الأسبوع 8 · الفصل 6 «انتقال الماء في النباتات»: 6-1 النتح، 6-2 مسار الماء، مقال من نعم النيل · 3 دروس
1
Transpiration: water leaving the leaves
Science P6: Term 1, Chapter 6, pp. 54–61
GoalExplain transpiration and how a bag over leaves can show it.
New words
transpiration · water leaving a plant as water vapour, mostly through its leavesstomata · tiny pores, mostly under the leaveswater vapour · water as an invisible gas
Explanation
Plants take in water through their roots, but they do not keep all of it. Much of the water travels to the leaves and leaves the plant as water vapour through tiny pores called stomata. They are mostly on the underside of the leaves. This loss of water vapour from leaves is called transpiration. You can see it with an adult: tie a clear plastic bag around a leafy branch of a potted plant and put it in a sunny place. After a while, drops of water appear inside the bag. They came from the plant, not from a leak: the water vapour touched the cool plastic and turned back into drops. For a fair test, put a second bag on a plant with leaves removed or on a bare stem. Little or no water collects there.
Set-up
Drops inside the bag (expected)
Bag over a leafy plant
many
Bag over a bare stem
few or none
Worked examples
Habiba ties a clear bag around a leafy branch of a pot plant in the sun. After two hours there are drops on the inside of the bag. They show that the leaves lost water vapour.
Karim says: the water must be leaking out of the pot. His teacher shows a second bag on a pot with only a bare stem, with no drops. So the water came from the leaves.
On a hot, windy day, a plant loses water faster. This is why plants droop and need watering. After watering, a wilted plant often recovers.
Class activity
Bag test. With a grown-up, set up two bags: one on a leafy branch, one on a bare stem of a pot plant. Predict where drops will form. Check after two hours. Draw what you see and say what it means. Remove the bags afterwards so the plant does not get too hot.
Practice
1
What is transpiration?
Water leaving a plant as water vapour, mostly through the leaves.
2
What are stomata?
Tiny pores, mostly under the leaves.
3
Why did drops form inside the bag?
Water vapour from the leaves cooled and turned back into drops.
4
Why is a bag on a bare stem used?
To compare: it shows that the leaves are where most water leaves.
