Page 34 - 新思维科学学生用书8 样章

1.5 Blood

Being so small helps them to get through very tiny blood capillaries. This means they can get really

close to the alveoli in the lungs, and to the respiring cells in other parts of the body.

Question
3 Explain why red blood cells might use up oxygen, if they have mitochondria.

White blood cells

White blood cells are easy to distinguish from red blood cells.
They always have a nucleus, which red blood cells do not have. Some kinds of white blood cell – but
not all – are larger than red blood cells.

Some bacteria and viruses can cause illness when they get into the body. These bacteria and viruses
are called pathogens. White blood cells help to defend us against pathogens.

Some kinds of white blood cell can change their shape,

and push their cytoplasm out to make ‘fingers’ that can pathogen white
blood cell
capture a pathogen. The white blood cell then produces
chemicals that kill and digest the pathogen.

Other types of white blood cell produce chemicals that kill
pathogens. These chemicals are called antibodies. They are

shown as little Y-shapes on the diagram below. Different kinds
of antibodies are needed for each different kind of pathogen.

The antibodies stick onto the pathogen. Sometimes, they kill
the pathogen directly. Sometimes, they glue lots of the pathogens
together so that they cannot move. This makes it easy for

other white blood cells to capture and kill the pathogens.

1 Bacteria may get into the body.
Some kinds of of bacteria are
pathogens. They could make you ill.
2 Some kinds of white
blood cell make chemicals
called antibodies.
The antibodies
stick to the bacteria.

3 Sometimes, the antibodies simply kill
the bacteria. Sometimes, they stick
them together so that other white
blood cells can come and kill them.

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