Year 7 Science · Unit 1 · Lesson 7
Challenge Worksheet
Learning Goals
1. Name the three parts found in plant cells but not in animal cells, and give the job of each.
Find the errors
A student wrote these revision notes. Three of the five lines contain one error each. For each line write “correct” or rewrite the error so the line is true.
| Student’s note | Correct, or your correction |
|---|---|
| 1. Cell wall: a thin, flexible layer that controls what enters and leaves the cell. | |
| 2. Nucleus: the control centre of the cell; it stores the DNA. | |
| 3. Chloroplasts: found in every plant cell, where they use sunlight to make glucose. | |
| 4. Mitochondria: only in animal cells, because plant cells get their energy from chloroplasts. | |
| 5. Large vacuole: stores water; when full, it presses out on the cell wall and keeps the cell firm. |
Read the data
Scenario: which plant parts can catch light?
A science club tested five parts taken from vegetables and garden plants: spinach, a bean stem, a carrot, an onion and a branch. For each part they tallied 50 cells and noted how many held any chloroplasts at all.
| Plant part | Where it grows | Cells with chloroplasts (out of 50) |
|---|---|---|
| Spinach leaf | In full sun | 48 |
| Skin of a green bean stem | In the light | 31 |
| Carrot root | Underground | 0 |
| Onion bulb skin (inner layer) | Underground | 0 |
| Wood from the middle of a branch | Inside the branch, in the dark | 0 |
Source: made-up tallies for this worksheet.
2. Which of the five places can carry out photosynthesis? Explain how Table 1 tells you.
3. Before looking, one student predicted that leaf cells would contain chloroplasts far more often than root cells. Evaluate this prediction using Table 1, and explain why the numbers differ. Link your answer to the job of chloroplasts and the conditions each cell lives in.
4. A classmate says: “The carrot, onion and wood cells have no chloroplasts, so they can’t be plant cells.” Is the classmate right? Give a reason from the lesson.
Plan a short investigation
Question: “Does the amount of light a plant receives affect the number of chloroplasts in its leaf cells?” You have six young bean plants, a sunny windowsill, a shady corner and a light microscope.
Hypothesis
If a plant gets more light, then its leaf cells will …, because …
Variables
Method
One limitation, and how to reduce it
5. Mushroom cells have cell walls too, made of chitin rather than cellulose. Use this to explain why “it has a cell wall” does not prove a cell is a plant cell. What does a cell wall rule out?
6. A sunflower droops on a hot, dry afternoon. A jarrah fence post never droops, even in a drought. A student says: “They are both held up in exactly the same way.” Evaluate this claim using what you know about cell walls and vacuoles.
Question 1
Cell wall: cellulose layer that keeps the cell rigid (1). Chloroplasts: use sunlight to make glucose (1). Large vacuole: stores water, keeps the cell firm (1). [3 marks]
Find the errors
1. Error: that is the membrane; the wall is rigid cellulose that holds the shape. 2. Correct. 3. Error: only cells that get light have chloroplasts. 4. Error: plant cells have mitochondria too. 5. Correct. [3 marks: 1 per corrected error]
Question 2
Spinach leaf and bean stem skin (1): only they have chloroplasts (1). [2 marks]
Question 3
Supported: 48 of 50 leaf cells, 0 of 50 carrot cells (1). Chloroplasts need light to make glucose (1). Roots are in the dark, so the plant does not build them there (1). [3 marks]
Question 4
No (1). They have cellulose cell walls; a plant only puts chloroplasts in cells that meet the light (1). [2 marks]
Plan a short investigation
Hypothesis with a reason (1). Independent: light (window or shade) (1). Dependent: average chloroplasts per leaf cell (1). Controlled, any two: plant type, age, water, soil, leaf sampled (1). Method: three plants per place, same time, same leaf position, same number of cells, average (1). Limitation and fix, for example count more cells (1). [6 marks]
Question 5
Fungi (and bacteria) have walls too, so a wall does not prove a plant (1). It does rule out an animal cell (1). [2 marks]
Question 6
Marking guide: 1 position; 1 both rely on cellulose walls; 1 sunflower cells turgid from full vacuoles; 1 dry day, vacuoles empty, droops; 1 wood cells dead, no vacuoles, thick glued walls; 1 so no water pressure needed. [6 marks]
Model answer: Only partly true. Both rely on cellulose walls. In the sunflower, full vacuoles push on walls, so cells are firm; when they lose water, it droops. Jarrah cells are dead, with no vacuoles; their thick, glued walls stay stiff without water.
Common error: saying a wilted plant has weakened cell walls. The walls are unchanged; the water pressure is gone.