Science Focus 4.3
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
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What is blood?
Blood carries water, oxygen and the nutrients to cells around the body. It also removes carbon dioxide and waste material from those cells and maintains our body temperature.
How much blood does the average human body contain?
About 5.5 litres
What is blood made up of?
red and white blood cells, platelets and plasma.
Where are red blood cells made?
in bone marrow
Red blood cells have no nucleus, allowing them to carry more of a substance called what?
haemoglobin
Haemoglobin attracts and carries ______ and contains ____, which gives blood its red colour.
oxygen; iron
Blood containing oxygen is what colour?
Bright red. (Blood without oxygen is a much duller red (blue).)
Red blood cells last for about ___ days.
100
One drop of blood contains about how many red blood cells?
5 million
White blood cells are _____ than red blood cells, and have a ______.
bigger; nucleus
Our bodies have far fewer white blood cells that red ones. A drop of blood contains about ____ white cells.
3000
White blood cells help rid the body of harmful _______ and _______ by surrounding and destroying them, or by producing chemicals to kill them.
bacteria; viruses
Platelets have no nucleus, and help trigger formation of ______ strands, which help blood to ____.
fibrin; clot
What is Plasma?
Plasma is a clear, yellow liquid in which red and white cells and platelets are suspended.
Plasma is 90 per cent _____.
water (The rest is dissolved food, waste products and body chemicals called hormones.)
Blood Type. Blood contains, at most, two types of ______, known as ________ and ________.
antigen; antigen A; antigen B. (Antigens are special chemicals involved in fighting microorganisms in the blood.)
Type A blood contains ______, type B blood contains _______, type AB blood contains _____ and type O blood contains _____.
antigen A; antigen B; both; neither
What is the most common type of blood?
type O positive
Rhesus factor. Rhesus is another type of ______.
antigen
Blood that contains the Rhesus antigen is classified as ___________. Blood without the Rhesus antigen is classified as ___________.
Rhesus positive (or Rh positive); Rhesus negative
For a blood transfusion to be safe, the donor blood must not contain any _______ that are not already in the patient’s blood, otherwise blood cells may clump together and form deadly blockages.
antigens (The Rhesus factors must also match.)
The human heart is really two pumps joined together that do separate jobs. One pump sends blood to the _____ to pick up oxygen. The other receives the oxygen-carrying blood and pumps it to the _____ and around the ____.
lungs; head; body
Blood that is rich in oxygen is said to be _______, while blood that has had most of its oxygen removed is _______.
oxygenated; deoxygenated
Each half of the heart, or each pump, has two main sections or chambers: the ______, where blood enters, and the ________, where blood is pumped out.
atrium; ventricle