How a tree works

Lesson page: echoesof.science/school/trees/ages-10-11/ · Pupil worksheet: echoesof.science/school/trees/ages-10-11/print/

Learning aims

Describe how water moves through a tree and leaves through stomata (transpiration).
Know that leaves make sugar and oxygen by photosynthesis.
Explain autumn colour and leaf fall in simple terms.
Use tree rings to estimate age.

Lesson plan

Time	Activity
5 min	Starter: how does water get to the top of a tall tree without a pump?
10 min	Set up the bag test (check after lunch).
15 min	Read the text; look at a log slice or photo of rings.
5 min	In or out? game.
5 min	Quiz.
5–10 min	Check bags and do the worksheet.

Materials for the experiment

Three clear plastic food bags
Soft ties or string
Small tree or shrub branches in the school grounds (with permission)
Paper towels
A kitchen scale (optional)

Safety: Ask permission before using a tree. Avoid plants you do not know (some are poisonous or irritate skin) and wash hands afterwards. Never put plastic bags over heads. Take all bags and ties away at the end.

Common misconceptions

Pupils may think…	Actually…
Trees get their mass from the soil.	Most of the material for growth comes from carbon dioxide taken from the air in photosynthesis; roots take up water and minerals.
Leaves turn red and yellow because they die of cold.	The tree seals off each leaf; chlorophyll fades and other pigments show.
Water goes up the trunk in the bark.	Water goes up in the xylem (sapwood); the inner bark (phloem) carries food.

Worksheet answers

Water enters the roots from the soil, travels up the xylem in the trunk and branches to the leaves, and escapes as water vapour through the stomata.
Answer from the class results. The bare twig should collect least, because water vapour escapes mainly through the leaves' stomata; compare the sunny and shady bags to see the effect of light and warmth.
About 151,000 ÷ 365 ≈ 410 litres a day.
About 64 years. Narrow rings can mean a poor growing year, for example a drought or a severe winter.

Quiz answers

Which layer carries water up the trunk? Xylem (sapwood). Xylem carries water and minerals from the roots to the leaves.[1]
What do leaves give out during photosynthesis? Oxygen. Photosynthesis makes sugar and releases oxygen.[3]
What are stomata? Tiny holes in leaves. Gases go in and out of leaves through stomata.[3]
Why do leaves turn yellow in autumn? The green chlorophyll fades and hidden yellow shows. Yellow carotenoids are there all summer, masked by green.[6]
What does one tree ring usually show? One year of growth. A tree normally adds one ring each year.[4]
In the bag test, which branch should collect least water? The twig with no leaves. Water vapour leaves mainly through the leaves.[5]

Going further

Collect leaves from evergreen and deciduous trees and compare thickness, shape and waxiness. Which might lose less water in winter?

Sources used in this lesson

[1] Parts of a tree (Minnesota Department of Natural Resources (Forest Treasures)): reliability High
[2] Tree (Britannica Kids (Encyclopaedia Britannica)): reliability High
[3] Biology 2e, 8.1 Overview of photosynthesis (OpenStax (Rice University)): reliability High
[4] Tree rings and climate (UCAR Center for Science Education): reliability High
[5] Evapotranspiration and the water cycle (U.S. Geological Survey, Water Science School): reliability High
[6] Color changes in autumn leaves (Clemson Cooperative Extension, Home & Garden Information Center): reliability High
[7] About the trees (Redwood National and State Parks) (U.S. National Park Service): reliability High
[8] The Prometheus story (U.S. National Park Service, Great Basin National Park): reliability High

Full list with links and a note on each source's reliability: echoesof.science/school/trees/sources/

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