Methods of studying cells microscopes

• Describe how to produce a scientific diagram

  No sketched or hanging or crossing lines or shading; It must look similar to the image; must be correctly labelled, without overlapping lines;

  Correct scale calculated and stated;
• Describe how do measure an object using an eyepiece graticule in an optical microscope

  Calibrate the graticule using the stage micrometer. Count the number of divisions in the graticule to measure the image. Multiply the number of divisions by the calibrated measurement of each division
• Give the magnification equation

  Magnification = size of image / size of real object
• Describe and explain how to prepare a specimen for a light microscope

  Slice the specimen very thinly (e.g. single layer of cells) so light can pass through. Add a drop of stain to the specimen to increase contrast between different cellular components. Add the coverslip ensuring there are no air bubbles.
• Give two safety precautions that must be taken when cutting specimens


  Cut onto a hard surface

  Cut away from the body
• Why do you press down lightly on the coverslip but not push it sideways

  Push down to create a monolayer of cells

  Do not push sideways as it may roll cells on top of oneanother.
• Describe the principles of a light microscope

  Light microscopes use light transmitted through the specimen to form an image. They have a maximum resolution of 0.2um (low resolution), this means they are unable to see ribosomes, ER and lysosomes. The maximum magnification is about x1500 (low magnification).
• Give the difference between magnification and resolution

  Magnification is how much bigger an image looks compared to the object. Resolution is the shortest distance between two points on a specimen that can still be distinguished as separate by the observer.
• Give the principles of a transmission electron microscope

  Transmission electron microscopes (TEM) use a beam of electrons through the specimen to form an image. Electrons don't pass as easily through denser parts.

  The image is therefore 2D. They have a high resolution of 0.1nm. The maximum magnification is about x500000. Samples need to be dead, thinly sliced and in a vacuum. The images are black and white.
• Describe the principles of a scanning electron microscope

  Scanning electron microscopes (SEM) use a beam of electrons to reflect off the specimen. The electrons are then scattered on to the reciever. The image is then built by a computer to be 3D. They have a high resolution of 0.1nm. The maximum magnification is about x100000. Samples need to be dead. The images are black and white. The images are 3d
• Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

  TEM use electrons and optical use light; TEM allows a greater resolution;

  So with TEM smaller organelles can be observed and in greater detail; TEM view only dead and optical can view live specimens; TEM does not show colour and optical (can); TEM requires thinner specimens; TEM requires a more complex and time consuming preparation; TEM focuses using magnets and optical uses glass lenses;
• An electron microscope can see more detail and smaller organelles than a light microscope

  Electron microscopes have a much higher resolution than light microscopes, so can distinguish details that are closer together.