VIEWING CELLS: USING THE COMPOUND LIGHT MICROSCOPE & STAINS

I. Parts of the Microscope Eyepiece: Lens closest to the eye AKA “ocular” Body Tube: Connects the eyepiece to the objectives

I. Microscope Parts (continued) Low Power Objectives: Shortest lenses High Power Objective: Longest lens; closest to the slide DO NOT USE WITH COARSE FOCUS KNOB

I. Microscope Parts (continued) Stage: Where the slide is placed Stage Clips: Clips that hold the slide in place

I. Microscope Parts (continued) Diaphragm: Adjusts the amount of light entering from the light source onto the specimen Light Source: Provides light to illuminate the specimen

I. Microscope Parts (continued) Arm: Where you should always hold & carry the microscope Base: The bottom of the microscope

I. Microscope Parts (continued) Coarse Adjustment Knob: Roughly focuses the specimen. USE ONLY WITH THE LOW POWER OBJECTIVE Fine Adjustment Knob Sharply focuses the specimen on both low and high power

. . II. Labeling the Parts

II. Labeling the Parts Ocular Body tube Nosepiece Arm Stage Low Power Obj. Med. Power Obj. Stage High Power Obj. Stage Clips Course Adj. Knob Diaphragm Fine Adj. Knob Light Base II. Labeling the Parts

TOTAL MAGNIFICATION Powers of the eyepiece (10X) multiplied by objective lenses determine total magnification.

You Try….. If the ocular of a compound light microscope equals 10x and you are using the low power objective (4x) to observe a plant cell, what is your total magnification?

Image Under the Microscope: IV. Image Appearance When viewing a specimen through a microscope, the image is distorted. What does that mean? Images appear upside-down AND backwards Example: The letter “e”: Image Under the Microscope: Original Image:

FIELD OF VIEW The area of the slide you view through the microscope Magnification increase, FOV decreases As you zoom in you see LESS of the specimen on the slide

Wet Mount Wet Mount: liquid suspension observable under a light microscope Place your specimen on a glass slide. Add 1-2 drops of liquid (water) to the slide. Gently lower a coverslip at an angle onto your wet specimen. This reduces air bubbles.

Wet Mount Slide Adding solution without removing coverslip: 1. Place pipette with stain near coverslip 2. Place piece of paper towel on opposite side of coverslip 3. Add stain/solution from pipette

What are stains? How can we test substances for organic compounds? Chemical Stain: A chemical that is used to make a cell visible (ex: iodine, BTB) Chemical Indicators: A substance which detects the presence of a specific element or compound We can test for any organic compound

Bromthymol Blue Can be a stain OR indicator Stains cells blue Indicates presence of Carbon Dioxide by turning from blue to yellow

Lugol’s Iodine Test Can be a stain or indicator Tests for the presence of Starch A positive test results in the iodine changing in color from red/brown to BLACK As a stain, makes cells appear amber

Benedict’s test Tests for the presence of glucose The solution changes from clear blue to opaque ORANGE in a positive test

Measuring Cell Size We can use microscopes to estimate the size of cells we are looking at If we know the diameter of the field of our field of view we can then estimate the size of the cells 1 meter (m) = 1000 millimeters (mm) 1 millimeter (mm) = 1000 micrometers (µm) 1 meter (m) = 1,000,000 micrometers (µm)

MICROMETERS μm = MICROMETER WHAT DOES A MICROMETER EQUAL? 1,000 μm = 1 mm Conversion: ___mm * 1000 = ____μm

Measuring Field of View 1. Place metric ruler on the microscope stage we can determine how many millimeters the diameter of the FOV is

Estimating the size of a cell: Using your estimate of the diameter of the FOV, you can estimate the size of a cell. Use the formula: Size of cell = diameter of field # of cells How many cells fit across the diameter of the field? ________ If the diameter of the field is 1.5 mm, estimate the size of each cell: _______ mm _______ µm

or ______________(µm) in length if the field of view = 1 mm then onion cells are __________ mm or ______________(µm) in length Field of view Onion cell 1mm (1000 µm) 0.5 500 microns

if the field of view = 0.5 mm or 500µm then these cheek cells would be mm or ______________ µm in length 500 5 100 0.5 mm (500 µm) Human cheek cell