Toxins in Food Chains and Organisms Changing Habitats · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How Toxins Build Up in Food Chains

Science · Ecosystems & Habitats · ages 12-13
Name ______________________   Date ____________

  1. Which of these is an example of an organism changing its own habitat?

    • A rabbit hopping across an open field
    • A beaver building a dam that turns a stream into a wetland
    • A bird flying south for the winter

  2. What does bioaccumulation mean?

    • A toxin building up inside a body faster than it can leave
    • A toxin spreading evenly through the whole food chain
    • A toxin breaking down into harmless parts over time

  3. True or false: top predators, like eagles and big fish, usually end up with the highest toxin levels in a food chain.

    Circle one:   True   False

  4. Why did DDT cause peregrine falcon populations to crash in the 1950s and 60s?

    • DDT built up in the falcons and made their eggshells too thin to survive
    • DDT made the falcons unable to see their prey
    • DDT killed off all the trees where falcons nested

  5. A small fish eats 100 contaminated insects. A big fish eats 20 of those small fish. Why does the big fish end up with more toxin in its body than any single small fish had?

    • Big fish bodies are naturally better at storing toxins
    • The toxin gets weaker each time it's eaten
    • It's collecting the toxin from all 20 small fish it ate

  6. In a pond, each small fish has stored 10 units of a toxin. A big fish eats 5 of those small fish and absorbs all their toxin. How many units of toxin does the big fish now have?

    Answer: ______________

  7. A beaver builds a dam and floods a valley into a wetland. How does this change end up affecting species other than the beaver?

    • It has no effect on any other species nearby
    • It dries out the area, forcing every other species to leave
    • It creates new habitat where fish, birds, and insects can move in

  8. Mia says plankton at the bottom of the food chain are in the most danger from a toxin, since they touch it first. Is she right?

    • Yes, because plankton are too small to survive any toxin
    • No, top predators are usually in more danger, since the toxin keeps adding up higher in the chain
    • Yes, because plankton cannot move away from the toxin
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Answer key

For grown-ups. Fold this page away before handing over the rest.

How Toxins Build Up in Food Chains W1-mt_YvCgDM0Scg-s1

  1. A beaver building a dam that turns a stream into a wetland · The beaver's dam reshapes the land itself, creating a new wetland habitat.
  2. A toxin building up inside a body faster than it can leave · Bioaccumulation is toxin building up inside a body over time because it comes in faster than it leaves.
  3. True · Top predators eat many already-contaminated animals, so the toxin keeps adding up in their bodies.
  4. DDT built up in the falcons and made their eggshells too thin to survive · DDT accumulated in falcons from the contaminated fish and birds they ate, thinning their eggshells until many eggs broke.
  5. It's collecting the toxin from all 20 small fish it ate · The big fish adds together the toxin from every small fish it eats, so its total keeps growing.
  6. 50 · 5 small fish times 10 units each equals 50 units now stored inside the big fish.
  7. It creates new habitat where fish, birds, and insects can move in · By reshaping the land, the beaver creates a new wetland habitat that many other species can use.
  8. No, top predators are usually in more danger, since the toxin keeps adding up higher in the chain · Each predator collects the toxin from many prey, so the amount grows biggest at the top of the chain, not the bottom.
Worksheet · LightMySky