Year 7 Science · Unit 1 · Lesson 2
Challenge Worksheet
Learning Goals
1. Classification helps scientists in four ways. Name all four.
2. In the 1970s Carl Woese studied bacteria. What did he look at, and what did he discover?
3. Imagine scientists find a new animal in a Queensland rainforest. It has fur, and the female feeds her young on milk. Name the class it belongs to, and predict two other features it will have before anyone checks. Then explain why it matters that a prediction like this could turn out to be wrong.
Kingdom and domain
Complete the table. Every organism needs both a kingdom and a domain.
| Organism | Kingdom | Domain |
|---|---|---|
| A single cell with a nucleus that swims in pond water | ||
| A single cell with no nucleus from a very salty lake, whose DNA is very different from bacteria | ||
| A river red gum | ||
| Bread mould |
4. A friend is told only the domain of the bread mould. Explain why this tells them less about the mould than its kingdom would.
Check the scientific names
A student wrote these names by hand and underlined each one. Tick the names that are written correctly. Rewrite the others correctly.
| Name as written | Correct? (✓ or ✗) | Correct version, if needed |
|---|---|---|
| Homo Sapiens (human) | ||
| Eucalyptus camaldulensis (river red gum) | ||
| rufus Osphranter (red kangaroo) | ||
| TELOPEA SPECIOSISSIMA (waratah) | ||
| atrax robustus (Sydney funnel-web spider) |
Read the data: comparing DNA
Scenario: four look-alike microbes
Four single-celled microbes, all with no nucleus, look almost the same under a microscope. They come from garden soil, yoghurt, a deep-sea vent and a very salty lake. A scientist compares the code of one gene in each microbe, and in yeast, which has a nucleus. Table 1 shows how much of the code is the same for each pair.
| Pair compared | Code that is the same (%) |
|---|---|
| Soil microbe and yoghurt microbe | 88 |
| Soil microbe and vent microbe | 62 |
| Vent microbe and salty-lake microbe | 86 |
| Yoghurt microbe and salty-lake microbe | 60 |
| Soil microbe and yeast | 58 |
| Vent microbe and yeast | 64 |
Source: made-up numbers that show the kind of pattern DNA studies found.
5. Use Table 1 to sort the four microbes into two groups. Name the domain each group belongs to, and quote the numbers that support your grouping.
6. Under a microscope the four look almost identical. Why were they once grouped together, and what does the gene code reveal that looking could not?
7. A student argues: “The 5-kingdom system is enough. We don’t need domains.” Evaluate this claim. Use Archaea, Table 1 and what the lesson says about predictions that fail.
Question 1
Organise, identify, predict, communicate. [2 marks: 1 for two or three, 2 for all four]
Question 2
He looked at the DNA of bacteria (1) and found that not all “bacteria” are closely related: some are very different at the genetic level, which led to the three domains (1). [2 marks]
Question 3
Class Mammalia (1). Two predictions: it is warm-blooded, and it breathes with lungs (1 each). A prediction that could fail can be tested; if enough predictions fail for a group, the group was wrong and must be redrawn, which is what makes classification science and not just tidying (1). [4 marks]
Kingdom and domain
Pond cell: Protista, Eukarya. Salty-lake cell: Monera, Archaea. River red gum: Plantae, Eukarya. Bread mould: Fungi, Eukarya. [4 marks: 1 per row, both cells correct]
Question 4
Eukarya holds four kingdoms, including animals, plants and protists, so it only says the mould’s cells have a nucleus (1). The kingdom Fungi is a smaller group, so it also says the mould cannot make its own food, absorbs nutrients and has chitin cell walls (1). [2 marks]
Check the scientific names
Homo Sapiens: ✗, Homo sapiens (species all lowercase). Eucalyptus camaldulensis: ✓. rufus Osphranter: ✗, Osphranter rufus (genus first). TELOPEA SPECIOSISSIMA: ✗, Telopea speciosissima (only the genus has a capital). atrax robustus: ✗, Atrax robustus (genus needs a capital). Every rewrite is underlined. [5 marks: 1 per row]
Read the data: comparing DNA
5. Group 1: soil and yoghurt microbes, 88% the same (1), Domain Bacteria. Group 2: vent and salty-lake microbes, 86% the same, Domain Archaea (1). Pairs across the groups share only 60–62% (1). [3 marks]
6. Under a microscope all four are single cells with no nucleus, so they look alike and were grouped together (1). The DNA shows two groups that are very different from each other (1): the vent microbe shares about as little code with the soil bacterium (62%) as it does with yeast (64%) (1). [3 marks]
Question 7
Marking guide: 1 clear judgement (the claim is only partly right: kingdoms work well for most school biology and are easy to use, but they miss an important difference); 1 Archaea are single cells with no nucleus, with very different chemistry from bacteria, found in extreme places such as hot springs, deep-sea vents and very salty lakes; 1 Table 1 evidence (for example 86% and 88% within groups against 60–62% between them); 1 the 3-domain system splits Monera into Bacteria and Archaea and puts the other four kingdoms in Eukarya; 1 domains sit above kingdoms, so the two systems work together; 1 Monera failed as a group, because members did not share the features the group predicted, so it had to be redrawn. [6 marks]
Model answer: The claim is only partly right. The five kingdoms are easy to use and work for most organisms, but Kingdom Monera hides a big difference. Archaea look like bacteria, single cells with no nucleus, but their chemistry is very different and many live in extreme places such as deep-sea vents and salty lakes. In Table 1 the two bacteria share 88% of the gene’s code and the two Archaea 86%, but a bacterium and an archaeon share only 60–62%. Monera was a grouping whose predictions failed, so it was redrawn. The 3-domain system places Bacteria and Archaea in separate domains and puts every organism with a nucleus in Eukarya. Domains sit above kingdoms, so we still use kingdoms, but we do need domains.
Common error: grouping microbes by how they look under a microscope. Two microbes can look alike and still be very different in their DNA.