Science

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    • Use SI units (eg kg, g, mg; km, m, mm; kJ, J) and IUPAC chemical nomenclature unless inappropriate
    • Specialised cell
      As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function
    • Microscopy techniques
      • Electron microscopy has higher magnification and resolving power than a light microscope
      • Electron microscopy enables biologists to see and understand many more sub-cellular structures
    • Calculating magnification
      Magnification = size of image / size of real object
    • The nucleus of a cell contains chromosomes made of DNA molecules, and each chromosome carries a large number of genes
    • In body cells the chromosomes are normally found in pairs
    • Cell cycle and mitosis
      1. Genetic material is doubled and then divided into two identical cells
      2. Cell grows and increases sub-cellular structures
      3. DNA replicates to form two copies of each chromosome
      4. One set of chromosomes is pulled to each end of the cell and the nucleus divides
      5. Cytoplasm and cell membranes divide to form two identical cells
    • Stem cell
      An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation
    • Stem cell functions

      • In embryos
      • In adult animals
      • In the meristems in plants
    • Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells
    • Stem cells from adult bone marrow can form many types of cells including blood cells
    • Meristem tissue in plants can differentiate into any type of plant cell, throughout the life of the plant
    • Stem cell use
      May help treat conditions such as diabetes and paralysis
    • Therapeutic cloning

      An embryo is produced with the same genes as the patient, so stem cells from the embryo are not rejected by the patient's body and may be used for medical treatment
    • The use of stem cells has potential risks such as transfer of viral infection, and some people have ethical or religious objections
    • Stem cells from meristems in plants can be used to produce clones of plants quickly and economically
    • Uses of plant stem cell cloning
      • Protect rare species from extinction
      • Produce large numbers of identical crop plants with special features such as disease resistance
    • Diffusion
      The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
    • Substances transported by diffusion
      • Oxygen and carbon dioxide in gas exchange
      • Waste product urea from cells into the blood plasma for excretion in the kidney
    • Factors affecting rate of diffusion
      • Concentration gradient
      • Temperature
      • Surface area of the membrane
    • A single-celled organism has a relatively large surface area to volume ratio, allowing sufficient transport of molecules into and out of the cell to meet the needs of the organism
    • In multicellular organisms, surfaces and organ systems are specialised for exchanging materials to allow sufficient molecules to be transported into and out of cells for the organism's needs</b>
    • The effectiveness of an exchange surface is increased by having a large surface area, a thin membrane to provide a short diffusion path, an efficient blood supply, and (for gaseous exchange) being ventilated
    • Osmosis
      The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
    • Active transport
      Moves substances from a more dilute solution to a more concentrated solution (against a concentration gradient), requiring energy from respiration
    • Processes of transport into and out of cells
      • Diffusion
      • Osmosis
      • Active transport
    • Cells are the basic building blocks of all living organisms
    • Tissue
      A group of cells with a similar structure and function
    • Organ
      Aggregations of tissues performing specific functions
    • Organ system
      Organs organised to work together to form organisms
    • The digestive system is an organ system in which several organs work together to digest and absorb food
    • Enzymes catalyse specific reactions in living organisms due to the shape of their active site
    • Lock and key theory
      A simplified model to explain enzyme action
    • Digestive enzymes
      • Carbohydrases (break down carbohydrates to simple sugars)
      • Amylase (breaks down starch)
      • Proteases (break down proteins to amino acids)
      • Lipases (break down lipids to glycerol and fatty acids)
    • The products of digestion are used to build new carbohydrates, lipids and proteins, and some glucose is used in respiration
    • Bile
      Made in the liver and stored in the gall bladder, it is alkaline to neutralise hydrochloric acid from the stomach and emulsifies fat to form small droplets which increases the surface area and rate of fat breakdown by lipase
    • The heart is an organ that pumps blood around the body in a double circulatory system, with the right ventricle pumping blood to the lungs and the left ventricle pumping blood around the rest of the body
    • Blood vessels associated with the heart
      • Aorta
      • Vena cava
      • Pulmonary artery
      • Pulmonary vein
      • Coronary arteries
    • The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker, and artificial pacemakers are electrical devices used to correct irregularities in the heart rate
    • Types of blood vessels
      • Arteries
      • Veins
      • Capillaries