Xylem and phloem

Plants need water, for photosynthesis and much more. Roots take up water from the soil, along with minerals dissolved in it; minerals are important nutrients for growth. Roots branch out a lot, which lets them touch more soil and soak up more water. But how does that water get from the roots all the way to the leaves?

Activity 10.7 shows it. Fill two tumblers A and B one-third with water, and add a few drops of red ink to B. Cut the stems of two similar tender plants slantwise, under water — preferably plants with white flowers, such as white sadabahar or balsam, so the colour shows — and put one in each tumbler.

Next day, the twig in B has red in its stem, its leaves and even its flowers. The twig in plain water does not.

Now cut the stem of that twig higher up, above the coloured water, and look at the cut end through a magnifying glass. You can see red inside the stem.

How did the ink climb up? Through thin tube-like structures called xylem, found in the stem, branches and leaves. Just like the red ink, water and dissolved minerals travel up through the xylem to the leaves and other parts.

Food travels a different way. The food made in the leaves is carried to all parts of the plant through another set of thin tubes called phloem. (A memory trick: phloem and food start with the same sound.) Some of this food is stored in parts such as seeds and roots.