Year 8 Science · Unit 1 · Lesson 18
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Learning Goals
Match each structure to its role
Write the matching letter in the middle column. Each letter is used once.
| Structure | Letter | Role |
|---|---|---|
| Xylem | A. Carries sugar made in the leaves to other parts of the plant. | |
| Phloem | B. Filter urea and extra water out of the blood. | |
| Stomata | C. Absorbs digested food into the blood. | |
| Alveoli | D. Carries water and minerals from the roots up to the leaves. | |
| Kidneys | E. Tiny pores that let carbon dioxide into a leaf, and oxygen and water vapour out. | |
| Small intestine | F. Tiny air sacs where oxygen passes into the blood and carbon dioxide passes out. |
Odd one out
Circle the odd one out in each row and say why it does not belong.
| Items | Odd one out, and why |
|---|---|
| 1. urea · carbon dioxide · oxygen · extra water | |
| 2. a muscle cell · the heart · the stomach · a kidney | |
| 3. carbon dioxide into a leaf · oxygen into the blood · carbon dioxide out of the blood · sugar into the phloem | |
| 4. a table of results · a confident opinion · a case study · a labelled diagram |
Scenario: wheat on salty soil
In some farming areas of Australia, salt has built up in the soil. Salty soil water makes it harder for roots to take in water. A farmer grew the same kind of wheat in four paddocks that all got the same rain, and the soil in every paddock was damp in spring. In the saltiest paddocks, many plants wilted in the middle of the day and the grain was small.
1. Name the three inputs a plant needs to survive and grow. Which one does salty soil stop the wheat getting enough of?
Cause and effect: from salty soil to a small harvest
Complete the chain. Each box is caused by the box before it. Name the plant structure involved in each box you write.
Read the data
| Paddock | Salt in the soil | Plants wilting at midday (%) | Grain harvested (tonnes per hectare) |
|---|---|---|---|
| North | high | 45 | 1.5 |
| Creek | very high | 80 | 0.6 |
| Hill | low | 5 | 3.0 |
| Dam | medium | 20 | 2.4 |
Source: sample paddock records.
2. The paddocks are not listed in order of salt. Describe the pattern in Table 1. Then calculate the percentage drop in grain harvested from the least salty paddock to the saltiest one.
Answer %
3. The farmer says: “The wheat in the salty paddocks is just short of rain. It would grow normally if it got more water.” Use the scenario and Table 1 to decide whether the evidence supports this claim. Give your reasoning.
4. A farm visitor says: “For a good harvest, only the heads of grain matter. The roots, stems and leaves are just there to hold the grain up.” Evaluate this claim. Work through the lesson’s problem-solving frame for at least three parts of the wheat plant, use evidence from Table 1, and finish with a clear judgement.
Match each structure to its role
Xylem → D; Phloem → A; Stomata → E; Alveoli → F; Kidneys → B; Small intestine → C.
Odd one out
1. oxygen (a useful input; the others are wastes the body removes). 2. a muscle cell (a cell; the others are organs). 3. sugar into the phloem (transport of food; the others are gas exchange). 4. a confident opinion (not evidence; the others are types of evidence).
Your Turn
1. Water, minerals and light. Salty soil stops the wheat getting enough water. [2 marks: 1 all three inputs, 1 water]
Chain, box 2: less water is carried up the xylem to the leaves, so the leaves wilt and the stomata close. Box 3: less carbon dioxide enters through the stomata, so the leaves make less sugar.
Read the data
2. The more salt in the soil, the more plants wilt and the less grain is harvested (low: 5%, 3.0 t; very high: 80%, 0.6 t). Drop: 3.0 − 0.6 = 2.4; 2.4 ÷ 3.0 × 100 = 80%. [3 marks: 1 pattern, 1 working, 1 answer]
3. Not supported. All four paddocks got the same rain and the soil was damp, yet wilting and harvest follow the amount of salt. The problem is that salty soil water is hard for the roots to take in, so more water in the soil would not fix it. The data did not test extra water, so this cannot be fully ruled out. [3 marks: 1 judgement, 1 evidence, 1 reasoning]
Show What You Know
4. Marking guide (points expected): 1 roots take in water and minerals; 1 xylem carries water up the stem to the leaves; 1 leaves take in carbon dioxide through stomata and make sugar; 1 phloem carries that sugar to the grain, so the grain depends on every other part; 1 evidence: where salt stopped the roots taking in water, 80% of plants wilted and the harvest fell from 3.0 to 0.6 tonnes per hectare, even though the heads were not damaged; 1 judgement: the claim is wrong; the plant is an organised system, and a problem in any part reduces the harvest. [6 marks]
Common error to watch for: in the chain and in Question 4, saying the roots or the soil give the grain its food. The sugar in the grain is made in the leaves and carried there in the phloem.