How water travels through a plant
Biology · Key Stage 2 · The School
Water has to travel
A plant's roots sit underground, in the soil. Its leaves sit up in the air and light. Water taken in by the roots has to reach the leaves. It has a long way to travel, straight up through the middle of the plant. In a tall tree, that journey can be many metres.
Tiny tubes inside the stem
Inside every stem are thin tubes. These tubes are called XYLEM. They run from the roots, up through the stem, all the way to the leaves. Water rises up through them, a little like water rising up a thin straw. You cannot see the tubes without cutting the stem open. A slice through celery shows them clearly.
Why the leaves need the water
Leaves use water to stay firm and upright. Without enough water, a leaf droops and goes limp. Water also escapes from tiny holes in the leaf as vapour. That loss pulls more water up from the roots behind it, like a slow, steady chain. This whole process has a name: transpiration. It goes on all day, in every leaf, on every plant.
Stand a white flower in water mixed with food colouring. Wait a few hours. Look closely at the petals. Streaks of colour appear, right along the veins. The coloured water travelled up through the xylem tubes in the stem, then out into the petals. You can now see, with your own eyes, the very path the water took, from the water right up to the flower. Try two colours in two vases, and each flower will show its own colour clearly.