Year 8 Science · Unit 1 · Lesson 6
Challenge Worksheet
Learning Goals
Evaluate the claim
Someone claims...
"Insects don't need hearts or lungs because they breathe through tiny tubes called tracheae that go directly to their tissues. This means insects can grow to any size they want, they just need more tracheae to supply the extra cells. Giant insects like the ones in old sci-fi movies could theoretically exist today if the conditions were right."
(a) What part of this claim is supported by the science you have learned? (Hint: think about how small organisms can rely on direct exchange.)
(b) What is misleading or scientifically incorrect about the claim that insects can grow to any size? Use the SA:V ratio concept in your answer. (Note: in the Carboniferous period, 300 million years ago, insects were much larger due to higher atmospheric oxygen, but even then, there were clear size limits.)
(c) What evidence or information would a scientist need to fully test whether a "giant insect" could survive? Suggest at least two pieces of evidence.
1. Giant wetas (Deinacrida sp.) are among the heaviest insects in the world, found in New Zealand. They are much larger than most insects, yet they still rely on a tracheal system with no heart or lungs. Explain why their large size, compared to most insects, suggests there is a biological size limit imposed by the tracheal system. Use SA:V ratio reasoning.
2. Compare how insects and mammals each solve the problem of supplying oxygen to their cells. What does this comparison tell us about the relationship between body size and transport system complexity?
Wrap Up
In one sentence, what was the main idea of this lesson?