bio F.3 help

first of all you should know about the exchange in substance in the capillaries
at the arterial end of the capillaries
the blood pressure is very high because the blood is come from the artery
which is pumped from the heart
due to this pressure difference
some substances in the blood will be forced out through the capillaries wall
oxygen is one of these substances
it forced out to supply the cells for respiration
also, at the same time, some substances will pass into the capillaries, and to the blood
carbon dioxide is one of these substances
that is, the oxygen level in the blood will drop from the arterial end of the capillaries
to the venous end
and the carbon dioxide level in the blood will rise from the arterial end of the capillaries
to the venous end

please don't mind I explain in Chinese
因為blood capiliaries係進行物質交換,包括礦物質同代謝廢物,而CO2係代謝廢物,所以CO2 low concentration 係好正常,
而負責帶氧的係artery,而唔係微血管,所以 blood capiliaries 的氧含量係好低。