Methods of Studying Cells

• What is magnification?

  Making an image larger than the object
• Magnification is when an image is made larger than the object, when using a microscope, we can increase the magnification by using a higher powered objective lens, this allows us to see in more detail because it increases the size of the image of small details.
• How do we increase the magnification on the microscope?

  Using a higher powered objective lens
• Increasing the magnification allows us to see in more detail because it increases the size of the image of small details
• Magnification = size of image / size of real object
• What is the magnification calculation?


  Size of the image / size of real object
• How would we calculate size of image (magnification)?

  Magnification x size of real object
• How would we calculate the real size of an object (magnification)?

  Size of image / magnification
• Resolution is the ability to distinguish between two objects at separate points
• What is resolution?


  The ability to distinguish between two objects at separate points
• The higher the resolution, the better the clarity and detail of the image
• What happens when resolution increases?


  The clarity and detail of the image increases
• What are the two types of microscopes?

  Optical and electron
• What are the most common microscopes used by biologists?

  Light microscopes
• Why are light microscopes commonly used?

  They are relatively cheap, easy to use and can magnify living cells or small organisms so their activity and behaviour can be studied
• How do light microscopes produce an image?


  Visible light passes and is bent through the lens system to enable the user to see the specimen, which can be alive
• Individual cells are generally transparent and their components are not distinguishable unless they are coloured with special stains, however these stains usually kill the cells
• Why are stains used in light microscopes?

  Individual cells are usually transparent and their components are not distinguishable otherwise
• What is the disadvantage of using stains?

  They usually kill the cells
• Using light limits the resolution of optical microscopes as, using light, it is impossible to distinguish between two objects that are closer than half the wavelength of light.
• What is the wavelength of light?

  500-600 nm
• Light microscopes use a beam of light to form larger and more detailed images
• Light microscopes can magnify up to 1500x but only have a maximum resolution of 0.2 micrometers.
• Using a light microscope at the highest magnification and resolution, the mitochondria can only just be seen and other organelles such as ribosomes, lysosomes and the ER are too small to be seen.
• Light microscopes can be used to view living cells and organisms, but they must be thin and often require staining
• Electron microscopes use electrons instead of light to produce an image
• The electron microscope uses a beam of electrons which pass through the specimen and hit a screen or photographic plate on the other side. The intensity of the beam hitting the screen/plate depends on how many electrons were absorbed by the specimen. This produces a black and white image with high contrast.
• Electron microscopes helped us to see smaller organelles such as ribosomes, something the light microscope cannot magnify because they are too small
• Electron microscopes allow us to see the details inside organelles like mitochondria, which furthered our understanding of sub-cellular structures
• Electron microscopes have a higher magnification and resolution than light microscopes
• Electron microscopes use a beam of electrons to produce an image and can magnify up to 1,500,000 times.
• What is a disadvantage of electron microscopes?

  They are large, very expensive and cannot use live specimens
• Images produced by electron microscopes are often in 3D
• Electron microscopes have a resolution of around 0.1nm, this is around 1000x more than light microscopes
• Having a resolution of 0.1nm means that electron microscopes can clearly distinguish two points that are 0.1nm apart as separate objects.
• Electron microscopes have a higher resolution as they use a beam of electrons to produce an image instead of light, and their wavelength is smaller
• What are the two types of electron microscopes?

  Transmission and Scanning
• Transmission electron microscopes work by shooting a beam of electrons (focused using electromagnets) at a thin slice of a sample and detecting those electrons that make it through the other side.
• How does a transmission electron microscope produce an image?

  The electron beam penetrates the cell and provides details of a cells internal structure, the denser parts of the specimen absorb more electrons, which makes these denser parts appear darker on the final image produced, providing contrast between the different structures.
• The TEM allows us to look in very high resolution at a thin section of a sample, making it particularly good for learning about how components inside a cell, such as organelles are structured internally