AS Biology

• Microscope


  Device used to study cells
• Types of Microscopes


  • Light
  • Electron
• Light Microscope


  • Source of radiation: Light
  • Wavelength of radiation: 400-700nm
  • Maximum resolution: 200nm
  • Lens: Glass
  • Specimen: Alive
  • Stains: Coloured dyes
  • Image: Coloured photomicrograph
  • View: Eyepiece
• Electron Microscope


  • Source of radiation: Electrons
  • Wavelength of radiation: 0.1nm
  • Maximum resolution: 0.5nm TEM, 1nm SEM
  • 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 an RT vacuum, so the specimen should be dead
• Magnification


  The number of times larger an image is compared to the object's size

  
• 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


  The 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 the specimen
• Electrons have extremely short wavelengths. They are negatively charged, thus easily focused using electromagnets
• Electron micrograph


  Very small particles can be observed as the electrons are easily absorbed. The parts of the specimen that appear darker in the final image are denser and absorb more electrons
• Ultrastructure


  The structure revealed by the electron micrograph
• Organelles


  Functionally and structurally distinct part of a cell, usually membrane bound

  
• Animal Cell


  • Cell surface membrane: selectively permeable membrane that allows for the exchange of certain biological molecules and ions
  • Nucleus: largest organelle surrounded by the double membraned nuclear envelope and is continuous with rough endoplasmic reticulum
  • Rough endoplasmic reticulum: an extensive membrane system with 80S ribosomes are sites for protein synthesis
  • Smooth Endoplasmic reticulum: site for lipid synthesis and steroids
  • Golgi body/complex/apparatus: stack of flattened membranes enclosing hollow sacs (cisternae) formed by transport vesicles
  • Mitochondria: surrounded by mitochondrial envelope; provides energy for aerobic respiration, synthesizes lipids
  • Ribosomes: the site at which mRNA is translated into polypeptides
  • Lysosomes: contain digestive (hydrolytic) enzymes
  • Microtubules: long hollow tubes that make up the cytoskeleton which helps determine cell shape
  • Centrosome: pair of centrioles at right angles that's involved in nuclear division and act as MTOCs

  
• Plant Cell


  • Cell wall: rigid as it contains cellulose fibres
  • Plasmodesmata: pore-like structures found in cell walls that allow a link between neighbouring cells
  • Large vacuole and tonoplast: surrounded by partially permeable tonoplast, has cell sap (fluid) that consists of enzymes, sugars, waste products, pigments, mineral salts, oxygen, and C02 and regulates osmotic properties
  • Chloroplasts: This cell structure is only found in plant cells and carries out photosynthesis and ATP synthesis

  
• Eukaryotes


  Organisms with a true nucleus and have membrane-bound organelles

  
• Prokaryotes


  Organisms that lack a nucleus and have simpler structures
• Comparison of Eukaryotes and Prokaryotes

  • Average Diameter of Cell
  • DNA
  • Ribosome
  • ER
  • Organelles
  • Cell Wall
  • Cell division
  • Transcription and translation

  
• Viruses


  Non-cellular and are parasitic as they reproduce by infecting and taking over living cells
• Glucose


  An energy source which is broken down during respiration. It is also the monomer from which Starch and Cellulose are made
• Monomer


  A simple molecule that is used as a basic building block for the synthesis of a polymer
• Polymer


  A giant molecule made from monomers
• Macromolecules


  Large and complex molecules that are formed due to the polymerisation of smaller monomers
• Monosaccharide


  A molecule consisting of a single sugar unit, the simplest form of carbohydrate
• Starch test


  Iodine turns blue-black quickly.
• Glucose


  Molecular formula C6H12O6, an energy source broken down during respiration, monomer for starch and cellulose
• α-glucose and β-glucose


  Differ in the position of an -OH group in their ring structures
• Monomer


  Simple molecule used as a basic building block for the synthesis of a polymer
• Polymer


  Giant molecule made from monomers
• Macromolecule


  Large and complex molecules formed due to the polymerisation of smaller monomers
• Monosaccharide


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


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


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


  Covalent bond between constituent monomers formed due to a condensation reaction
• Hydrolysis


  Can separate constituent molecules by breaking the glycosidic bond between monomers
• Starch


  Macromolecule found in plant cells, made up of amylose and amylopectin, polysaccharides with 1,4 glycosidic bonds, compact and stores energy
• Starch components


  • Amylose
  • Amylopectin
• Amylose


  • Has α 1,4 glycosidic bonds, helical and more compact
• Amylopectin


  • Has α 1,4 and α 1,6 glycosidic bonds, giving it's branched structure