Page 33 - 新思维科学学生用书8 样章

1 Respiration

The haemoglobin helps the red blood cells to transport oxygen.

• As the blood flows through the tiny capillaries next to the alveoli in the lungs, oxygen from the
air diffuses into the blood. Once it is in the blood, the oxygen then diffuses into the red blood
cells.
• Inside the red blood cell, the oxygen combines with haemoglobin.

It forms a very bright red compound called oxyhaemoglobin.
• As the blood continues on its journey around the body, it passes cells that are respiring. The
oxyhaemoglobin lets go of its oxygen and gives it to the cells.
• The blood, which has given away most of its oxygen, now travels back to the lungs to collect

some more.
This explains why red blood cells have haemoglobin – but why don’t they have a nucleus or
mitochondria? Scientists think that not having a nucleus makes more space for haemoglobin. They
also think that not having mitochondria stops the red blood cells from using up all the oxygen for

themselves, instead of delivering it elsewhere.

alveolus in lungs
blood containing a
oxygen di uses lot of oxygen flows
from alveolus away from lungs
into blood

haemoglobin in
red blood cells
picks up oxygen

blood containing haemoglobin in
a small amount of red blood cells
oxygen flows away gives away oxygen
from body cells

body cells

oxygen di uses
into body cells

How oxygen is transported around the body

Another way in which red blood cells are adapted for their function is that they are quite a lot
smaller than most cells in the body.

32