as level biology theory

• Microscopy


  The study of cells and their components using microscopes

  
• Types of microscopes


  • Light
  • Electron
• Light microscope


  • Source of radiation: Light
  • Wavelength of radiation: 400-700nm
  • Max resolution: 200nm
  • Lens: Glass
  • Specimen: Alive
  • Stains: Coloured dyes
  • Image: Coloured photomicrograph
  • View: Eye piece
• Electron microscope


  • Source of radiation: Electrons
  • Wavelength of radiation: ±0.005nm
  • Max resolution: 0.1-0.5nm
  • Lens: Electromagnet
  • Specimen: Dead
  • Stains: Heavy metal
  • Image: Black and white electron micrograph
  • View: Fluorescent screen
• Vacuum present in EM to prevent electrons from colliding with air particles to gain a sharp image
• Water boils in RT in a vacuum, so specimen should be dead
• Magnification


  Number of times larger an image is compared to the real size of the object
• Calculating magnification


  1. Eyepiece graticule: fitted into the eyepiece of the microscope and is used to measure objects

  2. Stage micrometer: has an accurate scale (in mm) and provides reference dimensions

  3. 1mm= 1000 μm

  4. 1μm= 1000 nm

  5. Use the same magnification when calibrating the eyepiece graticule and when using it to measure the specimen
• Resolution


  Ability to distinguish between two separate points. The amount of detail that can be seen- higher resolution, higher detail
• Limit of resolution


  Half the wavelength of radiation used to view specimen
• Electrons have extremely short wavelength and are negatively charged, thus easily focused using electromagnets
• Ultrastructure


  The structure revealed by the electron micrograph
• Organelles


  Functionally and structurally distinct part of a cell, usually membrane bound
• what is the cell surface membrane?

  • selectively permeable, phospholipid bilayer
• Plant cell


  • Cell wall: rigid, contains cellulose fibres
  • Chloroplasts: site of photosynthesis
  • Large vacuole: regulates osmotic properties
  • Plasmodesmata: pore-like structures in cell walls that allow communication between cells

  
• Eukaryote


  Organisms with a true nucleus and membrane bound organelles
• Prokaryote


  Organisms that lack a nucleus and have simpler structure
• Comparison of eukaryotes and prokaryotes

  • Cell size
  • DNA structure
  • Ribosome size
  • Endoplasmic reticulum
  • Organelles
  • Cell wall composition
  • Cell division
• Viruses


  Non-cellular, parasitic, reproduce by infecting and taking over living cells
• Biological molecules


  Macromolecules formed from monomers
• Benedict's test for reducing sugars


  1. Mix equal volume of sample and Benedict's solution, heat in water bath up to 95C

  2. Positive: green → yellow → orange → brick red

  3. Negative: blue
• Benedict's test for non-reducing sugars

  Acid or enzyme hydrolysis to break down non-reducing sugars, then Benedict's test
• Biuret's test for proteins

  1. Mix equal amounts of sample and Biuret's solution

  2. Purple colour indicates presence of proteins, blue indicates absence
• Emulsion test for lipids

  1. Dissolve sample in ethanol, then add water

  2. Milky white emulsion indicates presence of lipids
• Iodine test for starch

  1. Add iodine solution to liquid being tested

  2. Blue-black colour indicates presence of starch
• Glucose


  Monosaccharide, energy source, broken down in respiration, monomers for starch and cellulose
• Monomer


  Simple molecule used as building block for polymers
• Polymer


  Giant molecule made from monomers
• Macromolecule


  Large and complex molecules formed by polymerisation of smaller monomers
• Monosaccharide


  Molecule consisting of a single sugar unit, simplest form of carbohydrate
• Disaccharide


  Sugar molecule consisting of two monosaccharides joined by a glycosidic bond
• Polysaccharide


  Polymer whose subunits are monosaccharides joined by glycosidic bonds
• Glycosidic bond


  Covalent bond between constituent monomers in polysaccharides and disaccharides, formed by condensation reaction
• Starch


  • Macromolecule found in plant cells, made of amylose and amylopectin (both polysaccharides of glucose)
  • Amylose: α 1,4 glycosidic bonds, helical and compact
  • Amylopectin: α 1,4 and α 1,6 glycosidic bonds, branched

  
• Glycogen


  • Macromolecule for energy storage in animal cells, similar structure to amylopectin but more branched
• Cellulose


  • Found in plant cell walls, made of β-glucose units with β-1,4 glycosidic bonds, hydrogen bonding between parallel molecules
• Triglyceride


  Formed by condensation of 3 fatty acid chains and a glycerol molecule, forming ester bonds

  
• Glycogen


  • Macromolecule used for energy storage in animal cells
  • Made from α glucose molecules
  • Structure similar to amylopectin but more branched and contains more α 1,6 glycosidic bonds
• Cellulose


  • Found in plant cell walls
  • Made from β-glucose units that form β-1,4 glycosidic bonds
  • Alternate β-glucose molecules are rotated 180 degrees
  • Hydrogen bonds form between parallel cellulose molecules
  • 60-70 cellulose molecules form bundles called microfibrils
  • Microfibrils are held together in bundles called fibres by hydrogen bonding
• Fibres


  • Increase tensile strength to withstand osmotic pressure, making the plant rigid and determining cell shape
  • Freely permeable