Reproduction unit 2

• Cells are the basic units of all living organisms
• Organisms can be unicellular or multicellular
• New cells form by the division of existing cells
• Cells are too small to be seen by the naked eye, therefore microscopes are used to magnify
• Light Microscopes


  Uses light to shine through the specimen, then refracts through glass lenses. An image is projected onto the eyepiece
• Light Microscopes


  • Cheap, therefore commonly available in schools
  • Quick observation of cells
  • Preservation and staining of slides could cause artefacts
  • Much lower magnification and resolution compared to electron microscopes
• Electron Microscopes


  Uses beams of electrons to create an image. Electromagnetic lenses form an image. An image is projected onto a fluorescent screen
• Electron Microscopes


  • Due to the electron's low wavelength compared to visible light, high magnification and resolution can be achieved
  • Specimens are required to be in a vacuum, to prevent disturbance of electrons
  • Water boils in a vacuum, so specimen should be dead
  • Extremely expensive to buy and maintain
  • Specimens must undergo lengthy preparation before use
• Transmission Electron Microscope (TEM)

  Forms two-dimensional images
• Scanning Electron Microscope (SEM)

  Forms three-dimensional images at the compromise of a lower magnification
• 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: The ability to distinguish between two separate points. The higher the resolution, the higher the detail
• Electrons have an extremely short wavelength. This is the main reason why electron microscopes have a higher resolution
• Stains


  Coloured dye used to make viewing cell/organelles easier
• Examples of stains


  • Acetocarmine: Stains the chromosomes during cell division
  • Iodine: Stains starch-containing organelles in plants
• Cell Organization Order


  • Organelle
  • Cell
  • Tissue
  • Organ
  • Organ System
• Organelle


  A specialized part of a cell that has its own function
• Cell


  The smallest part of a living structure that can operate as an independent unit
• Tissue


  A group of cells with similar structures, working together to perform a shared function
• Organ


  A structure made up of a group of tissues, working together to perform specific functions
• Organ System


  A group of organs with related functions, working together to perform body functions
• Types of epithelial cells

  • Squamous
  • Cuboidal
  • Columnar
  • Glandular
  • Stratified

  
• Squamous epithelial cells


  Simple, flattened, epithelial cells used to cover surfaces, allowing some substances to pass through
• Cuboidal epithelial cells


  Simple cuboid shaped epithelial cells used in absorption and secretion
• Columnar epithelial cells


  A simple, columnar epithelial cell which is able to specialize
• Glandular epithelial cells


  A specialized version of columnar cells that secretes chemical substances
• Stratified epithelial cells


  Made up of multiple layers of cells, with the purpose of fast replication
• Eukaryotic cells are mainly present in animals, plants, and fungi
• Ultrastructure


  The structure revealed by the electron micrograph

  
• Main features of Eukaryotic cells


  • Nucleus
  • Nuclear pore
  • Nucleolus
  • Ribosomes
  • Rough endoplasmic reticulum
  • Smooth Endoplasmic reticulum
  • Mitochondria
  • Centrioles
  • Lysosomes
  • Golgi Apparatus
• Nucleus


  The largest organelle in the cell. It's surrounded by a double membraned nuclear envelope. It is connected to rough endoplasmic reticulum

  
• Nuclear pore


  Gaps in the nuclear envelope that allow exchange between the nucleus and cytoplasm
• Nucleolus


  A dense region of pure DNA and protein, functioning to make ribosomes
• Ribosomes


  The site at which mRNA (transcribed from the nucleus) is translated into polypeptides with the help of tRNA, therefore help with protein synthesis. They are not membrane-bound
• 70S ribosomes


  Smaller ribosomes present mostly in Prokaryotic cells
• 80S ribosomes


  Larger ribosomes present in Eukaryotic cells
• Rough endoplasmic reticulum


  An extensive membrane system with 80S ribosomes attached which produces the rough appearance. The RER provides a pathway for the transport of materials throughout a cell
• Smooth Endoplasmic reticulum


  A site for lipid and steroid synthesis
• Mitochondria


  Provides energy for aerobic respiration and is more in areas that require high energy