Year 8 Science · Unit 1 · Lesson 4
Challenge Worksheet
Learning Goals
Find the errors
This paragraph contains exactly four errors. Underline each one and write the correction below.
A student’s summary
A plant is a living system because its parts are organised and work together. The roots anchor the plant and absorb water and minerals. The stem is only there to hold the plant up; nothing passes through it. Leaves take in light and use it to make food. The leaves keep all the food they make for themselves. Plant cells have a cell wall and chloroplasts. Animal cells also have a cell wall, but no chloroplasts. Because each part has its own job, the leaves could survive even if the roots were removed.
1. Write the four corrections.
Investigation: how firmly are seedlings anchored?
A class grew sunflower seedlings for one, two and three weeks. For each age they hooked a force meter under the seed leaves and pulled straight up until the seedling came out of the soil. They did three trials for each age and then washed the roots and measured them. In trial 2 for the three-week seedlings, the class recorded that the hook slipped at 1.1 N before the seedling came out of the soil.
| Age (weeks) | Average root length (cm) | Trial 1 (N) | Trial 2 (N) | Trial 3 (N) | Mean (N) |
|---|---|---|---|---|---|
| 1 | 3 | 0.4 | 0.5 | 0.3 | |
| 2 | 7 | 1.2 | 1.4 | 1.3 | 1.3 |
| 3 | 12 | 2.6 | 1.1 | 2.8 |
Source: sample class results.
2. Calculate the mean pulling force for the one-week seedlings.
Answer N
3. One result for the three-week seedlings came from a failed pull. Identify it, use the recorded problem to explain why it should be excluded, and calculate the mean for three weeks without it.
Mean without the anomaly N
4. A student concludes: “Longer roots make a seedling harder to pull out, so root length is the only thing that anchors a plant.” Evaluate this conclusion. Say what the data support and what they do not.
Test a gardener’s claim
A gardener claims
“If you cut most of the leaves off a young plant, its roots will grow bigger, because the plant no longer has to feed all those leaves.”
5. Before testing, predict whether the gardener is right. Justify your prediction using what roots need from the leaves.
Plan a short investigation
Plan a fair test of the question: Does removing leaves affect how much a bean seedling’s roots grow?
Hypothesis
If more leaves are removed, then the roots will …, because …
Variables
Method
What result would show the gardener is wrong?
6. “Leaves are the most important part of a plant, because they make the food.” Evaluate this statement, using evidence from this worksheet and what the other plant parts provide.
Find the errors
1. (i) The stem also connects the roots and leaves; water and food pass through it. (ii) The leaves share their food; it is carried to other parts, including the roots. (iii) Animal cells have no cell wall, only a cell membrane. (iv) The leaves could not survive without the roots, which supply their water and minerals. [4 marks: 1 per correction]
Your Turn
2. (0.4 + 0.5 + 0.3) ÷ 3 = 0.4 N. [2 marks] 3. Trial 2, 1.1 N. The recorded hook slip means the reading was not the force needed to pull the seedling out, so it should be excluded from this mean. A result should not be discarded just because it differs from the others. Mean: (2.6 + 2.8) ÷ 2 = 2.7 N. [3 marks: identify, recorded reason for exclusion, mean]
4. Supported: as root length rose from 3 to 12 cm, the force rose from 0.4 to about 2.7 N. Not supported: “the only thing”. Older seedlings also have more side roots and thicker stems, so length was not the only thing that changed; and only one plant, one soil and three trials per age were tested. [3 marks: trend; other variables; limited data]
Test a gardener’s claim
5. Probably wrong: roots cannot make food and get it from the leaves via the stem, so fewer leaves means less food and less root growth. [2 marks]
Investigation: Hypothesis: if more leaves are removed, the roots will grow less, because less food is made for them. Independent: number of leaves removed (none, half, all but one). Dependent: root length or mass after three weeks. Controlled: seedling type and age, soil, water, light. Method: three or more seedlings per group; remove leaves on day 1; grow side by side; measure roots; average. The gardener is wrong if seedlings with leaves removed have shorter or lighter roots.
Show What You Know
6. Marking guide: 1 position (partly right or wrong); 1 leaves make the plant’s food; 1 leaves need water and minerals from the roots; 1 the stem holds leaves to the light and links them to the roots; 1 evidence from this sheet; 1 judgement that each part depends on the others. Model answer: Only partly right. Leaves make food for the whole plant, but they need water and minerals from the roots, and the stem holds them to the light and links them to the roots. Roots also anchor the plant: the older seedlings with longer roots needed far more force to pull out. As a system, no single part is most important. [6 marks]
Common error to watch for: agreeing because leaves “do the most”.