UNIT #4: Cell Structure & Func4on PART ONE: Microscopes Four Different Types of Microscopes
Dissec:ng Microscope Uses natural or electrical light source to illuminate an object Lens for magnifica4on Organisms can be viewed dead or alive Up to 40x Views the outer surface details of larger objects that can be seen with our naked eyes Compound Light Microscope Uses electrical light source to illuminate an object Lens for magnifica4on Organisms can be viewed dead or alive Up to 1500x Usually used to view objects that are too small to be seen with our naked eyes
Scanning Electron Microscope (SEM) Uses electrons to scan the surface of extremely small objects Computer creates a 3D image and can add colors A vacuum tube removes dust and debris that may interfere with electrons Only can view dead organisms Up to 100,000X TransmiFng Electron Microscope (TEM) Uses a vacuum tube and a computer to create a digital image of the internal structures of an organism Electrons penetrate the object Only view dead organisms Up to 1,000,000x
PRACTICE: Match the microscope to the descrip:on DISSECTING LIGHT COMPOUND SEM TEM 1. 2D computer image, detailed internal structures magnifica4on up to 1,000,000x TEM 2. Light source needed, can view live specimens Dissec:ng and Compound 3. 3D computer images, detailed external structures, magnifica4on up to 100,000x SEM 4. Light source needed, magnifying lenses magnifica4on up to 1500x Light Compound PRACTICE: Label the parts of the microscope Eyepiece (contains the ocular lens) High-Power Objec4ve Lens Arm Diaphragm (controls amount of light) Coarse Adjustment Knob (moves stage up & down) Low-Power Objec4ve Lens Medium-Power Objec4ve Lens Stage Clips Stage (where the slide is placed) Light source Fine Adjustment Knob (used for fine details) Base (supports microscope)
What is my power? To calculate the TOTAL power of magnifica4on: mul4ply the power of the ocular lens by the power of the objec4ve lens What are the powers of magnifica4on for each of the objec4ves we have on our microscopes? Comparing Powers of Magnifica:on We can see be`er details with higher the powers of magnifica4on, but we cannot see as much of the image. The FIELD OF VIEW decreases as magnifica4on increases. Which of these images would be viewed at a higher power of magnifica4on?
Class Worksheet: MEASURING THE SIZE OF AN OBJECT UNDER THE MICROSCOPE Measuring the Field of View with a Metric Ruler Before we can es4mate the size of an object under the microscope, we first need to know how big the Field of View (FoV) is for the magnifica4on that we are using. Which magnifica4on would you use to most accurately measure the FoV with a metric ruler under a microscope? Why?
Determine the size of the FoV shown This FoV is measured to be approximately: 4.5 mm When we view objects under higher power, their size is much, much smaller than a single millimeter. Therefore, we typically measure objects in a smaller metric unit called a micrometer. 1 mm = 1000 micrometer How big is the FoV in micrometers? 4500 micrometers Es4ma4ng the Size of the Object shown STEP #1: Es4mate how many objects fit across the diameter of the circle (FoV). 3 objects fit across STEP #2: Divide the FoV by the number of objects that fit across. 4500 micrometers / 3 objects = 1500 micrometers Total Magnifica:on: 40x Field of View (FoV): 4500 micrometers
MORE PRACTICE: Es4mate size of object STEP #1: Es4mate how many objects fit across the diameter of the circle (FoV). 6 objects fit across STEP #2: Divide the FoV by the number of objects that fit across. 4500 micrometers/6 objects = 750 micrometers Total Magnifica:on: 40x Field of View (FoV): 4500 micrometers Calcula:ng the FoV under High Power High power is too small to measure the FoV with a metric ruler. We need to do a calcula4on using the known FoV measured from a lower power and the ra4o of magnifica4ons. If we switch from 40X to 400x, then we are magnifying the object 10x more! Think about the ra4o of magnifica4ons. 40:400 ra4o = 1:10 ra4o Therefore, we are seeing only 1/10 of the FoV that we saw under the 40x. Therefore. FoV under 400X = (1/10) * 4500 micrometers = 450 micrometers