Thames & Kosmos TK2 Scope, Руководство по эксперименту

Страница: 37 / 52

A watermelon is made of up to 95%
water. So it’s the ideal thirst-quencher
for hot summer days. But have you ever
wondered how the water gets into the melon
in the first place?
From the Ground into the Roots
Have you ever seen a tree that was uprooted by a storm? Thick, twisting roots
are visible. In the case of a stately oak tree, the ripped-out roots can sometimes
protrude upward over 2 meters. Even so, the parts of the root system exposed
here are only a tiny fraction of what’s under the ground. Even before the storm,
these powerful, wooden roots were no longer capable of absorbing water. They
merely served to anchor the tree in the ground. In order to absorb water, a tree
has extremely fine, microscopically small root hairs through which the groundwa-
ter is able to travel into the roots. But these root hairs are located at the very end
of the long root system and are so sensitive that they are mostly left behind when
the roots are torn out.
Root Hairs
It is generally not possible to pull a full-grown plant out of the Earth along
with the zone in which the root hairs are located. Consequently, you are better
off using the roots of seeds that have just sprouted. You will need:
• cress seeds (they can be found in the garden center or supermarket)
• an empty margarine tub (you can also use a small bowl or a saucer)
• cotton wool or tissues
• a slide and a cover slip
• the pipette and water
• a razor blade (see page 11)
• the tweezers
In order to get the cress seeds to germinate, place some cotton wool or tissues
into an empty margarine tub, wet it well with water, and place the seeds on
the wet cotton or paper. Put the tub in a window. After one or two days, the
first seeds will sprout, and little cress plants will emerge. As soon as you see
the first little white roots, you can remove a young germinating seedling and
separate the roots from the rest of the plant using a razor blade. Place the
root in a drop of water on the slide and cover the whole thing with a cover
slip. If the root is already too thick and the cover slip is somewhat raised as a
The root hair zone of a cress seedling
Root hairs of a cress plant
How Does Water Get
into a Watermelon?
11
37