Definitions - key concepts in biology

• Acrosome


  An organelle in the tip of a sperm that contains enzymes which digest the egg cell membrane
• Active site


  A specific region on an enzyme where the substrate binds and the reaction takes place
• Active transport


  The movement of substances from a low concentration to a higher concentration (against the concentration gradient) across a membrane, with the use of energy from respiration
• Benedict's test


  A chemical test used to test for reducing sugars that produces a different colour based on the amount of reducing sugar present
• Biuret test


  A chemical test that produces a purple colour when it is added to a solution containing protein
• Calorimetry


  A method of measuring heat transfer during a chemical reaction
• Carbohydrases


  Enzymes that break down carbohydrates into simple sugars
• Carbohydrate


  A large molecule that is synthesised from simple sugars
• Cell


  The basic building block of all living organisms
• Cell membrane


  A partially permeable barrier that surrounds the cell
• Cell wall


  An outer layer made of cellulose that strengthens plant cells
• Chloroplast


  An organelle that is the site of photosynthesis
• Chromosome


  A long, coiled molecule of DNA that carries genetic information in the form of genes
• Cilia


  Hair-like structures found on ciliated epithelial cells which waft substances across the surface of the tissue in one direction
• Ciliated epithelial cell


  A type of epithelial cell that lines the surface of structures such as the respiratory tract and uterus
• Concentration gradient


  The difference in concentration between two areas
• Denaturation


  Upon exposure to high temperatures or extremes of pH, the permanent change in the shape of an enzyme's active site that prevents the binding of a substrate
• Diffusion


  The net spreading out of particles from a high concentration to a lower concentration (down their concentration gradient)
• Diploid cell


  A cell that contains two copies of each chromosome (i.e. a full set of chromosomes)
• Egg cell


  A specialised female sex cell involved in reproduction
• Electron microscope


  A type of microscope that uses a beam of electrons, focused using magnets, to produce an image of a specimen. It has a greater magnification and resolution than a light microscope
• Emulsion test


  A chemical test that produces a cloudy emulsion when performed on lipids
• Enzyme


  A biological catalyst that increases the rate of reactions in living organisms
• Eukaryotic cell


  A type of cell found in plants and animals that contains a nucleus
• Flagella


  A long hair-like structure found on bacterial cells that is used for cell movement
• Haploid cell


  A cell that contains a single copy of each chromosome (i.e. half the number of chromosomes)
• Iodine test


  A chemical test that produces a blue/black colour when iodine solution is added to a sample containing starch
• Light microscope


  A type of microscope that uses a series of lenses to magnify the visible light reflecting off a specimen. It has a lower magnification and resolution than an electron microscope
• Lipases


  Enzymes that break down lipids into fatty acids and glycerol
• Lipid


  A large molecule that is synthesised from fatty acids and glycerol
• Lock and key hypothesis

  A theory that describes how substrates must be the correct shape to fit the active site of an enzyme
• Magnification


  The number of times bigger an image appears compared to the original object, calculated using the formula: image size = magnification × real size
• Micrometre (µm)


  A quantitative unit of length. One micrometre is equal to ×10^-6 metre
• Millimetre (mm)


  A quantitative unit of length. One millimetre is equal to ×10^-3 metre
• Mitochondria


  An organelle that is the site of respiration
• Nanometre (nm)


  A quantitative unit of length. One nanometre is equal to ×10^-9 metre
• Nucleus


  An organelle found in most eukaryotic cells that contains the genetic material of the cell and controls the activities of the cell
• Organelle


  A specialised structure found inside a cell
• Osmosis


  The diffusion of water molecules from a region of high water concentration to a region of lower water concentration across a partially permeable membrane
• Percentage change in mass

  The proportion of the mass of a substance that has changed over a set period, calculated using: (change in mass / original mass) x 100