Year 7 Science · Unit 1 · Lesson 15
Challenge Worksheet
Learning Goals
Evaluate the claim
Read the claim below carefully. Answer all three questions using scientific ideas from this lesson.
Someone claims...
"Mutualism is the ideal relationship in nature — all organisms should benefit from interacting with each other. Parasitism is 'cheating' and is a sign that ecosystems are out of balance. If we eliminated all parasites from the planet, ecosystems would be healthier and biodiversity would increase."
(a) What part of this claim is supported by the science you have learned? Explain what is correct.
(b) What is misleading or missing from this claim? Consider what role parasites actually play in ecosystems, and what "eliminating all parasites" might actually do to food webs and population control.
(c) What evidence or extra information would you need to decide whether this claim is reliable? Give at least two specific types of evidence a scientist would look for.
1. Classify each of the following three real-world relationships as mutualism, commensalism, or parasitism. For each one, state the effect on each organism using the +/− notation (e.g. ++ or +0 or +−) and justify your classification in one sentence.
| Relationship | Classification | Effect (+/−) | Justification |
|---|---|---|---|
| Mistletoe grows on a eucalyptus tree, taking water and nutrients from the tree's tissue. | |||
| An oxpecker bird perches on a rhinoceros, eating ticks and parasites from its skin. | |||
| A remora fish attaches to a shark's underside and feeds on scraps from the shark's meals, while the shark neither gains nor loses. |
2. A conservation scientist argues that removing introduced European rabbits from an Australian national park will benefit native marsupials. Using what you know about interspecific competition and carrying capacity, explain why the scientist's prediction is likely to be correct. Include both scientific terms in your answer.
Wrap Up
In one sentence, what was the main idea of this lesson?