioaccumulation
• When an organism eats another organism, it gets
energy from what that organism ate as well
– Example: if a wolf is eating a rabbit for energy, it is
also eating the grass that the rabbit ate for energy
• If the food the organism eats is contaminated
with chemicals (like a pesticide), this can affect
the top carnivores or predators
• As one organism eats another the toxic chemicals
also move UP the food chain
– Example: Mercury poisoning from fish, humans can
become sick

6. Deadly Links Game
• The purpose of this game is to understand the relationships in
the food chain, and how these can lead to bioaccumulation of
substances
• Instructions:
– You will be assigned to be a hawk, shrew or grasshopper
• Blue = grasshopper
• Black = shrew
– If you are a grasshopper you will be given a stomach (clear
plastic bag)
– When I say go, the grasshoppers may walk around and
collect as much food as you can – you will have 30 seconds

7. Deadly Links Instructions continued…
• After 30 seconds the shrews will be released into the area and
they may catch the grasshoppers for food
– If you are caught: You MUST give the shrew your energy
(food) by giving them your ‘stomach’ (clear plastic bag)
– The shrews will continue to collect food for another 30
seconds
• Lastly, the hawks will be released and try to catch the shrews
for energy while the shrews continue to try and catch the
grasshoppers
• After 30 seconds, I will ask you to return to your seat with the
food that you have been able to ‘catch’ and sit quietly, wait for
the next instructions

8. Deadly Links instructions continued….
• Count the amount of food/energy you have
caught
• Does anyone have any white beans?
– If you have over 10 white beans you have the
lethal amount of pesticide called DDT
– This means you have died from DDT poisoning! 
• How many organisms are still alive?
• What type of organisms are still alive?

9. Deadly Links questions:
• Please answer these questions on a separate piece of paper and hand
them in for the end of class: EACH person must answer their own
questions for a grade out of
1) Draw the food chain that we acted out in the deadly links game. Use the
names of the animals and don’t forget about your arrows! (4)
2) Why do you think there were more grasshoppers than shrews at the
beginning? (1)
3) Why did the shrew take the grasshopper’s bag when he/she was tagged?
(1)
4) Why was the number of hawks the same at the beginning and at the end?
(1)
5) Describe what happened when the white/yellow beans actually turned out
to be poison for the animals. (3)