Year 7 Science · Unit 1 · Lesson 9
Challenge Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. A red blood cell keeps its nucleus so that it can repair itself.
Correct it:
2. The midpiece of a sperm cell is packed with mitochondria, which release energy to power its tail.
Correct it:
3. A blood stem cell is unspecialised, so it can keep dividing and make new blood cells.
Correct it:
4. All the cells in your body have the same shape, because they all came from one original cell.
Correct it:
5. A neuron is long so that a signal has to be handed from cell to cell many times.
Correct it:
Find the errors
Sam’s revision table
| Row and cell | Job | Feature, and why it helps |
|---|---|---|
| 1. Red blood cell | Carries oxygen | A large nucleus controls how much oxygen the cell carries. |
| 2. Neuron | Carries electrical signals | A long axon, so one cell can carry a signal a long way. |
| 3. Root hair cell | Photosynthesis | Many chloroplasts to trap sunlight in the soil. |
| 4. Sperm cell | Swims to the egg and fertilises it | A flagellum (tail) that pushes it forward. |
| 5. Palisade cell | Photosynthesis | It sits on the shaded underside of the leaf, so it does not overheat. |
1. Three rows of Sam’s table contain a science error. For each wrong row, say what is wrong and write a correct version.
| Row | What is wrong, and the correct version |
|---|---|
2. Some deep-sea fish sense tiny movements (vibrations) in dark water. Design a specialised cell that could detect vibrations in water. Give three structural features and explain how each helps. You may adapt features you know from this lesson.
| Structural feature | How it helps the cell detect vibrations |
|---|---|
Read the data
Scenario: three model cells
A class made three model “cells” from modelling clay. Each model has the same volume, 1 cm³, but a different shape. They worked out the surface area of each one.
| Model | Size (cm) | Surface area (cm²) |
|---|---|---|
| Cube | 1 × 1 × 1 | 6.0 |
| Flat slab | 2 × 2 × 0.25 | 10.0 |
| Long thin rod | 16 × 0.25 × 0.25 | 16.1 |
Source: calculated values for made-up clay models.
3. How many times more surface area does the long thin rod have than the cube? Then describe the pattern in Table 1.
Answer times
4. Use the pattern to explain why a red blood cell is a flattened, dented disc rather than a ball. Then give one way the clay models are not like real cells.
5. A student says: “All cells are basically the same. They just have a nucleus and a membrane.” Evaluate this claim, using evidence from at least three specialised cells in this lesson.
True or false
1. False: a red blood cell pushes out its nucleus, so it cannot repair itself and lives about 120 days. 2. True. 3. True. 4. False: cells specialise, so their shapes differ to suit different jobs. 5. False: a neuron is long so that one cell can carry a signal a long way with no handover.
Find the errors
1. Row 1: a red blood cell has no nucleus, which leaves more room for haemoglobin to carry oxygen (1). Row 3: a root hair cell absorbs water and minerals, using a long thin extension that gives a large surface area; roots are in the dark and do not photosynthesise (1). Row 5: palisade cells sit in the sunlit upper layer of the leaf, to trap the most light (1). Rows 2 and 4 are correct. [3 marks]
Question 2
1 mark per feature with a reason that fits the job. For example: many fine hair-like extensions that bend when the water moves (a large area to catch movement); a long extension, like an axon, to carry the signal to the fish’s nerves without handover; many mitochondria to release energy for a cell that is always active. [3 marks]
Question 3
16.1 ÷ 6.0 ≈ 2.7 times (1). Pattern: for the same volume, the flatter or longer and thinner the shape, the larger the surface area (1). [2 marks]
Question 4
Like the slab, a flattened disc has more surface area than a ball of the same volume (1), so oxygen can enter and leave the cell faster (1). Limitation, for example: real cells are soft and curved, not rigid blocks, and have parts inside (1). [3 marks]
Question 5
Marking guide: 1 position (the claim is wrong or badly incomplete); 1 counter-example: a mature red blood cell has no nucleus; 3 one per cell with a feature linked to its job (for example neuron axon, sperm flagellum, palisade chloroplasts, root hair extension); 1 what it misses: in a many-celled body, cells specialise so structure fits function. [6 marks]
Model answer: The claim is wrong. A mature red blood cell has no nucleus at all, which leaves room for haemoglobin. A neuron has a very long axon to carry signals far, and a palisade cell is packed with chloroplasts for photosynthesis. Cells in a body are specialised, not the same.
Common error: listing cells and features without saying how each feature helps the job.