Page 31 - 新思维科学学生用书8 样章

1 Respiration

Delivering the requirements for respiration in cells

You have seen that all of your cells need energy to stay alive. Each cell gets its energy through a
chemical reaction called respiration.

Aerobic respiration happens inside the mitochondria in the cells. The reactants are glucose and

oxygen:

glucose + oxygen → carbon dioxide + water

So every cell in your body needs a good supply of glucose and oxygen, and the carbon dioxide and
water that the cell makes must be taken away. The delivery and removal is done by the blood.

The blood moves around the body inside blood vessels. The heart pumps constantly, to keep the

blood moving.

What is blood?

Everyone knows that blood is a red liquid. But if you are able to look at some blood through a
microscope, you may get a surprise. The photograph shows what you might see.

This is the liquid part of the blood. This liquid
is called blood plasma. You can see that it is
not red at all. It is a very, very pale yellow.

Blood looks red because it contains a lot of
red blood cells, which float in this liquid.
Most of the cells in our blood are red blood
cells. An adult person has at least 20 trillion red
blood cells in their body. There are about five
million of them in every 1 cm of your blood.
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These are called white blood cells. There are
not many of them, but some of them may be
quite a lot bigger than the red blood cells.
They don't look white in the photograph
because a stain has been added to the blood,
to make the cells show up more clearly.
The dark purple areas in these cells are their
nuclei. (Red blood cells don’t have nuclei.)

Blood viewed through a microscope

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