Year 8 Science · Unit 1 · Lesson 7
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Learning Goals
Match each stage to what happens
Write the matching letter in the middle column. Each letter is used once.
| Stage | Letter | What happens |
|---|---|---|
| Uptake | A. Water moves up through the stem towards the leaves. | |
| Transport | B. Leaves droop because more water is lost than is taken up. | |
| Use | C. Water evaporates from the leaves into the air. | |
| Loss | D. Roots absorb water and dissolved minerals from the soil. | |
| Wilting | E. Leaf cells use water to make food and to stay firm. |
Classify and give a reason
Each observation is evidence for one stage: uptake, transport, use or loss. Write the stage, then the reason. Each stage is used once.
| Observation | Stage | Reason |
|---|---|---|
| 1. A clear plastic bag tied over a leafy branch fills with water droplets. | ||
| 2. Fine hairs on a seedling’s roots spread out through the damp soil. | ||
| 3. Leaves in sunlight make sugar, using water and carbon dioxide. | ||
| 4. A cut white carnation stood in blue-dyed water has blue-edged petals the next day. |
Cause and effect
A scientist blocks the water-carrying tubes in a geranium’s stem with wax. Complete the chain. Each box is caused by the box before it.
Investigation: celery in blue dye
A celery stalk is a leaf stalk: it carries water up to the leaves at its top, just as a stem does. Two fresh celery stalks of the same length were stood in the same blue dye, side by side in a sunny room. Stalk A kept its leaves. Stalk B had all its leaves cut off. Every 20 minutes a student measured how far up each stalk the blue colour could be seen.
| Time (min) | 0 | 20 | 40 | 60 |
|---|---|---|---|---|
| Stalk A (leaves on) | 0 | 3.1 | 6.0 | 9.0 |
| Stalk B (leaves removed) | 0 | 1.0 | 2.1 | 3.0 |
Source: sample class results.
1. How high had the dye travelled in each stalk after 40 minutes?
2. Calculate the average speed of the dye in each stalk over 60 minutes, in cm per minute. How many times faster was Stalk A?
Stalk A was times faster
3. Explain why the dye rose faster in the stalk with leaves. Use the idea of water loss from leaves.
4. In a test, Jay wrote: “Leaves do plant transport, because they are at the top.” Improve Jay’s answer so it shows how every part shares the work, and back it up with the celery results.
Match each stage to what happens
Uptake → D; Transport → A; Use → E; Loss → C; Wilting → B.
Classify and give a reason
1. Loss: water evaporated from the leaves and condensed on the bag. 2. Uptake: root hairs take in soil water. 3. Use: leaf cells use transported water. 4. Transport: dyed water was carried up the stem to the flower.
Cause and effect
Box 2: water taken in by the roots can no longer move up the stem to the leaves. Box 3: the leaves keep losing water to the air, but it is not replaced, so the leaf cells lose water and go soft.
Go Deeper
1. Stalk A: 6.0 cm. Stalk B: 2.1 cm. [2 marks]
2. Stalk A: 9.0 ÷ 60 = 0.15 cm per minute. Stalk B: 3.0 ÷ 60 = 0.05 cm per minute. 0.15 ÷ 0.05 = 3 times faster. [3 marks: 1 each speed, 1 comparison]
3. Leaves are where water is lost to the air. In Stalk A, water evaporating from the leaves was replaced by more water moving up the stalk, which carried the dye up quickly. Stalk B had no leaves, so very little water was lost from the top and the dyed water moved up much more slowly. [3 marks: leaves lose water; loss replaced from below; no leaves so slower]
Show What You Know
4. Marking guide: 1 for the claim (the statement is incomplete: leaves are only one part of a connected transport process, and being at the top is not the reason); 1 for roots (take in water and dissolved minerals); 1 for stem (connects roots to leaves and moves water up); 1 for leaves (use water and are where water is lost), supported by Table 1 (dye rose 3 times faster with leaves on); 1 for reasoning (uptake, transport and loss are linked, so removing any part slows or stops the whole process). Model answer: The idea is incomplete. Roots take in water and minerals, the stem carries water up, and leaves use some and lose some to the air. The celery dye moved three times faster with leaves on, because water lost from leaves is replaced from below. Leaves cannot do this without the roots and stem, so transport is one connected process. [5 marks]
Common error to watch for: thinking the stalk without leaves should move water faster “because it has less to fill”. Water moves faster when more is being lost at the top.