A level biology

Cambridge International AS and A Level Biology build on the skills acquired at Cambridge IGCSE (or equivalent) level.

  • A level biology,  Biology

    Defences Against Diseases

    The body has three main lines of defence against disease. These involve mechanical barriers, chemical barriers and cells. Mechanical barriers Although many bacteria live on the surface of the skin, the outer layer of the epidermis seems to act as a barrier that stops them getting into the body. But if the skin is cut or damaged, the bacteria may get into the deeper tissues and cause infection. Hairs in the nose help to filter out bacteria that are breathed in. However, if the air is breathed in through the mouth, this defence is by-passed. Chemical barriers The acid conditions in the stomach destroy most of the bacteria that may…

  • A level biology,  Biology,  O level biology

    Sir Alexander Fleming

    (August 6 , 1881 – March 11, 1955) Early life and Education Sir Alexander Fleming was a Scottish physician, microbiologist, and pharmacologist, who was born on August 6, 1881 at Lochfield farm near Darvel, in Ayrshire, Scotland. Alexander was the third of four children of farmer Hugh Fleming (1816–1888) from his second marriage to Grace Stirling Morton (1848–1928). In December 1915, Fleming married a trained nurse, Sarah Marion McElroy of Killala, County Mayo, Ireland. Their only child, Robert Fleming (1924–2015), became a general medical practitioner. After his first wife’s death in 1949, Fleming married Dr. Amalia Koutsouri-Vourekas, a Greek colleague at St. Mary’s, on 9th April 1953; she died in…

  • A level biology,  Video Notes


    If a dilute solution is separated from a concentrated solution by a partially permeable membrane, water diffuses across the membrane from the dilute to the concentrated solution. This is known as osmosis. A partially permeable membrane is porous but allows water to pass through more rapidly than dissolved substances. Since a dilute solution contains, in effect, more water molecules than a concentrated solution, there is a diffusion gradient which favours the passage of water from the dilute solution to the concentrated solution. In living cells, the cell membrane is partially permeable and the cytoplasm and vacuole (in plant cells) contain dissolved substances. As a consequence, water tends to diffuse into…