Core knowledge

• Chemical elements


  Joined together to form biological compounds
• Water


  • A polar molecule which allows hydrogen bonds between molecules giving unique important properties
• Important properties of water

  • Solvent
  • Metabolite
  • High specific heat capacity
• Functions of water


  • Polar molecules dissolve in water and are able to be transported
  • Water is a reactant in photosynthesis and hydrolysis, produced in aerobic respiration and condensation
  • A lot of energy is required to change the temperature of water so aquatic environments remain stable
  • High latent heat of evaporative cooling
• Water


  • Surface tension
  • Support and Buoyancy
• Monosaccharides


  • 3C important in respiration and photosynthesis
  • 5C important in nucleotides
  • 6C Glucose is a really important hexose sugar. It is used in respiration
• Monosaccharides


  Linked to make disaccharides and polymers
• There are two isomers of glucose
• Proteins


  Constructed from 20 types of amino acid
• Amino acid


  The general form is shown here
• Two amino acids can form a dipeptide. A polymer is called a polypeptide
• Primary structure of proteins

  • The sequence of amino acids as coded by the DNA
• Secondary structure of proteins

  • Hydrogen bonds formed between the amino acids in the chain cause it to fold into an alpha helix or beta pleated sheet
• Tertiary structure of proteins

  • Hydrophobic interactions between the variable groups within the secondary structure, and disulphide and ionic bonds, form a very specific folded structure e.g. the active site of an enzyme
• Quaternary structure of proteins

  • More than one polypeptide chain linked to form a molecule
  • Fibrous proteins have a structural function
  • Globular proteins have a metabolic function
• Test for proteins


  1. Add Biuret solution

  2. Positive reaction - A purple/violet colour is seen
• Disaccharides


  • Glucose and fructose linked in a condensation reaction where one molecule of water is lost and a glycosidic bond is formed
  • Glucose and α-glucose
  • Glucose and galactose
• Polysaccharides


  • A polymer of α-glucose (composed of straight chain amylose and branched amylopectin)
  • Compact energy storage in plants with the osmotic effect
  • Glycogen - A polymer of α-glucose, energy storage in animals
  • Cellulose - A polymer of β-glucose, adjacent monomers twisted through 100° to each other, allowing hydrogen bonds between chains, forming microfibrils - A strong structure for plant cell walls
  • Chitin - As cellulose but with some -OH groups replaced by nitrogen-containing acetylamine groups - Strong, weight and waterproof for skeletons
• Test for starch


  1. Add iodine solution

  2. Positive reaction - A blue/black colour is seen
• Test for reducing sugars

  1. Add Benedict's reagent

  2. Positive reaction - A semi-quantitative test, the further along the colour spectrum the solution goes the more sugar is present

  3. For non-reducing sugars, they must be hydrolysed by boiling in hydrochloric acid first
• Inorganic ions


  • Anion that contains no more than one carbon atom
• Lipids


  Functions include insulation, energy storage and protection
• Triglyceride


  Glycerol linked to 3 fatty acid chains during condensation reactions forming ester bonds
• Phospholipid


  Glycerol linked to 2 fatty acid chains and a phosphate molecule. Has a hydrophilic head and hydrophobic tail. These properties explain the plasma membrane lipid bilayer
• Test for lipids


  1. Mix with absolute ethanol then add an equal volume of water

  2. Positive result - A cloudy emulsion is formed
• Fatty acids


  • Unsaturated - Mono-unsaturated have one carbon-to-carbon double bond, poly-unsaturated have two or more
  • Saturated - Have only single carbon-to-carbon bonds
  • A high intake of saturated fats is a contributory factor in heart disease as it raises the low-density lipoprotein (LDL) cholesterol level, which increases the incidence of atheroma in coronary arteries
• Viruses are too small to be seen under a light microscope
• A light microscope can be used to view eukaryotic and prokaryotic cells
• Cell


  The basic unit of life
• Tissue


  A group of cells with the same structure and function working together
• Organ


  A structure made up of different tissues working together
• Organism


  A living thing
• Bacteria are prokaryotic cells. They contain no membrane-bound organelles
• Viruses contain DNA or RNA and a protein coat, but do not have cytoplasm or organelles
• Light microscope


  • Can magnify up to 2000x, but those in schools are likely to have a maximum magnification of 400 or 1000x
• Electron microscope


  • Has a much higher magnification of over 100,000x and better resolution
• Calibrating a microscope


  Line up the smaller eyepiece graticule and larger stage micrometer

  2. Count how many eyepiece units fit into the stage units

  3. The size of each stage micrometer unit is known

  4. Calculate the size of each eyepiece unit

  5. Convert the eyepiece unit size from mm to μm

  6. Remove the stage micrometer and replace with the specimen slide

  7. Draw the specimen, using clear lines, no shading, and label structures clearly
• Fluid mosaic model


  Proposed by Singer and Nicholson in 1972 for the structure of the cell membrane

  Fluid - the phospholipid molecules within a layer can move relative to each other

  Mosaic - the proteins within the phospholipid layer are of different sizes and shapes and form different patterns
• Cell membrane permeability


  • Selectively permeable - only allows certain molecules through

  Permeability increased by: temperature increases above 40°C, organic solvents dissolving phospholipids

  Lipid soluble substances and small molecules can dissolve and move directly through the phospholipid bilayer

  Water soluble substances must use intrinsic proteins to pass through
• Phospholipid bilayer


  The hydrophilic phosphate heads form the outer and inner surface, the hydrophobic fatty acid tails point towards each other