TOPIC 2

• Speed of light (optical) microscope

  Fast
• Cost of light (optical) microscope

  Cheap
• Specimens for light (optical) microscope  

  Alive or Dead, but must be thin
• Image produced from light (optical) microscope  

  2D and can be in colour if stains used
• Resolution of light (optical) microscope 

  200nm 
• Magnification of light (optical) microscope 


  X1,500 
• What can a light (optical) microscope be used to see? 

  Whole cells and tissues (no small organelles) Optical microscopes have a maximum resolution of around 0.2 micrometres (µm) or 200 nm

  • Therefore optical microscopes can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts
  • Optical microscopes cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosomes
• Cost of laser scanning confocal microscope 

  Expensive 
• Speed of laser scanning confocal microscope 

  Time consuming  
• Specimens for laser scanning confocal microscope 


  Alive or Dead and thin or thick 
• Image produced from laser scanning confocal microscope  

  2D or 3D and can be in colour if fluorescent tags used
• Resolution of laser scanning confocal microscope 

  800nm 
• Magnification of laser scanning confocal microscope 

  X17,820 
• What can a laser scanning confocal microscope be used to see? 

  Organelles and can even see cytoskeleton Multiple depths of the tissue section/organisms are scanned to produce an image

  • Think of it like the laser beam is building up the image layer by layer
• Cost of transmission electron microscope  

  Expensive 
• Speed of transmission electron microscope   

  Time consuming
• Specimens for transmission electron microscope  

  Dead and thin
• Image produced from transmission electron microscope  

  2D and black and white
• Resolution of transmission electron microscope 

  0.5nm 
• Magnification of transmission electron microscope   

  X500,000
• What can a transmission electron microscope be used to see?  

  the internal structures within cells (or even within organelles) to be seen
• Cost of scanning electron microscope  


  Expensive 
• Speed of scanning electron microscope    

  Time consuming
• Specimens for scanning electron microscope  

  Dead and thin or thick
• Image produced from scanning electron microscope 

  3D and black and white 
• Resolution of scanning electron microscope 

  5nm 
• Magnification of scanning electron microscope  

  X100,000 
• What can a scanning electron microscope be used to see? 

  They allow the external, 3-D structure of specimens to be observed 
• The use of staining in light microscopy

  Differential staining = to give the sample colour and contrast in order to distinguish between two types of organisms that would otherwise be hard to identify. it can also differentiate between different organelles of a single organism within a tissue sample.
• Preparing a dry mount slide


  Solid samples like hair and pollen can be viewed whole and muscle tissues/plants can be sectioned with a sharp blade. Next the specimen is placed in the center of the slide with a cover slip placed over it.
• Preparing a wet mount slide

  Specimen is suspended in a liquid like water or an immersion oil and a cover slip placed over it eg. Aquatic samples
• Preparing a squash slide


  wet mount first prepared then a lense tissue gently pressed down the cover slip or a second slide can be used depending on the sample to avoid the cover slip being damaged eg. Root tip to see cell division.
• preparing smear slides


  the edge of a slide is used to create a thin even coating on a slide eg. Blood
• Why are images of cells often low contrast

  As most cells don’t absorb light so a stain is often added
• Magnification Vs Resolution 


  Magnification = is the ability to make small objects seem larger such as making a microscopic organisms visible. Resolution = the ability to distinguish two objects from each other.
• Function of nucleus 


  Stores genetic material
• Structure of nucleus 


  Nuclear envelop, nuclear pores and nucleolus
• Function of nucleolus 


  To produce and assemble the cells ribosomes
• Structure of nucleolus


  Spherical ball inside nucleolus composed of proteins and RNA which from ribosomes
• function of nuclear envelope 


  Provides barrier between cytoplasm and nuclear contents and gives nucleus sturdy structure and shap.