Year 8 Science · Unit 1 · Lesson 2
Challenge Worksheet
Learning Goals
Spot and fix three errors
This paragraph contains exactly three errors. Underline each one and write the correction below.
A student’s notes
Epithelial tissue is made of long fibres that contract to move the body. Nervous tissue carries signals around the body. A tissue is a group of similar cells working together. The heart is an organ because it is very large. Inside each cell, the ribosomes control all of the cell’s activities.
1. Write the three corrections.
2. The inside of your cheek is lined with epithelial tissue: thin, flat cells packed tightly together in a sheet. Explain how this structure suits its function of covering and protecting the surface.
Stubbing your toe
When you stub your toe, you usually feel the bump straight away and then, a moment later, a deep ache. Two kinds of nerve cell carry these messages from the toe to the spinal cord, which is about 1 m away in a tall teenager. Each of these nerve cells is one single cell that stretches almost the whole distance.
| Kind of nerve cell | Message it carries | Typical signal speed (m/s) |
|---|---|---|
| Fast nerve cell | touch and pressure (the bump) | 50 |
| Slow nerve cell | dull, aching pain | 1 |
Source: typical figures for these two kinds of nerve cell.
3. Calculate how long the touch message takes to travel 1 m from the toe to the spinal cord. Use time = distance ÷ speed.
Answer s
4. How many times longer does the aching-pain message take than the touch message? Show both times.
Answer times
5. Use the stimulus and your answers to explain why a nerve cell is a good example of a specialised cell. Link one feature of its structure to its function.
Plan an investigation
A question from the garden
A gardener notices that leaves on the sunny side of a lilly pilly hedge feel thicker than leaves on the shady side. Inside a leaf, the palisade tissue is the layer of tall cells that captures most of the light used to make food. She wonders whether sun leaves have a thicker palisade layer than shade leaves.
Hypothesis
If a leaf grows in ..., then its palisade layer will be ..., because ...
Variables
Method
6. Her first plan is to measure one sunny leaf and one shady leaf. Explain why this would not give a reliable answer, and state what she should do instead.
7. A student says: “Muscle is a tissue. That is all it ever is.” Evaluate this claim. Use a single muscle cell, muscle tissue and a whole muscle such as the biceps in your arm (which also contains connective tissue, nerve tissue and blood vessels). Finish with a judgement about when the claim is right and when it is wrong.
Spot and fix three errors
1. (i) Contracting fibres are muscle tissue; epithelial tissue lines and covers surfaces. (ii) The heart is an organ because it has different tissues working together, not because of size. (iii) The nucleus controls the cell; ribosomes make proteins. [3 marks: 1 per correction]
Your Turn
2. The cells are packed tightly with no gaps, so germs and harmful substances cannot get between them, and the flat cells form one continuous covering sheet. [2 marks: 1 structure, 1 link to barrier function]
3. time = 1 ÷ 50 = 0.02 s. [2 marks: 1 working, 1 answer with unit]
4. Pain: 1 ÷ 1 = 1 s. Touch: 0.02 s. 1 ÷ 0.02 = 50 times longer. [2 marks: 1 both times, 1 answer]
5. Its long, thin extension lets one cell reach almost from the toe to the spinal cord, which suits carrying messages quickly over a long distance (touch arrives in 0.02 s). [2 marks: 1 structure, 1 function]
Plan an investigation
Hypothesis: If a leaf grows in sun, its palisade layer will be thicker, because there is more light for its cells to use in making food. Independent: sunny side or shady side of the hedge. Dependent: thickness of the palisade layer (in µm, measured under a microscope). Controlled (any two): same hedge; leaves of the same age and height; same day; same slicing method; same microscope and magnification. Method: 1. Pick at least five grown leaves from each side at the same height. 2. Cut a thin slice across the middle of each. 3. Measure the palisade layer under the microscope with the scale. 4. Record in a table and average each side. [Hypothesis 2, variables 3, method 3]
6. One leaf could be unusual (young, damaged or naturally thin), so a difference might be chance, not light. She should measure at least five leaves from each side and compare averages. [2 marks]
Show What You Know
7. Marking guide: 1 what is correct (muscle tissue is many similar muscle cells working together); 1 muscle cell = cell (one specialised unit); 1 muscle tissue = tissue; 1 biceps = organ (muscle, connective and nerve tissue working together to move the arm); 1 “muscle” can name different levels; 1 justified judgement (right for muscle tissue, wrong for a whole muscle, which is an organ). [6 marks]
Common error to watch for: in Q4, answering “0.02 times”. The longer time goes on top: 1 ÷ 0.02 = 50.