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A tree's roots take up water and minerals from the soil. Most of the big roots are near the surface, in the top 30 cm or so, and they often spread wider than the branches.

Inside the trunk, a layer called the xylem (sapwood) carries water up to the leaves. The phloem (inner bark) carries the food made in the leaves to the rest of the tree.

Leaves make food by photosynthesis: they use light energy to turn carbon dioxide and water into sugar, and they give out oxygen. The green pigment chlorophyll captures the light.

Experiment: Fair test: catching transpiration

1. Choose two leafy branches on the same tree: one in the sun and one in the shade.
2. Choose a third twig and gently pinch off its leaves, or use a twig that has none.
3. Weigh three dry paper towels, put one in each bag, then slide each bag over a branch so the leaves are inside. Tie loosely.
4. Predict which bag will collect the most water.
5. After 2–3 hours, look for droplets. Take the bags off and weigh the damp paper towels (or compare how wet they look).
6. Remove all bags and string from the tree.

Branch	Droplets? (none / some / lots)	Water in towel (g)
Leafy, sunny	Prediction
Leafy, shady	Prediction
No leaves	Prediction

Questions

1. Describe the journey of water from the soil to the air through a tree. Use the words roots, xylem, leaves and stomata.

2. Which bag collected the most water in your test? Why?

3. A large oak gives off about 151,000 litres of water a year. About how much is that per day? (Hint: divide by 365.)

4. A tree stump has 64 rings. About how old was the tree? Some rings are narrow: what might that mean?

Sources for every fact on this sheet: echoesof.science/school/trees/sources/

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