---
title: "Quick check: keys and changing classification"
subtitle: "Year 7 Biology · Classification · Lesson 7"
---

# Quick check: keys and changing classification

**Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}}

> **Key question:** Can you build a key that a stranger could use? And why do the groups in the textbook keep changing?


:::teacher-note

**In one sentence:** A self-test on constructing dichotomous keys and on classification changing over time (AC9S7U01, nodes 4 and 5, both hinge nodes taught in class).

**Students should be able to say:** I can say what makes a good key question. I can say how many questions a key for six organisms needs. I can give an example of classification changing and the evidence behind it.

**Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet.

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## Building a key


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### Good key questions

**Would this make a good question in a key?**

Groups: Good question, Poor question

- Does it have six legs?: {{field-15}}
- Does it have feathers?: {{field-15}}
- Is it large?: {{field-15}}
- Is it scary?: {{field-15}}
- Does it have a shell?: {{field-15}}

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:::teacher-note

**Answer:** Does it have six legs? → Good question; Does it have feathers? → Good question; Is it large? → Poor question; Is it scary? → Poor question; Does it have a shell? → Good question

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:::keep-together

### How many questions?

**You build a key to identify 6 different organisms. About how many questions does it need?**

☐ 6: one per organism

☐ 12: two per organism

☐ 3: half the number of organisms

☐ 5: each question splits one group into two

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:::teacher-note

**Answer:** 5: each question splits one group into two

Each question splits one group into two, so to end with 6 separate organisms you make 5 splits.

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:::keep-together

### A peer tests your key

**A classmate follows your key and names a specimen wrongly. What does that tell you?**

☐ Keys cannot be made accurate

☐ Your key has a fault, such as an unclear question or a wrong branch, to find and fix

☐ The classmate is not good at science

☐ The specimen is not in the key

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:::teacher-note

**Answer:** Your key has a fault, such as an unclear question or a wrong branch, to find and fix

Testing with another person is the point: it shows up unclear questions you could not see yourself.

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:::keep-together

### A question that doesn't split

**A key ends with the question "Does it have four legs?" to separate a dog from a cat. What is wrong with it?**

☐ Both answers are yes, so the question doesn't split them: it needs a feature only one of them has

☐ Nothing: both animals reaching the same end is fine

☐ Legs are not an observable feature

☐ The key needs more animals in it

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:::teacher-note

**Answer:** Both answers are yes, so the question doesn't split them: it needs a feature only one of them has

Every question must split the group into two. Pick a feature one has and the other doesn't, such as "Does it have retractable claws?"

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## Classification changes


:::keep-together

### A reclassification

**Which is a real example of classification changing because of new evidence?**

☐ An animal changed its features during its life, so it was moved to a new group

☐ DNA comparisons showed that archaea are not bacteria, so a third domain of life was recognised

☐ A scientist preferred a different name, so the group was renamed

☐ Two groups looked alike, so they were merged without any new evidence

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:::teacher-note

**Answer:** DNA comparisons showed that archaea are not bacteria, so a third domain of life was recognised

Comparing DNA (and other molecules) showed archaea differ from bacteria as much as from us. Fungi were also moved: DNA shows they are closer relatives of animals than of plants.

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:::keep-together

### What can change it?

**Could this lead scientists to change a classification?**

Groups: Can change it, Cannot change it

- New DNA evidence: {{field-15}}
- A better microscope showing new structures: {{field-15}}
- A newly discovered species that does not fit: {{field-15}}
- An opinion with no evidence: {{field-15}}
- Wanting the groups to look neat: {{field-15}}

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:::teacher-note

**Answer:** New DNA evidence → Can change it; A better microscope showing new structures → Can change it; A newly discovered species that does not fit → Can change it; An opinion with no evidence → Cannot change it; Wanting the groups to look neat → Cannot change it

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:::keep-together

### Weaker or stronger?

**Scientists reclassified some organisms. Does that make science less trustworthy?**

☐ No: updating ideas when new evidence appears is how science works, and it makes the ideas more reliable

☐ It makes no difference to how reliable it is

☐ Yes: it shows scientists were wrong about everything

☐ Yes: classification should never change

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:::teacher-note

**Answer:** No: updating ideas when new evidence appears is how science works, and it makes the ideas more reliable

Science corrects itself. Because ideas are tested against new evidence, the ones that survive can be trusted more.

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## Exit ticket

:::keep-together

**Why must a key question be about something you can observe?**

{{lines-3}}

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:::teacher-note

**Answer:** So anyone can answer it the same way and reach the same organism.

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