Year 8 Science · Unit 1 · Lesson 4
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Learning Goals
Match each part to its job
Write the matching letter in the middle column. Each letter is used once.
| Part | Letter | Job |
|---|---|---|
| Roots | A. The part of a leaf cell where light is used to make food. | |
| Stem | B. Flat parts that take in light and gases from the air and make food. | |
| Leaves | C. Makes seeds so the plant can reproduce. | |
| Cell wall | D. Hold the plant in the soil and take up water and minerals. | |
| Chloroplast | E. A stiff outer layer that supports a plant cell and gives it a fixed shape. | |
| Flower | F. Holds the plant upright and links the roots to the leaves. |
Odd one out
In each row, three items belong together and one does not. Circle the odd one out and give your reason.
| Row | Items | Reason |
|---|---|---|
| 1 | a bamboo cane · a parsnip · a tree trunk · a rose stem | |
| 2 | anchors the plant · absorbs water · takes in light · absorbs minerals | |
| 3 | a nucleus · a cell wall · a chloroplast · a large central vacuole |
Which part is harmed first?
For each event, name the part harmed first and its organ system (root or shoot). Then say how the rest of the plant is affected.
| Event | Part and organ system | Effect on the rest of the plant |
|---|---|---|
| Caterpillars eat most of a cabbage’s leaves. | ||
| A strong wind snaps a sunflower’s stem halfway up. | ||
| A new garden bed is dug and a shrub’s roots are cut. |
Scenario: a ringbarked tree
A farmer cuts away a strip of bark all the way round a tree’s trunk. Just under the bark is the tissue that carries food made in the leaves down to the roots. The leaves stay green for weeks, but months later the whole tree dies.
Cause and effect
Complete the chain. Each box is caused by the box before it.
Read the data
A class grew wheat seedlings in two trays of the same soil for four weeks. Tray 1 was watered every day; tray 2 once a week. They measured the longest root and the shoot height of five seedlings per tray and found the averages.
| Tray | Average root length (cm) | Average shoot height (cm) |
|---|---|---|
| 1: watered every day | 10 | 24 |
| 2: watered once a week | 18 | 15 |
Source: sample class results.
1. Which tray grew taller shoots?
2. How much longer were the roots in tray 2 than in tray 1, and how much shorter were the shoots?
Roots longer by cm
Shoots shorter by cm
3. Suggest why the seedlings watered only once a week grew longer roots but shorter shoots. Use the jobs of the roots and the leaves in your answer.
4. The class used only one tray for each watering plan. Suggest one change that would make the results more reliable.
Real-world context: grey mangroves
Grey mangroves (Avicennia marina) grow in the mud of NSW estuaries. The mud is waterlogged, so it holds very little oxygen, and it is salty. The roots send up pencil-like roots called pneumatophores, which poke above the mud and take in oxygen from the air. The leaves have salt glands that push out extra salt.
5. Explain how the grey mangrove survives as a living system in salty, waterlogged mud. Describe what its roots, stem and leaves each do, and explain how the pneumatophores and the salt glands help the rest of the plant stay alive.
Match each part to its job
Roots → D; Stem → F; Leaves → B; Cell wall → E; Chloroplast → A; Flower → C.
Odd one out
Row 1: a parsnip (a root; the rest are stems). Row 2: takes in light (a leaf job; the rest are root jobs). Row 3: a nucleus (in plant and animal cells; the rest only in plant cells).
Which part is harmed first?
Cabbage: leaves, shoot system; less food is made, so the whole plant grows slowly. Sunflower: stem, shoot system; the top is cut off from the roots, so its leaves get no water and wilt. Shrub: roots, root system; less water and fewer minerals are absorbed so the leaves wilt, and the shrub is less firmly anchored.
Cause and effect
Box 2: food made in the leaves can no longer travel down the stem to the roots. Box 3: the root cells run out of food, die and stop absorbing water.
Read the data
1. Tray 1 (watered every day), 24 cm. [1 mark] 2. Roots 18 − 10 = 8 cm longer; shoots 24 − 15 = 9 cm shorter. [2 marks]
3. With little water in the soil, longer roots can reach more of the water that is left, so more growth goes into the roots. Less water reaches the shoot, so the stem and leaves grow less. [3 marks: roots absorb water; less water for the shoot; the link]
4. Use several independent trays for each watering plan and average the tray results. [1 mark]
Show What You Know
5. Marking guide: 1 jobs of roots, stem and leaves; 1 root cells need oxygen that waterlogged mud cannot supply; 1 pneumatophores take in oxygen from the air for the roots; 1 salt glands remove extra salt so the leaves keep working; 2 for linking parts (roots keep absorbing only if they get oxygen; leaves need that water carried up the stem; roots need the leaves’ food). Model answer: Roots anchor and absorb water; the stem supports and links; leaves make food. Root cells need oxygen, but the mud has almost none, so the pneumatophores take it in from the air. The salt glands push out extra salt so the leaves can keep making food, and that food feeds the roots, so every part depends on the others. [6 marks]
Common error to watch for: listing the pneumatophores and salt glands without saying what each lets another part do.