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General Biology I Lab Lab #1: Intro, Safety, and Microscopy Instructor: Kristine A. Cooper Introduction This course is a separate, 1 credit laboratory related to the content covered in General Biology I lecture. General Biology I is a pre- or co- requisite. Syllabus Schedule Required & optional materials Attendance Preparation for lab Academic Integrity Grading Course Structure Generally, courses grade on a 50-50 basis, as follows: – 50% of your grade is derived from 5 quizzes, the lowest of which is dropped. – 50% of your grade is derived from two practicals. Course Structure In this course, your grade will be calculated as follows: – 1/3 of your grade will be worksheets given at the beginning of the class and turned in at the end. – 1/3 of your grade will come from five quizzes (none dropped). – 1/3 of your grade will come from two practicals. Grading Specifics Lab reports= 12 @ 25 points = 300 pts Quizzes = 5 @ 60 points = 300 pts Practicals = 2 @ 150 points= 300pts In general, there are NO makeups for practicals or quizzes! Accommodations will be made only in extreme circumstances. Quizzes Quizzes will be given in the test center. They must be taken ON TIME (refer to your syllabus for dates between which quizzes are available) Test center procedures Lab Safety Personal protective equipment – Appropriate attire Extinguishers, fire blankets, eye wash station, emergency shower Chemical & biohazard safety Food, drinks, cell phones Injuries Lab Safety Contract Please fill out both sides of the lab safety contract and place in a pile in the front of the room. Course Introduction Questions so far? Week #1 - Experiment #3 Microscopy Competent use of the microscope is a must for biological study. There is a big difference between using a microscope and using a microscope properly. Types of Microscopes Compound Light Microscope Stereoscopic (dissecting) microscope Scanning Electron Microscope Compound Light Microscope Common, we will use this most in the lab. Compound means two or more lenses are included, one being the ocular and the other the objective. These microscopes can be either monocular (one eyepiece) or binocular (two eyepieces). Parts of the Light Microscope Ocular Body tube Arm Revolving nosepiece Stage clips Objective lenses Stage stop Aperture Stage Coarse adjustment knob Diaphragm Light source Fine adjustment knob Power switch Base Compound Light Microscope These microscopes use transmitted light, which passes through the specimen and to the lens. The total magnification of a compound microscope is calculated by multiplying the magnification of the ocular lens by the magnification of the objective. Magnification Calculating magnification – The ocular lenses in our microscopes are 10x – The objective lenses are 4x (scanning), 10x (intermediate), and 40x (high power). – Therefore, a microscope with a 10x ocular and a 40x objective will have a total magnification of (10 x 40)= 400x Stereoscopic (dissecting) Microscope Used for viewing larger items, such as petri plates or small insects, etc. Most parts are similar to the previously described microscope, although the light sources differ. Magnification is between 10x and 40x. Stereoscopic (dissecting) Microscope These microscopes use reflected or incident light, which is directed at the sample, or transmitted light as in the compound light microscope. Scanning Electron Microscope Most powerful microscope we will cover. Capable of magnifying minute cellular structures. 15x to 200,000x magnification Electrons are the energy source, lenses are electromagnets. Proper care and use Microscopes are stored covered, with their power cords wrapped around them. Carry microscopes CAREFULLY, with one hand under the base and another on the arm. Proper care and use Microscope lenses can be cleaned with lens paper ONLY. DO NOT USE PAPER TOWELS OR KIMWIPES AS THESE WILL SCRATCH THE LENSES. Proper care and use Initially, assure that no objective lenses are in place. The microscopes should be stored this way. Next, wipe your prepared slide clean with a Kimwipe (do not do this for wet-mount slides) and place it on the stage, under the stage clips. Power on your microscope and rotate the 4x objective into place. Proper care and use Look through the ocular and bring your image into focus using the coarse adjustment knob. Raise the condenser to the highest position, then close the diaphragm fully. Looking through the ocular, slowly lower the condenser until the image comes into focus. Proper care and use Slowly open the diaphragm just until the entire field of view is illuminated. These steps are necessary to set your microscope for optimum resolving power. You can now attempt focusing with the 10x. Proper care and use Most microscopes are parfocal, meaning focus should be mostly maintained between objectives. This means little adjustment should be necessary when switching between objective lenses. It is important to NEVER use the coarse focus (fine only) with the high power 40x objective in place. You may break slides or damage the lens. Proper care and use Microscopes must be cleaned and put away properly after use. These are very expensive pieces of lab equipment and their abuse will not be tolerated. Some important points The distance between the specimen being studied and the objective lens is called the working distance. This is very small with the 40x objective in place, which is why we only use the fine adjustment knob. Some important points With higher magnification microscopes, such as those with total magnifications of above 400x, the oil immersion technique is used. A drop of oil with the same refractive index of glass is placed on the top of the slide between it and the objective lens. This reduces two refractive surfaces to one, reducing distortion of the image. Some important points Field of view is the size of the area of the sample that can be seen under a certain magnification. An important relationship: as magnification increases, the field of view decreases. Some important points Depth of field is the thickness of the specimen that can be seen in focus at one time. You may be able to see different aspects (levels) of the same sample at different levels of focus. The higher the magnification, the shorter the depth of field. Resolving power The ability to see two objects of comparable size next to each other and still differentiate them as two separate items. Lower Higher Preparation of a wet mount slide To make a wet mount, a glass slide and cover slip are needed. A small amount of a water-based sample (or sample added to water) is placed on the center of the slide. The cover slip is then gently lowered over the surface of the sample. Preparation of a wet mount slide Don’t use too much sample. Don’t get fingerprints all over the slide and cover slip. Today in Lab Complete exercises 3.1 through 3.4 in your lab manual. Complete your lab report worksheet and hand in before you leave today. QUESTIONS?
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