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SavannahYear 8
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SciencePlants: the quiet engines30 min★★ difficulty

Water's climb: roots, xylem and stomata

A tall oak moves hundreds of litres of water a day from soil to sky with no pump. This lesson explains the plumbing — and the tiny doors that control it.

Lesson overview

What you'll learn in this lesson

Understand the role of leaf stomata in gas exchange in plants and the dependence of almost all life on Earth on the ability of photosynthetic organisms to use sunlight

Key learning points

  • • Pull, not push
  • • What speeds transpiration up
  • • Stomata: open for business, closed for drought
  • • Why we are here at all

This lesson at a glance

  • 30 minutes
  • 20 parts to scroll through
  • 4 quick checks
  • Marked quiz at the end
  • Gentle pace: short sittings with pauses

Words to know

stomataexchangeplantsdependencealmost

Scroll down — the lesson carries on below

Part 1 of 20 · Discover5%
1

Watch & discover

Part 1 of 20

Watch first

Water's climb: roots, xylem and stomata

An English teaching video on this topic from Archie Science Show. Watch it, then scroll down for the lesson.

In a nutshell

Understand the role of leaf stomata in gas exchange in plants and the dependence of almost all life on Earth on the ability of photosynthetic organisms to use sunlight

2

What you already know

Part 2 of 20

Before we start

What you already know

You know the word equation for photosynthesis and that leaves have pores called stomata.

Recap: How a leaf eats sunlight
3

Key words

Part 3 of 20

Key words

Words you'll need today

xylem
Dead, hollow tubes that carry water up from the roots.
transpiration
The loss of water vapour from a leaf, which pulls more water up behind it.
guard cells
Pairs of cells that open and close each stoma.
4

Learning cycle

Part 4 of 20

Learning cycle 1 of 2

Part 1 — The upward river

A short piece of teaching, then a check to make sure it has landed.

5

Explore the idea

Part 5 of 20

Learn

Pull, not push

Water evaporates from the surfaces inside a leaf and escapes through the stomata. Each escaping molecule tugs the one behind it, and because water molecules stick together, the whole column in the xylem is pulled upward — like sucking a drink through a straw that runs the full height of the tree.

6

Explore the idea

Part 6 of 20

Learn

What speeds transpiration up

Four things make the river run faster: heat (faster evaporation), wind (carries the vapour away), low humidity (dry air pulls harder), and light (stomata open for photosynthesis). A hot, windy, sunny day is when a tree works hardest — and when gardeners water most.

7

Quick check

Part 7 of 20

Quick check

The force that moves water up a tree comes from...

8

Quick check

Part 8 of 20

Quick check

Which condition slows transpiration?

9

Reset break

Part 9 of 20

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now
10

Learning cycle

Part 10 of 20

Learning cycle 2 of 2

Part 2 — The doors in the leaf

A short piece of teaching, then a check to make sure it has landed.

11

Explore the idea

Part 11 of 20

Learn

Stomata: open for business, closed for drought

Guard cells swell with water to bend apart and open the pore, and go limp to close it. Open stomata let carbon dioxide in for photosynthesis but leak water. In a drought the plant closes them and saves water — but stops feeding. Every leaf is making this trade-off all day.

12

Explore the idea

Part 12 of 20

Learn

Why we are here at all

Photosynthetic organisms — plants on land, algae in the sea — made the oxygen atmosphere and still restock it. Almost every food chain on Earth starts with sunlight caught by something green. When you look after plants, you are looking after the base of everything.

13

Quick check

Part 13 of 20

Quick check

Guard cells open a stoma by...

14

Quick check

Part 14 of 20

Quick check

A plant closing its stomata in a drought saves water but...

15

Investigate evidence

Part 15 of 20

Evidence 1 of 1

primary

Transpiration measurements from a potometer

KS3 science class investigation, School laboratory record

Bubble moved 24 mm in 10 minutes in still air; 41 mm with a fan blowing; 18 mm with a plastic bag tied over the leaves; 37 mm under a bright lamp.

A potometer measures how fast a leafy shoot takes up water, which tracks how fast water is evaporating from its leaves — transpiration.

Think like a historian

Which condition sped up water loss the most, and which slowed it down? Use the idea of stomata opening and closing to explain both results.

Source: Class practical results table, a standard KS3 investigation.

View the archive record ↗
16

Common mix-ups

Part 16 of 20

Common mix-ups

Things people often get wrong

  • Thinking roots suck water up like a pump — the pull comes from the leaves.
  • Thinking stomata are always open — they close at night and in drought.
  • Confusing xylem (water, upward) with phloem (food, both ways).
17

Challenge round

Part 17 of 20

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

18

Challenge round

Part 18 of 20

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

Water evaporates from the surfaces inside a leaf and escapes through the ____.

Photosynthetic organisms — ____ on land, algae in the sea — made the oxygen atmosphere and still restock it.

____ every food chain on Earth starts with sunlight caught by something green.

19

Mastery quiz

Part 19 of 20

Marked quiz

End of lesson quiz: Water's climb: roots, xylem and stomata

3 questions, marked with the reasoning shown. No timer.

  1. 1. Water travels up a plant in the...

  2. 2. Transpiration is fastest on a day that is...

  3. 3. Almost all life depends on photosynthetic organisms because they...

20

Lesson round-up

Part 20 of 20

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

0

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

  1. Name the variable the club changed the second time, and one variable they kept the same.
  2. Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
  3. Write a conclusion for the club's report, saying how far the evidence supports it.

Source for this lesson

Use this for the source work task below.

Transpiration measurements from a potometer

primary

KS3 science class investigation, School laboratory record

Bubble moved 24 mm in 10 minutes in still air; 41 mm with a fan blowing; 18 mm with a plastic bag tied over the leaves; 37 mm under a bright lamp.

A potometer measures how fast a leafy shoot takes up water, which tracks how fast water is evaporating from its leaves — transpiration.

Source: Class practical results table, a standard KS3 investigation.

View the original record ↗

  • Method and results

    Writing

    Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.

    1 page + results table

  • Conclusion

    Writing

    Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.

    6–8 sentences

  • Labelled diagram

    Diagram

    Draw the apparatus or the process in pencil, label it fully, and photograph it.

    1 labelled diagram

  • Reading and notes

    Reading

    Read the lesson text again and write the key ideas in your own words.

    Half a page of notes

Saved as you type.

Part 1 of 20 · Watch & discover

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