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Grade 7 Beginner About 15 min Version 1 Awaiting review Premium

How does water travel up a stem?

Plants take in water through their roots and carry it up the stem to the leaves in tiny tubes called xylem. As water evaporates from the leaves (transpiration), more water is pulled up the xylem behind it, rather like drinking through a straw. Coloured water makes the xylem visible: cut across the stem and you see the tubes as coloured dots. The more water the leaves lose, the faster the water rises.

What you will learn

  • Show that water travels up a stem in xylem tubes.
  • Explain how leaves help pull water up the stem.
  • Describe how warm, sunny conditions speed up water transport.

Before you start

  • Know the main parts of a plant.

Materials

  • Fresh celery stalks with leaves (or white flowers such as carnations)
  • Red food colouring and water

Equipment

  • Glasses, a ruler and a knife (used by the teacher)

Procedure

  1. Stand a leafy celery stalk in red water in a warm sunny place. Record the height of the dye after 15, 60 and 120 minutes.
  2. Repeat in a cool shady place.
  3. Repeat with the leaves removed.
  4. Cut across the stalk and look at the cross-section.

How this simulation is simplified

  • The stalk is 150 mm tall. Dye climbs 2.5 mm a minute with leaves in a warm sunny place; each change slows this by a fixed amount.