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Primary Science · Year 3Chapter 3 · What plants need
Year 3 Science · What plants need · Lesson 3.5

Year 3 Science: How water travels up the plant

Part of the Year 3 Science what plants need chapter. Chapter overview · whole chapter on one page

3.5

How water travels up the plant

Year 3
Investigate the way in which water is transported within plants: from the roots, up the stem, to the leaves
Story. Kofi puts a celery stick in a glass of water with blue food colouring. Priya asks, “How will the blue get up to the leaves?” Kofi says, “Maybe the water climbs up through the middle of the stick.”

The roots take in water from the soil. The water then travels up through the stem to the leaves and flowers. It moves through tiny tubes inside the roots, the stem and the leaves. The scientific name for these tubes is xylem.

Moving something from one place to another is called transport. So this is called water transport: the water is carried up the plant to the places where it is needed.

Some water leaves the plant through tiny holes in the leaves, as water vapour. This loss of water helps to pull more water up the stem from the roots.

water vapourwater moves uptiny tubesroots
Water goes up from the roots, through tiny tubes in the stem, to the leaves. Some water leaves the leaves as vapour.

Key ideas

  • Water travels up the plant through tiny tubes, called xylem.
  • Water starts in the roots and travels up the stem to the leaves.
  • Water leaves the leaves as water vapour.
  • Transport means moving something from one place to another.
Worked example 3.5.1
Kofi measures the coloured line on the celery stick. Use the table. How far up the stick has the coloured water moved after 1 hour?
TimeHeight of coloured line
after 1 hour3 cm
after 3 hours9 cm
after 5 hours17 cm

Method. Find the row for 1 hour, and read the height.

  1. Find the row. The first row is for after 1 hour.
    first row
  2. Read the height. The coloured line is at 3 cm after 1 hour.
    3 cm
  3. Check the start. The coloured water started at the bottom of the stick, at 0 cm.
    started at 0
  4. Write the answer.
    3 cm

Check. The coloured line rose 3 cm from 0 cm. ✓

Worked example 3.5.2
Use the same table. How far did the coloured water rise between 3 hours and 5 hours?

Method. Take the height at 3 hours away from the height at 5 hours.

  1. Read the two heights. The line was at 9 cm after 3 hours and at 17 cm after 5 hours.
    9 and 17
  2. Find the rise. The rise is the bigger height minus the smaller height.
    17 − 9 = 8
  3. Write the answer.
    8 cm

Check. 9 + 8 = 17, so the answer is right. ✓

Worked example 3.5.3
Put these in the order that water travels from the soil: leaves, soil, stem, roots. Write the order.

Method. Start in the soil, and follow the water to the leaves.

  1. Start in the soil. The water starts in the soil.
    soil first
  2. Go to the roots. The roots take in the water from the soil.
    roots next
  3. Go up the stem. The water travels up the stem, and reaches the leaves last.
    stem then leaves
  4. Write the answer.
    soil, roots, stem, leaves

Check. Soil, roots, stem, leaves: the water reaches the leaves last. ✓

Watch out

Watch out: the water does not travel down the stem to the roots. It goes up. The roots take the water in, and the stem carries it up to the leaves.

Try it at home or school (with a grown-up). With a grown-up, put a celery stick in a clear glass of water with a few drops of food colouring. Leave it for an hour or two, and then look at the stick. Ask your grown-up to cut the stick across, and look at the coloured dots or lines. Do not drink the coloured water. Wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “Where did the blue colour start? Where has it got to now? Why did it go up the stick?” Let your child point with a finger from the glass, up the stick, to the leaves.

Exercise 3E  How water travels up the plant

1
FWater moves up the plant through tiny ___ in the stem. Write the missing word.
2
FWhat is the scientific name for the tubes that carry water up a plant? Write the name.
3
FWhat is the word for moving something from one place to another? Write the word.
4
FWater leaves a plant through tiny holes in its ___. Write the missing word.
5
FLook at the transport picture. Does the water move up the stem or down the stem? Write up or down.
water vapourwater moves uptiny tubesroots
6
FFill in the gaps.
(a)Water starts in the ___ and travels up the stem.
(b)Water is carried up to the ___ of the plant.
7
PSUse the celery table. Between which two times did the coloured water rise the most?
TimeHeight of coloured line
after 1 hour3 cm
after 3 hours9 cm
after 5 hours17 cm
8
PSMo says the coloured water rose 17 cm in the first 5 hours. Is Mo right? Write yes or no.
9
PSWorking scientifically. Predict: if a celery stick is put in red water instead of blue water, will the red colour reach the leaves? Write yes or no, and give a reason.
10
RExplain in one sentence why a cut stem would stop water reaching the leaves.
11
RKofi says the water in a plant only goes up, and never leaves the plant. Is Kofi right? Write no, and say how water leaves a plant.

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