Biology Unit 8

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  • Created on: 21-12-10 23:00

GCSE Revision Notes                                                                       (t/b  p 80 – 91,   283 – 295 )

Unit 8                         BLOOD  AND IMMUNITY  


Functions of the circulatory system

  1. Transport – oxygen, carbon dioxide, digested food, urea.
  2. Protection – blood clotting, production of antibodies.
  3. Body temperature – this is maintained at 37 0C.


Structure of the blood

Red blood cells (erythrocytes) –  no nucleus, biconcave discs, contain haemoglobin. This allows for the easy diffusion and transport of oxygen.

                                               Oxygen collected at lungs

                                              Oxygen released at cells


White blood cells  (leucocytes)

    Phagocytes -  engulf and digest other dead cells, bacteria etc.

                       -  irregular shape means they can squeeze through the capillary walls

                       -  lobed nucleus.

    Lymphocytes -  produce antibodies

     - large round nucleus.


Platelets - blood clotting. These tiny cell fragments release an enzyme that changes a blood protein fibrinogen into long threads of fibrin. These threads block the wound.


Plasma  - this is the straw coloured liquid of the blood. It transports dissolved materials e.g carbon dioxide, glucose, urea, hormones etc.


The Heart


Double circulation – the blood goes through the heart twice in one complete circuit of the body.


Pathway of blood through the heart

·      Deoxygenated blood in the vena cava flows from the body into the right atrium.

·      The right atrium contracts and forces blood into the right ventricle through a valve.

·      The right ventricle contracts and forces blood through a valve to the lungs in the pulmonary artery.

·      The oxygenated blood returns from the lungs in the pulmonary vein and enters the left atrium.

·      The left atrium contracts and forces blood into the left ventricle through a valve.

·      The left ventricle contracts and forces blood through a valve into the aorta and then to the rest of the body.

Note : Valves ensure blood flows one way through

                                                                                        The heart.                                                                                                         

Note : left ventricle  has thicker walls than right ventricle because it has to pump blood all round the body



Blood vessels 





Carry blood away from the heart

Carry blood to the heart

Connect arteries to veins in the organs of the body

Carries oxygenated blood

(exception-pulmonary artery)

Carries deoxygenated blood

(exception- pulmonary vein)

Oxygen diffuses out to the cells

Carbon dioxide diffuses into the capillary

No valves

Valves to prevent backflow

No valves


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