Question 39
Modelling DDT in a food chain
You will need:
- at least 25 people to do this activity – it’s even better with 30
- at least 200 tokens, some blue, some yellow, and some red
- a stopwatch
- a cup or small bag for each person, to put tokens in
- one card with ‘eagle’ written on it
- about eight cards with ‘small bird’ written on them
- about 21 cards with ‘insect’ written on them
- one bag, big enough to hold all the cards
- a method of marking out an area of ground outside, for example, traffic cones (you could borrow something from the sports department, or you might be able to use a marked-out part of a pitch used for sports)
- a clipboard and paper so that someone (the teacher, or the eagle) can record results
Method
1. Mark out an area big enough for people to run around. It could be 25 m by 25 m, but the exact size does not matter.
2. Spread all of the coloured tokens randomly in the marked-off area.
3. Put all of the cards into the large bag. Each person puts a hand into the bag and takes one card.
4. Everyone takes a small bag, and then stands on the edge of the marked-off area.
5. One person (it could be your teacher) starts a stopwatch and says: ‘Go!’ Each ‘insect’ goes and ‘feeds’ in the area. They do this by picking up tokens and putting them into their bags. Only one token can be picked up at once!
6. After 15 or 20 seconds, the timer shouts: ‘Stop!’ The insects stop feeding. Each ‘insect’ counts the tokens in their bag. They count how many tokens of each colour they have. The recorder writes down those results for each ‘insect’.
7. The timer starts the stopwatch again, and the ‘small birds’ go and feed on the ‘insects’. They do this by tapping an ‘insect’ on the shoulder. The captured insect transfers their tokens into the small bird’s bag. A ‘small bird’ can only eat one ‘insect’ at a time.
8. After 15 or 20 seconds, the timer shouts: ‘Stop!’ The ‘small birds’ stop feeding. The ‘insects’ (whether or not they have been eaten) move outside the marked area. Each small bird counts the tokens in their bag. The recorder writes down how many tokens of each colour each small bird has.
9. Now repeat steps 6 and 7, but this time the ‘eagle’ feeds on the ‘small birds’.
10. Go back into your classroom. The recorder can now write all of the results onto the board.
Editorial safety note: Work under teacher supervision in a clear area. Tap shoulders gently; do not push. Use tokens only, never real insecticide.
In this activity, you modelled what happens to DDT in a food chain. Do you think this is a good model of what happens in a real ecosystem? Explain your answer.
You will need:
- at least 25 people to do this activity – it’s even better with 30
- at least 200 tokens, some blue, some yellow, and some red
- a stopwatch
- a cup or small bag for each person, to put tokens in
- one card with ‘eagle’ written on it
- about eight cards with ‘small bird’ written on them
- about 21 cards with ‘insect’ written on them
- one bag, big enough to hold all the cards
- a method of marking out an area of ground outside, for example, traffic cones (you could borrow something from the sports department, or you might be able to use a marked-out part of a pitch used for sports)
- a clipboard and paper so that someone (the teacher, or the eagle) can record results
Method
1. Mark out an area big enough for people to run around. It could be 25 m by 25 m, but the exact size does not matter.
2. Spread all of the coloured tokens randomly in the marked-off area.
3. Put all of the cards into the large bag. Each person puts a hand into the bag and takes one card.
4. Everyone takes a small bag, and then stands on the edge of the marked-off area.
5. One person (it could be your teacher) starts a stopwatch and says: ‘Go!’ Each ‘insect’ goes and ‘feeds’ in the area. They do this by picking up tokens and putting them into their bags. Only one token can be picked up at once!
6. After 15 or 20 seconds, the timer shouts: ‘Stop!’ The insects stop feeding. Each ‘insect’ counts the tokens in their bag. They count how many tokens of each colour they have. The recorder writes down those results for each ‘insect’.
7. The timer starts the stopwatch again, and the ‘small birds’ go and feed on the ‘insects’. They do this by tapping an ‘insect’ on the shoulder. The captured insect transfers their tokens into the small bird’s bag. A ‘small bird’ can only eat one ‘insect’ at a time.
8. After 15 or 20 seconds, the timer shouts: ‘Stop!’ The ‘small birds’ stop feeding. The ‘insects’ (whether or not they have been eaten) move outside the marked area. Each small bird counts the tokens in their bag. The recorder writes down how many tokens of each colour each small bird has.
9. Now repeat steps 6 and 7, but this time the ‘eagle’ feeds on the ‘small birds’.
10. Go back into your classroom. The recorder can now write all of the results onto the board.
Editorial safety note: Work under teacher supervision in a clear area. Tap shoulders gently; do not push. Use tokens only, never real insecticide.
In this activity, you modelled what happens to DDT in a food chain. Do you think this is a good model of what happens in a real ecosystem? Explain your answer.
