Biology Revision for "O" level examinations

Red Blood cells/erythrocytes -they are formed in red bone marrows of the ribs, skull and vertebrae -survive for approximately 120 days and are then destroyed in the liver and spleen Structure and Function -contains no nucleus: this allows more room for haemoglobin (also: cells cannot divide/reproduce ) -they have biconcave disc shape to increase surface area -contains hemoglobin that allows the transport of oxygen White Blood cells/Leucocytes a. Phagocytes Function: They engulf and digest invading bacteria and viruses.   Structure:             -their shape may vary             -they move using pseudopodia             -its nucleus is lobed shape             -they are formed in red bone marrows             b. Lymphocytes Structure:          -round, large cells                         -large, round nucleus                         -they are made in lymph glands and spleen

Hypertension •          B lood flows through the blood vessels with a force greater than normal i.e. with a blood pressure reading of 140/90 •          When the blood pushes harder against the walls of your arteries, your blood pressure goes up Prevention •          Quit smoking •          Exercise regularly •          Reduce amount of sodium •          Eating a healthy diet Coronary Heart Disease/ Heart  attack •          A heart attack happens when the flow of oxygen-rich blood to a section of heart muscle suddenly becomes blocked and the heart can’t get oxygen. •          If blood flow isn’t restored quickly, the section of heart muscle begins to die. •          Coronary Heart disease •          CHD is a condition in which plaque builds up inside the coronary arteries. •          When plaque builds up in the arteries, the condition is called  atherosclerosis •          The buildup of plaque occurs over many years. •          Coronary thrombosis-

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