Year 8 Science · Unit 1 · Lesson 13
Challenge Worksheet
Learning Goals
Find the errors
This paragraph has exactly three errors. Underline each one and correct it below.
A student’s revision notes
Plants need three key inputs: water, minerals and light. Roots take in water and minerals from the soil, but their main job is really just to anchor the plant. Leaves are linked to light and to gas exchange: they take in oxygen to make food and let carbon dioxide out. Minerals are the plant’s food, which is why fertiliser is sold as “plant food”.
1. Write the three corrections.
Investigation: a lettuce trial in a school garden
Students grew 12 lettuces of the same variety, 4 in each of three garden beds, for 8 weeks. All beds were watered the same. Bed 1 got full sun and fertiliser. Bed 2 got full sun but no fertiliser. Bed 3 got fertiliser but sat under shade cloth that blocks half of the light. The students weighed each lettuce at harvest.
| Bed | Lettuce 1 | Lettuce 2 | Lettuce 3 | Lettuce 4 | Mean |
|---|---|---|---|---|---|
| 1: sun and fertiliser | 210 | 190 | 205 | 195 | 200 |
| 2: sun, no fertiliser | 130 | 118 | 126 | 126 | |
| 3: fertiliser, half shade | 150 | 144 | 160 | 146 | 150 |
Source: sample class results.
2. (a) Calculate the mean mass for bed 2 and write it in the table. (b) Calculate the percentage decrease in mean mass from bed 1 to bed 2, and from bed 1 to bed 3.
(b) Bed 2 % Bed 3 %
3. A student concludes: “Minerals are more important than light for all plants.” Use the trial to say what the data does show, then give two reasons why this conclusion goes too far.
Evaluate the claim
An office worker claims
“My desk plant sits by a big sunny window, so it has everything it needs. I never water it or add anything to the pot. Light is all a plant needs.”
4. Identify the part of the claim that is correct. Then name the inputs the plant is missing, the structure linked to them, and predict what will happen to the plant over the next few weeks.
5. Plan a test of this question: Do radish seedlings need minerals to grow well? You have 20 radish seedlings, pots of washed sand (no minerals), pure water, a mineral mix to dissolve in water, a sunny windowsill and a ruler.
Prediction, with a reason
Variables
Why use 10 seedlings in each group instead of 1?
6. A student says: “Animals are living systems because they eat, breathe and move materials around. Plants just sit in the sun, so they are not really living systems.” Evaluate this claim.
Find the errors
1. (i) Roots are not just anchors: taking in water and minerals is a main job. (ii) Leaves take in carbon dioxide to make food and let oxygen out. (iii) Minerals are not food: the plant makes its own food in its leaves using light; minerals are a separate input. [3 marks: 1 per correction]
Your Turn
2. (a) (130 + 118 + 126 + 126) ÷ 4 = 500 ÷ 4 = 125 g. (b) Bed 2: (200 − 125) ÷ 200 × 100 = 37.5%. Bed 3: (200 − 150) ÷ 200 × 100 = 25%. [4 marks: 1 mean; 1 method (drop ÷ bed 1 mean × 100); 1 per correct percentage]
3. Shows: here, no fertiliser cut mass more (37.5%) than half shade (25%); both inputs mattered. Too far, any two: one kind of plant only; one garden and season; light was halved, not removed, so the two changes are not equal; only 4 plants per bed. [3 marks: 1 what it shows; 1 per reason, up to 2]
Evaluate the claim
4. Correct: light is a key input, captured by the leaves. Missing: water and minerals, taken in by the roots. Prediction: the soil dries out, the plant wilts, then dies. [4 marks: correct part; missing inputs; roots; prediction]
5. Prediction: seedlings given minerals grow taller and greener, because minerals are needed for healthy growth. Independent: mineral mix or pure water. Dependent: height after a set time. Controlled (any two): volume of water, sand, light, time, starting size. Ten each: one seedling may be unusual; a mean of 10 is more reliable. [5 marks: prediction with reason; independent; dependent; two controlled; repeats]
Show What You Know
6. Marking guide (points expected): 1 correct parts (animals do take in materials; plants do need light); 1 plants also need water and minerals; 1 roots take in water and minerals, leaves capture light and exchange gases; 1 a missing input stops healthy growth or survival (no water: it wilts and dies); 1 both rely on organised structures for intake, but inputs and structures differ; 1 judgement: the claim is wrong; plants are living systems too. [6 marks]
Common error to watch for: in Q2 (b), dividing the drop by the smaller mean (75 ÷ 125) instead of by the starting mean from bed 1.