Year 7 Science · Unit 1 · Lesson 1
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Learning Goals
Match each characteristic to an example
Write the letter of the matching example in the middle column. Each letter is used once. The examples are not in the same order as the characteristics.
| Characteristic | Letter | Example |
|---|---|---|
| Movement | A. A shark detects a tiny amount of blood in the water. | |
| Respiration | B. A female platypus lays two eggs. | |
| Sensitivity | C. A wombat’s kidneys remove the waste chemical urea, which leaves in its urine. | |
| Growth | D. A kangaroo hops across a paddock. | |
| Reproduction | E. A gum tree makes sugar in its leaves using sunlight. | |
| Excretion | F. Cells in a runner’s leg muscles release energy from food. | |
| Nutrition | G. A wattle seedling doubles in height by making more cells. |
1. What are all living things made of? About how wide is a typical one?
Order the organisms by number of cells
Number the organisms from 1 (fewest cells) to 4 (most cells).
| Order (1–4) | Organism |
|---|---|
| A blue whale | |
| A bacterium | |
| A human | |
| An ant |
2. Zara says: “A blue whale is more alive than a bacterium, because it has far more cells.” Explain why Zara is wrong.
3. A full stop printed on this page is about 0.5 mm wide. Most cells are about 0.01 mm across. How many cells would fit side by side across the full stop? Show your working.
Answer cells
Read the data: water bears
Scenario: tardigrades on the Moon
Tardigrades, or “water bears”, are tiny animals less than 1 mm long with eight stubby legs. They live in damp moss. When their home dries out, a tardigrade loses most of its water and curls into a dry ball called a tun. Dried tardigrades have survived extreme cold, strong radiation and even the vacuum of space. In April 2019 the Israeli spacecraft Beresheet crash-landed on the Moon carrying a small capsule of dried tardigrades.
| What was checked | Active tardigrade | Dried tun |
|---|---|---|
| Made of cells? | Yes | Yes |
| Moves | Walks through moss on eight legs | No movement |
| Feeds | Pierces algae and plant cells and sucks out the contents | Does not feed |
| Grows and lays eggs | Yes | No |
| Responds when touched | Pulls in its legs | No response |
| Respiration | Normal | So slow it can barely be measured |
| After a drop of water is added | Not tested | Swells up and starts walking and feeding within a few hours |
Source: simplified summary made for this worksheet.
4. Name four MRS GREN characteristics that an active tardigrade shows. For each one, quote the evidence from Table 1.
5. Which two rows of Table 1 are the best evidence that a tun is still alive, not dead? Explain your choice.
6. A news website reported: “Any tardigrades spilled on the Moon are dead, because they show none of the seven characteristics of life.” Evaluate this claim. Use MRS GREN, Table 1 and the difference between living, dead and non-living.
Match each characteristic to an example
Movement → D; Respiration → F; Sensitivity → A; Growth → G; Reproduction → B; Excretion → C; Nutrition → E.
Question 1
Cells (1); most are about 0.01 mm across, too small to see without a microscope (1). [2 marks]
Order the organisms by number of cells
Reading down the table as printed, the correct step numbers are 4, 1, 3, 2. In order: a bacterium (one cell); an ant (about a million cells); a human (about 37 trillion cells); a blue whale (roughly 100 quadrillion cells).
Question 2
A bacterium is living because it is made of cells and carries out the life processes; bacteria reproduce by cell division (1). Cell number tells you how big an organism is, not how alive it is (1). [2 marks]
Question 3
0.5 ÷ 0.01 (1) = 50 cells (1). [2 marks]
Read the data: water bears
4. Any four: movement (walks); nutrition (feeds on algae and plant cells); growth; reproduction (lays eggs); sensitivity (pulls in legs when touched); respiration (normal). 1 mark for two or three, 2 for four. [2 marks]
5. The respiration row (still happening, very slowly) and the “after a drop of water is added” row (swells up and starts walking and feeding again) (1). A dead thing could do neither: it would not respire at all and could not start moving and feeding again, so the tun’s life was only paused (1). Note: “made of cells” only shows it is not non-living; do not accept it as evidence that it is not dead. [2 marks]
Question 6
Marking guide: 1 judgement (not justified by that reason alone); 1 dead means once alive but never able to carry out the characteristics again, and a tun is made of cells so it cannot be non-living; 1 Table 1: a tun shows none of MRS GREN yet becomes active with water, so “none right now” does not prove death; 1 comparison with a dry seed (paused life); 1 no liquid water on the Moon, and the crash may have killed them; 1 the settling test: add water and see whether the tun resumes life activity; reproduction remains a species-level capacity. [6 marks]
Model answer: The claim is not justified. A tun shows none of the seven characteristics, but Table 1 shows a tun given water walks and feeds within hours, so its life can be paused, like a dry seed. It is made of cells, so it is not non-living; it is dead only if it can never carry out the characteristics again. The crash may have killed them and there is no water on the Moon to wake them, adding water can test whether they resume activity; the MRS GREN capacities are considered across an organism's life, and reproduction is at species level.
Common error: treating “shows no characteristics right now” as dead.