INS 2007-08 Pre-lab I Questions Note: You will benefit the most by reading through the laboratory handouts first before attempting to answer these questions without the help of the handouts. After you answer the questions, go back to the handouts to find the answers and correct your work. Use your pre-lab questions as a mock quiz! Open-ended questions are not meant to have one specific answer. 1) Label the parts of the compound light microscope in the diagram below (13 parts in total). 2) What is the total magnification of your specimen with the 40X objective in place? 3) What are the lowest and highest magnification capabilities of your microscope? 4) What can you say about the relationship between magnification and field of view? 5) Why is acridine orange mutagenic? 6) What is the purpose of mitosis? 7) How does mitosis differ from cytokinesis? 8) Design a feasible experiment to estimate the proportion of time that cells in actively dividing tissues, such as the root tip, actually spend in M-phase, cytokinesis, and Interphase.Introduction to Natural Science Biology Lab 1 - Microscopy and Introduction to Mitosis I. Lab Orientation It is very important to know your way around the laboratory and be able to find any equipment that you may need. During the first half hour we will help orient you to the lab. II. Microscopy Part A – Learning how to use a compound microscope The discovery of the cell and its organelles was enabled by the development and refinement of the microscope. There are two basic types of microscopes: light microscopes and electron microscopes. The light microscope uses glass lenses and visible light to form a magnified image of an object. An electron microscope uses magnets to focus an electron beam. Since we cannot see electrons, the electron microscope directs them at a fluorescent screen or photographic film to create a visible image. The light microscope is a standard instrument in the biology laboratory. The images that we see can be described graphically (by drawing and photography), qualitatively (describing shape, color, and movement), and quantitatively (measuring the number and dimensions of individual structures). Throughout the program we will emphasize the importance of being quantitative when making observations. In this lab, as you change the magnification of the image, you should pay particular attention to scale (characterizing an object as being “small” and “large” is relative, and not very informative in absolute terms). Goals 1) Identify the parts of the compound microscope and be proficient in their correct use. 2) Determine the diameter of the field of view and use it to estimate the size of the specimen 3) Understand relative sizes of different cell types 4) Familiarize yourself with the location and function of the optical and mechanical parts of the compound and microscope 5) Learn the proper technique for preparing a wet-mount slide The Compound Light Microscope The compound microscope is used to magnify and resolve fine detail within a transparent specimen (one through which light can pass). It has two separate lens systems (hence the term compound). The objective lens is located near the specimen and magnifies the image to a certain degree (4X, 10X, 40X, 100X). The ocular lens is located in the eyepiece and further magnifies the image formed by the objective lens system (10X). The total magnification of the image seen by the observer is the product of the magnification of the two lens systems (objective X ocular). The resolving power of the microscope is equally as important as its ability to magnify. Resolving power is the minimum distance two points can be separated and still be distinguished as two separate points. The resolution of a light microscope is limited by the wavelength of visible light. The maximum possible resolution of the light microscope is 0.2 µm; the highest magnification in a light microscope with maximum resolution is approximately 1000X. Observe the following precautions when using the microscope: Always carry the microscope in an upright position. Use one hand to grasp the arm (m in diagram below) of the microscope; use the other to support the base (l in diagram below). The eyepiece (ocular lens) slides into the body tube and could fall out if the microscope is tilted. Never place the microscope close to the edge of the lab table or counter. Be sure to place the electrical cord out of the way and not in a position where it could catch and drag the microscope to the floor.fgmkijedhbcalUse only lens paper or a Q-tip soaked with lens cleaner for cleaning the lenses. Using tissue paper, other materials, or a dry Q-tip could damage the lenses. Never put a microscope away with the high power objective in the viewing position or with a slide on the stage. When you are finished with your observations, remove the slide, turn off the illuminator, clean the lens, rotate the low-power objective into viewing position and make sure the stage is clean. Parts of the microscope a. Light source. The light source is built into the base with a lens that focuses light onto the lower condenser lens and is covered by an adjustable field diaphragm. b. Condenser. The condenser contains a system of lenses that focuses light on the specimen. c. Iris diaphragm. The iris diaphragm is used to adjust the amount of light striking the object. It can be opened or closed using the lever on the side of the condenser. d. Objective lenses. The objectives are mounted on a revolving nosepiece or turret (e) and each contains a complex lens system. Most new microscopes are parfocal. (Once you have focused on an object using one objective lens -usually the low power- you can then switch to high power without completely losing focus.) e. The nosepiece holds the following objectives (the magnification is indicated on the side of the objective): 4X magnification (low power objective), 10X magnification (low power objective), 40X magnification (high power objective), 100X magnification (oil immersion objective) f. Ocular Lens or Eyepiece. The ocular lens is the lens that you look through. It will usually magnify the image 10X. Focus each ocular and use both eyes to look at your specimen. One of the oculars contains a scale within the eyepiece (ocular micrometer) that you will use to make measurements. Some models are fitted with a movable body tube or head piece (g) which can be rotated. h. Stage.