B3.2.1 THE BLOOD SYSTEM
a) The circulatory system transports substances around the body.
b) The heart is an organ and pumps blood around the body. Much of the wall of the heart is made from muscle tissue.
c) There are four main chambers (left and right atria and ventricles) of the heart.
d) Blood enters the artia of the heart. The atria contract and force blood into the ventricles. The ventricles contracr and force blood out of the heart. Valves in the heart ensure that blood flows in the correct direction. Blood flows from the heart to the organs through arteries and returns through veins. There are two separate circulation systems, one for the lungs and one for all other organs of the body.
e) Arteries have thick walls containing muscle and elastic fibres. Veins have thinner walls and often have valves to prevent back-flow of blood.
f) If arteries begin to narrow and restrict blood flow stents are used to keep them open.
g) In the organs, blood flows through very narrow, thin-walled blood vessels called capillaries. Substances needed by the cells in body tissues pass out of the blood, and substances produced by the cells pass into the blood, through the walls of the capillaries.
B3.2.2 THE BLOOD
a) Blood is a tissue and consists of a fluid called plasma in which red blood cells, white blood cells, and platelets are suspended.
b) Blood plasma transports: carbon dioxide from the organs to the lungs. Soluble products of digestion from the small intestine to other organs. Urea from the liver to the kidneys/
c) Red blood cells transport oxygen from the lungs to the organs. Red blood cells have no nucleus. They are packed with a red pigment called haemoglobin. In the lungs haemoglobin combines with oxygen to form oxyhaemoglobin. In other organs oxyhaemoglobin splits up into haemoglobin and oxygen.
d) White blood cells have a nucleus. They form past of the body's defence system against microogranisms.
e) Platelets are small fragments of cells. They have no nucleus. Platelets help blood to clot at the site of a wound.
B3.2.3 TRANSPORT SYSTEMS IN PLANTS
a) Flowering plants have separate transport systems:
- xylem tissue transports water and mineral ions from the roots to the stem and leaves.
- the movement of water from the roots through the xylem and out of the leaves is called the transpiration stream
- phloem tissue carries dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs.