A level biology

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

  • A level biology,  A level biology,  Biochemistry,  Biology,  Cell biology,  O level biology,  Q & A

    What is enzyme and characteristics?

    Enzymes are biological catalysts that facilitate chemical reactions in living organisms. They are typically proteins, although some RNA molecules also have catalytic activity. Enzymes are essential for life because they speed up the reactions that are necessary for cells to function properly. Without enzymes, many biochemical reactions in the body would occur too slowly to support life. Enzymes work by lowering the activation energy required for a chemical reaction to occur. Activation energy is the amount of energy needed to start a reaction, and enzymes reduce this energy barrier, allowing the reaction to occur more quickly. Enzymes do this by binding to specific molecules, called substrates, and positioning them in…

  • A level biology,  Biology,  O level biology,  Zoology

    Why Earthworms Are a Gardener’s Best Friend

    Earthworms are considered a gardener’s best friend for several reasons: Soil aeration: Earthworms burrow through the soil, creating tunnels and air pockets that allow air, water, and nutrients to penetrate the soil more easily. This improves soil aeration, which is important for plant root health. Soil structure: Earthworms also help to improve soil structure by breaking down organic matter and creating channels for water to flow through. This creates a more hospitable environment for plant roots to grow. Nutrient cycling: As earthworms eat their way through the soil, they break down organic matter and release nutrients that plants can use. They also excrete castings (worm poop) that are rich in…

  • plasma-membrane
    A level biology,  A level biology,  Biochemistry,  Biology,  Cell biology,  O level biology

    Plasma membrane

    Delimiting membrane or boundary of all cells providing the characteristic shape to the cell. Structure ● Composed of approx. 7 nm thick phospholipid bilayer with hydrophilic heads facing outward from both sides into aqueous environment and hydrophobic tails facing inside the bilayer. ● A symmetrical the presence of proteins, floating in the bilayer imparts a fluid mosaic pattern which comprises of (a) Integral/Intrinsic proteins spanning through the lipid bilayer, protruding both extracellular and cytoplasmic sides of membrane. (b) Peripheral/Extrinsic proteins located on outside either extracellular or cytoplasmic surface. (c) Lipid anchored proteins covalently linked to a lipid molecule of bilayer but present outside to it. ● Some oligosaccharides are covalently…

  • mutation
    A level biology,  A level biology,  Biochemistry,  Biology,  Cell biology,  Genetics,  O level biology


    Mutation is a change in the DNA sequence of an organism’s genetic material. DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions for the development and function of all living things. DNA is made up of four chemical bases, adenine (A), cytosine (C), guanine (G), and thymine (T), which are arranged in a specific sequence to form genes. Genes are the functional units of DNA that encode specific traits and are passed on from parent to offspring. In biology, mutations can occur naturally or as a result of exposure to certain environmental factors such as radiation or chemicals. Natural mutations can arise from errors during DNA replication…

  • chromosome
    A level biology,  A level biology,  Biochemistry,  Biology,  Cell biology,  Genetics,  O level biology


    A chromosome is a structure found in cells that is made up of a long strand of DNA, which is the genetic material that contains the instructions for the development and function of all living organisms. Chromosomes are found in the nucleus of eukaryotic cells and play a crucial role in the cell cycle, replication, and transmission of genetic information. Chromosomes are tightly coiled, compact structures that can be seen under a microscope during cell division. The DNA in chromosomes is organized into segments called genes, which contain the instructions for making proteins and other essential molecules for life. Proteins play a critical role in many cellular processes, such as…

  • 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…