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pull away from the cell wall. The salt or sugar solution slowly penetrates in
between the cell wall (light-colored lines) and the red cell. Perhaps you can
even observe how the cell contents turn a darker red over time. This is because
the red colorant in the cell becomes more concentrated after the loss of water
and hence becomes darker. If you don't take it too far, you can also reverse
the process. To do this, simply suck normal water up under the cover slip (see
"Staining Technique — Exchanging Solutions" on the previous page).
In Living Color
"Actually, a lion eats grass, too," says your biology teacher. What does he mean by
that? On TV, you may have seen how a lion devours a captured gazelle with great
skill. "Yes, but the gazelle got its flesh from eating plants." Ok, the gazelle is a
plant-eater and eats grass or leaves, for example. That is to say that it derives all
of its life-energy and the building material for its bodily cells from its plant diet.
The lion, on the other hand, lives from consuming all of the energy of the gazelle.
So when he eats the gazelle's flesh, he is essentially eating up the energy that was
stored in the gazelle's plant diet.
There are innumerable other examples to illustrate similar relationships. One
comes immediately to mind: A butterfly caterpillar is nibbling with pleasure on the
leaf of a lime tree. A bird snatches the caterpillar in an opportune moment. But
the bird can be eaten, too: If it isn't fast enough, it will be caught by a predator,
such as weasel. Biologists call this a food chain. Every living thing on Earth is part
of such a food chain, and there is always a plant at the beginning of a food chain
that, with its stored energy, serves as food for a plant eater.
But where does the plant get its life-energy? Plants are special organisms, because
they can do something that only they (and a few bacteria) are capable of: Plants
use the energy of the sun. Just imagine spending two hours in the sun each day
and being nourished for the rest of the day. That would be fantastic! All of the
world's nutritional problems would be solved if we were able, like plants, to eat
our fill of the sun's energy! We would just have to get used to one small detail:
People would all be green like plants!
The Chloroplasts
In the red onion, you got to know an example of why some plants or plant parts
are colored. A red colorant is dissolved in the cell sap of the onion skin. The color
of the blossom of the larkspur plant or the deep, dark red color of red cabbage
comes about in the same way. The green color in plants, however, comes from
something else. You will find small green granules in the plant cells of green plant
parts. These are chloroplasts. They are responsible for the green color of plants
and are also plants' fuel factories. With the help of the chloroplasts, the plant is
able to make use of the sun's energy to produce dextrose from carbon dioxide
(that's a component of the air surrounding us) and water. This process is called
photosynthesis. The energy that is stored in dextrose is used by the plant in order
to grow, bloom, and form fruit — or another creature makes use of the dextrose
in eating the plant. As a by-product of this unique process, oxygen also happens
to be produced too. So we don't live just from the sun's energy that is converted
by plants with their green leaves, but rather we also breathe in the by-product
that is formed in the process.
The cells of the red lily have a red cell sap. The
colored interior of the cell shrinks in a salt solu-
tion.
A food chain very
often has a plant at
its beginning.
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