Microscopes

• • Purpose of a Microscope: It enables us to see specimen that are too small to be seen with the naked eye.
• • Define specimen– is the object/ material observed under the microscope
• • Define magnify: make tiny specimen appear big
• • Define Resolve: ability to differentiate between two or more things that normally appear as one when seen with the naked eye.
• • State the 2 types of microscope
  • Optical Microscope
  • Electron Microscope
• • What does optical microscope use to observe the specimen? uses light
• • What type of image does dissection microscope produce? 3D image
• • Another name of dissection microscope.: Stereo Microscope
• The light microscope is used to observe cells, tissues, organs, and organisms.
• • List the 3 types of optical microscope(i) Simple Microscope (one lens) (ii) Compound Microscope (many lenses) (iii) Dissection/Stereo Microscope (3D image)
• • Commonly used microscopes in schools and universities are? optical microscopes
• • What does electron microscope use to observe the specimen? uses electrons
• • State the four types of electron microscopes
  • Transmission Electron Microscope (TEM)
  • Scanning Electron Microscope (SEM)
  • Scanning Transmission Electron Microscope (STEM)
  • Reflection Electron Microscope (REM)
• • What was the first type of electron microscope?Transmission Electron Microscope (TEM)
• • Define transmission electron microscope (TEM)High voltage electron beam emitted by a cathode and formed by magnetic lenses
• • What type of specimen is required for the transmission electron microscope? Ultra-thin specimen required to allow the electrons to pass through.
• • What type of image is produced in transmission electron microscope (TEM)? Image produced is 2D black and white image.
• • State the main difference between Transmission electron microscope and Scanning electron microscope .In TEM, the electrons in the primary beam are transmitted through the specimen but in the Scanning Electron Microscope (SEM) images are produced from the secondary electrons which are emitted from the surface due to excitation by the primary electron beam.
• • How does the SEM work exactly? The electron beam is scanned across the surface of the sample in a raster pattern, with detectors building up an image by mapping the detected signals with beam position.
• • Define Scanning transmission electron microscopeSTEM combines the capabilities of both an SEM and a TEM.  The electron beam is transmitted across the sample to create an image (TEM) while it also scans a small region on the sample (SEM).
• • How does Reflection electron microscope work? Uses scattered high-energy electrons falling on a surface at glancing angles to generate an image of the surface.
• • State the two magnification characteristics of REM. This type of microscope usually has two magnification characteristics: magnification in the electron beam incidence plane and magnification in the plane perpendicular to the incidence plane
• • List the 13 parts of a Compound Microscope
  • Ocular Lens (Eyepiece)
  • Objective Lens
  • Arm
  • Stage
  • Stage Control
  • Coarse Adjustment
  • Fine Adjustment-
  • Light Switch
  • Base
  • Brightness Control
  • Light Source
  • Condenser
  • Nosepiece
• • State the function of ocular lens. Lens through which specimen is viewed. Magnifies specimen
• • What is another name of ocular lens? Eyepiece
• • Function of objective lens. Lens close to the specimen; magnifies the specimen together with ocular lens
• • Function of arm. Connects the body tube to the base of the microscope; for holding microscope.
• • Function of stage. platform where specimen is placed
• • Function of stage control. moves the stage sideways, right and left.
• • Function of coarse adjustment. brings the specimen into focus by moving the tube or stage up/down bigger distance in respect to the slide.
• • Function of fine adjustment. Fine tunes the focus and increases the detail of the specimen
• • Function of light switch. switches the light on/off.
• • Function of base. The base supports the microscope and it’s where the light is located.
• • Function of brightness control. allows the user to control the amount of light produced by the Light Source.
• • Function of light source. provides light.
• • Function of condenser. Gathers and focuses light from the illuminator onto the specimen being viewed
• • Function of nosepiece. Rotates to allow the viewer to select different objective lenses.
• • List the four steps for preparing wet mounts

  1. On a clean slide place a drop of water or the required stain.
  2. In that drop, place the specimen. (Place a thin slice of the specimen if it is too big)
  3. Lower a cover-slip at an angle of 45º to avoid trapping of air bubbles. Note: If there is excess water in the wet mount, place a piece of tissue paper near the edge of the cover-slip for it to draw and absorb water. If there is too little water; using a dropper add some more water near the edge of the cover-slip.
  4. Observe the wet mount under the microscope.
• • what is needed for specimens to be observed under 100X objective lens? Specimens to be observed under 100X objective lens requires oil of immersion
• • Write the formula for calculation of Total magnification 𝐓𝐨𝐭𝐚𝐥 𝐌𝐚𝐠𝐧𝐢𝐟𝐢𝐜𝐚𝐭𝐢𝐨𝐧: 𝐄𝐲𝐞𝐩𝐢𝐞𝐜𝐞 𝐋𝐞𝐧𝐬 × 𝐎𝐛𝐣𝐞𝐜𝐭𝐢𝐯𝐞 𝐋𝐞𝐧