• 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…

  • MCQ

    Which of these cells are not a type of neuroglia found in the CNS

    Option C: Schwann cell is the right answer. There are three types of glial cells in the mature central nervous system:  astrocytes, oligodendrocytes, and microglial cells. Astrocytes, which are restricted to the brain and spinal cord, have elaborate local processes that give these cells a starlike appearance. The major function of astrocytes is to maintain, in a variety of ways, an appropriate chemical environment for neuronal signaling. Oligodendrocytes, which are also restricted to the central nervous system, lay down a laminated, lipid-rich wrapping called myelin around some, but not all, axons. Myelin has important effects on the speed of action potential conduction. In the peripheral nervous system, the cells that elaborate myelin are called…

  • How-do-plants-know-when-to-flower
    Biology,  Botony

    How do plants know when to flower?

    Phytochrome, a blue-green pigment, is part of a switching mechanism for phototropic responses to light of red and far-red wavelengths. Its active form, Pfr might trigger the secretion of one or more hormones that induce and inhibit flowering at different times of yeat. The main environmental cue for flowering is the length of night, i.e. the hours of darkness, which vary seasonally. Different kinds of plants from flowers at different times of years, depending on their phytochrome mechanism. Products of a set of master gene govern flower formation by selectively acting on meristematic cells of floral shoots. The study of mutants of common wall cress, Arsbidopsis thaliana, supports an ABC…

  • 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…