Year 7 Science · Unit 1 · Lesson 02
Challenge Worksheet
Learning Goals
Design a mini-experiment
A scientist wants to test: "Does the 3-domain system or the 5-kingdom system more accurately reflect the evolutionary relationships between living things?" Plan the investigation below. Hint: think about what type of evidence — DNA sequences or physical cell features — you would compare, and how you would decide which system "fits" the data better.
| What I will change (independent variable) Which classification system am I comparing? |
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| What I will keep the same (controlled variables — list 3) What must stay constant to make this a fair test? |
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| What I will measure (dependent variable) What evidence will I collect? (e.g. DNA similarity %, presence of nucleus, membrane chemistry) |
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| My prediction Which system do you think will fit better, and why? |
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| How I would know if my prediction is wrong What result would force you to change your mind? |
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| One limitation of this investigation What makes this hard to test fairly? (e.g. cost of DNA sequencing, number of species you could include) |
1. In Australia, the red-bellied black snake (Pseudechis porphyriacus) is called "red-belly" in NSW, "red-bellied blacksnake" in Victoria, and "red snake" in some rural areas. In parts of South-East Asia, an unrelated snake with a red belly also has a local name that translates to "red-belly snake." Explain why binomial naming matters in this situation, and what problems could arise if scientists relied only on common names. Use specific examples in your answer.
2. Carl Woese proposed the 3-domain system in the 1970s after comparing the ribosomal RNA (a type of genetic molecule) of thousands of organisms. He found that Archaea, although they look like bacteria under a microscope, are genetically as different from bacteria as they are from humans. Evaluate the claim: "The 5-kingdom system is good enough — scientists don't need the 3-domain system." In your answer, explain what evidence supports the 3-domain system and what limitation the 5-kingdom system has.
Wrap Up
In one sentence, what was the main idea of this lesson?