Cell biology

• Light microscopes


  Microscopes that use light to magnify biological specimens
• Cell sizes


  • Animal cells: 0.01 mm - 0.05 mm
  • Plant cells: 0.01 mm - 0.10 mm
• The human eye can see objects as small as around 0.05 mm. A microscope is required to see cells in any detail.
• Microscope


  Magnifies the image of a biological specimen so that it appears larger
• Compound microscope


  The type of microscope used in a school laboratory
• Calculating the magnification of the microscope

  Magnification of the microscope = magnification of eyepiece × magnification of objective
• Most animal and plant cells are 0.01 – 0.10 mm in size. The smallest thing seen with the naked eye is about 0.05 mm.
• For all cells we need a microscope to see them in any detail.
• Micrometre (μm)


  The best unit to measure most cells
• Nanometre (nm)


  The best unit to measure sub-cellular structures and viruses
• Division of a metre

  • Millimetre, mm
  • Micrometre, μm
  • Nanometre, nm
• Standard form


  Shows the size of numbers as powers of ten
• Preparing biological samples for examination

  1. Stain cells

  2. Examine a range of cells and structures

  3. Place coverslip over specimen
• When viewing any slide with a microscope, a small square or circle of thin glass called a coverslip is placed over the specimen. It protects the microscope and prevents the slide from drying out when it's being examined.
• Most cells are colourless. Stains are used to add contrast. Certain stains are also used to stain specific cell structures or cell products.
• Investigating cells with a light microscope

  1. Examine animal or plant cells

  2. Make observations and draw scale diagrams of cells
• Low power diagram


  Used to show the arrangement of distinct regions of the tissue or the outline of individual cells that make up a uniform tissue
• High power diagram


  A detailed image of a part of the slide, usually showing a single cell
• Development of light microscopes

  1. 1590s - Dutch spectacle makers Janssen experimented with putting lenses in tubes, made the first compound microscope

  2. 1650 - Robert Hooke observed and drew cells using a compound microscope
• Resolution


  The ability to see two points as two points, rather than merged into one
• The resolution of a light microscope is around 0.2 μm, or 200 nm. This means that it cannot distinguish two points closer than 200 nm.
• Electron microscope


  Uses a beam of electrons instead of light rays
• Types of electron microscope

  • Scanning electron microscope (SEM)
  • Transmission electron microscope (TEM)
• The TEM has revealed structures in cells that are not visible with the light microscope.
• Animal cells


  • Have a basic structure
  • Mitochondria are visible with the light microscope but can't be seen in detail
  • Ribosomes are only visible with the electron microscope
• Cell structures and their functions

  • Cytoplasm
  • Nucleus
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Cell structures and their functions (plant cells)

  • Chloroplast
  • Cell wall
  • Permanent vacuole
• Differences between eukaryotic and prokaryotic cells

  • Size
  • Outer layers of cell
  • Cell contents
  • Genetic material
  • Type of cell division
• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes


  Cells that lack a nucleus and membrane-bound organelles
• Components of animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Organelles


  Structures in a cell that have different functions
• Orders of magnitude


  Used to understand how much bigger or smaller one object is from another
• Prefixes


  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Structures only in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells

  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• Cell specialisation


  The process where cells gain new sub-cellular structures to be suited to their role
• Specialised animal cells


  • Sperm cells
  • Nerve cells
  • Muscle cells