• 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…

  • Q & A on cytplasm

    Q & A on Components of Cytoplasm

    Which organelle divides and compartmentalizes the cell?  The endomembrane system, which fills the cell and divides it into compartments, and is visible only through electron microscopy. The endoplasmic reticulum (ER), a series of interconnected membranous tubes and channels in the cytoplasm, is the largest and most extensive system of the internal membranes. What is the function of the endomembrane system? The endomembrane system allows macromolecules to diffuse or be transferred from one of the components of the system to another. What is the difference between rough and smooth endoplasmic reticulum? Rough endoplasmic reticulum are regions rich in ribosomes that manufacture proteins. These regions appear to have a pebbly surface that is somewhat similar to sand-paper.…

  • Zoology

    Phylum Hemichordata

    Phylum Hemichodata Hemichordates are vermiform, solitary or colonial enterocoelous coelomate animals having intra-epidermal nervous system and a pre-oral gut with or without gillslits and without typical nephridia. Due to some similarities with chordates, some workers (Bateson, 1885) considered Hemichordata as a subphylum of the phylum Chordata. Alliance with the chordates was based on the presence of gill slits and the so called ‘notochord’. It is now generally agreed that the hemichordate “notochord” is neither analogous nor homologous with the chordate notochord and that except the common possession of pharyngeal clefts the two groups are dissimilar. On grounds of its similarities with invertebrates some recent scientists, like Van der Horst (1939),…

  • MCQ

    MCQ on Breathing and Exchange of Gases

    Dead space air is  The amount of air left in lungs after deepest expiration.  About 150 ml  Both of these  None of these Answer: 2 The amount of air left in the lungs after the deepest expiration is Residual air.  2. When fully saturated, one molecule of oxyhaemoglobin carries the following number of oxygen molecules.  Two  Three  Four  None of these  Answer: 3 One molecule of Haemoglobin contains four molecules of Haem, so four iron atoms, for carrying for molecules of Oxygen 3.Which of the following breathing process in human is passive  Expiration Aspiration  Inspiration  Forced breathing  Answer: 1 4. The amount of oxygen in tidal vol. is approximately  1…

  • Flashcard,  Genetics

    Genetics Terms Flashcard

    Genetics Genetics is the study of inheritance and variation. Term genetics was first used by W. Bateson 1905. Gregor Johann Mendel is called the father of genetics. Heredity or inheritance Heredity or inheritance is the process by which characters are passed on from parent toprogeny Variation Variation is the characteristic difference by which progeny differs from their parents. Cause of variation is sexual reproduction. Phenotype External appearance or trait of an individual. Genotype Genetic constitution of an organism Genes or mendelian factor Units of inheritance. They contain the information required to express a particular trait Alleles or allelomorphs The two Mendelian factors or gene which occur on the same locus…