3.1 - 3.8 Cell structure and microscopy

• Eukaryotic cells

  • have a nucleus
  • have membrane bound organelles
• Prokaryotic cells

  • normally bacteria cells
  • doesnt have a nucleus but instead a nucleoid and plasmids
  • dont have membrane bound organelles
• Cell organisation

  • Groups of cells that carry out a common function are known as a tissue
  • Groups of tissue that carry out a common function form an organ
  • Groups of organs that carry out a common function form an organ system
• Eukaryotic cells

  A) Mitochondrion

  B) Smooth endoplasmic reticulum

  C) Cytoplasm

  D) Cell membrane

  E) Ribosomes (80S)

  F) Lysosome

  G) ROugh endoplasmic reticulum

  H) Nucleolus

  I) Nucleus

  J) Golgi apparatus

  
• Nucleus

  • surrounded by a double membrane called the envelope that has pores so that molecules can enter and leave the nucleus
  • Also contains chromatin and a nucleolus which is the site of ribosome production
• Rough endoplasmic reticulum

  • a series of flattened sacs (cisternae) enclosed by a membrane with ribosomes on the surface
  • folds and processes proteins made on the ribosomes
  • makes proteins that will be secreted out or put in the cell membrane
• Smooth endoplasmic reticulum

  • system of flattened sacs (cisternae)
  • produces and processes lipids and carbohydrates
• Golgi apparatus

  • a series of fluid filled, flattened and curved sacs (cisternae) with vesicles surrounding the edges
  • processes and packages proteins and lipids
  • produces lysosomes
• Mitochondria

  • oval shaped, bound by a double membrane called the envelope
  • inner membranes fold to form cristae with a matrix on the inside containing all the enzymes needed for respiration
• Centrioles

  • hollow cylinders containing a ring of microtubules aranged at right angles to each other
  • involved in cell division
• Ribosomes

  • comprised of two subunits
  • site of protein production
• Lysosome

  • vesicle containing digestive enzymes bound by a single membrane
• Prokaryotic cell

  A) nucleoid

  B) cell membrane

  C) plasmids

  D) murein cell wall

  E) pili

  F) capsule

  G) mesosome

  H) flagellum

  I) cytoplasm

  J) ribosome

  
• Cell wall

  • rigid outer covering made of peptidoglycan / murein
• Capsule

  • protective slimy layer which helps the cell to retain moisture and adhere to surfaces
• Plasmid

  • circular piece of extra DNA
• Flagellum

  • a tail like structure which rotates to move the cell
• Pili

  • hair like structures which attach to other bacterial cells
• Mesosomes

  • infoldings on the inner membrane which contain enzymes required for respiration
• Resolution - the degree to which it is possible to distinguish between two points that are close together
• Magnification - the degree to which an image of an object is larger than the object itself
• Image size = actual size x magnification (I/AM)
• Optical microscope - uses light to form an image, light has a longer wavelength than electrons so this microscope has a lower resolution
• Advantages of optical microscope

  • easy to use
  • easy to prepare
  • can view live specimens
• Disadvantages of optical microscope

  • lowest resolution
  • lowest maximum magnification
  • only large organelles are visible
• Scanning electron microscope - A microscope that uses a beam of electrons to produce a magnified image
• Advantages of SEM

  • higher resolution than optical microscope
  • higher magnification than optical microscope
  • Forms 3D images
  • can be used on thick specimens
• Disadvantages of SEM

  • Lower resolution than TEM
  • expensive
  • large
• Transmission electron microscope - passes electrons through a thin specimen; denser regions absorb more electrons so less pass through creating a darker area on the image (black and white image)
• Advantages of a TEM

  • Highest resolution
  • Highest magnification
  • Can see internal structures of organelles
• Disadvantages of TEM

  • needs very thin specimen
  • slides are hard to prepare
  • expensive
  • large
• Staining in microscopy

  • stains and dyes are applied to tissue and bind to organelles making them easier to view
  • staining increases the contrast in the image formed, this can make it easier to see apart objects that are close together
  • increase resolution