Biology Lab #1: Using Microscopes to Observe and Measure Cells

Transcription

1 Biology Lab #1: Using Microscopes to Observe and Measure Cells Make sure you have signed and submitted the CDNIS Safety Contract before you start this experiment! PURPOSE: to review the use of the microscope to learn techniques of estimating the sizes of cells to accurately record observations by preparing biological diagrams to observe and record the structural features of MATERIALS: light microscope lens paper millimeter rulers transparencies of millimeter rulers prepared slides: alveoli red blood cell (sickle cell anemia) striated muscles onion root tip cells adipose cells cardiac muscle cells PROCEDURE A: USING THE MICROSCOPE Identify these parts of a microscope before you start: base arm eyepiece (ocular lens) stage diaphragm condensor coarse adjustment knob fine adjustment knob stage clips body tube revolving nosepiece objective lenses: low power / medium power / high power p. 1

2 Review the correct use of a microscope. You will be assessed on how you use a microscope. a) Carrying a microscope: Use BOTH hands! Hold the with one hand and the with the other hand. b) Setting up a microscope to view a slide: ALWAYS start with the power objective lens. You can find this lens by looking for. Move the stage as far as it can go (without forcing it) by turning the adjustment knob (the dial on the side). Position the slide so that the specimen is over the. Make sure enough light reaches the specimen by adjusting the c) Focusing on a slide: ALWAYS start with the power objective lens. Look at the microscope FROM THE, and turn the adjustment knob so that the stage moves. Now, and only now, look through the, and move the adjustment knob so that the stage moves until the specimen comes into focus. Sharpen the focus by turning the adjustment knob (the dial). When you want to move from low to medium power, do NOT Simply move the Sharpen the image ONLY using the CAREFULLY to the next power. adjustment knob. IF YOU CAN T FOCUS UNDER MEDIUM/HIGH POWER, YOU MUST START AGAIN FROM LOW POWER! d) Make the required observations cell or tissue drawings, measurements of cell sizes, etc. e) When you are finished with your observations: ALWAYS lower the using the adjustment knob. ALWAYS return the objective lens to the setting. ALWAYS the slide and place it Now your turn: use the microscope to view a prepared slide of under MEDIUM power. p. 2

3 PROCEDURE B: PREPARING BIOLOGICAL DRAWINGS Review the requirements for a correct biological drawing. Cell Drawing Rating Scale - in pencil and on unlined paper smooth lines, no shading darker regions shown by stippling clear, neat and on unlined paper drawing is large and easy to see resembles the specimen observed labels lines made with a ruler all visible structures correctly labeled title include specimen name and preparation drawing magnification AND scale bar are correct TOTAL: / 15 This rating scale will be used to assess your biological drawings: TITLE: SCALE BAR (See the next part) DRAWING MAGNIFICATION: (See the next part) p. 3

4 SAMPLE CALCULATIONS PARAGRAPH ON STRUCTURE-FUNCTION RELATION p. 4

5 PROCEDURE C1: ESTIMATING SIZES USING THE MICROSCOPE FIELD OF VIEW DIAMETER 1. Remove the slide used in Part B. Reset the microscope to low power. 2. Identify the magnification for each lens on the microscope: ocular lens (eyepiece) = low power objective lens = medium power objective lens = high power objective lens = 3. Determine the diameter of the field of view of the microscope under LOW POWER. The field of view is the region you see when you look through the microscope. Measure the diameter of the LOW POWER field of view using the millimeter ruler / transparency: Low power field of view diameter = mm = µm 4. Calculate diameter of the field of view (FOV) under MEDIUM & HIGH POWER using these formulas: medium power FOV = low power FOV x (low power mag / medium power mag) high power FOV = low power FOV x (low power mag / high power mag) 5. SUMMARY TABLE FOR DIAMETER OF FIELD OF VIEW MEASUREMENTS objective lens magnification diameter of field of view INCLUDE UNITS! p. 5

6 PROCEDURE C2: ESTIMATING SIZES USING THE MICROSCOPE CELL / OBJECT SIZE 1. Place a slide under the microscope and focus It under LOW POWER. 2. Move the slide so that one edge of a cell is at the LEFT SIDE of the FOV. 3. Estimate the number of cells that would fit side by side across the field of view: fit number = REMEMBER: 1 cm = 10 mm 1 mm = 1000 µm 4. Estimate the actual cell length (or width) using the formula: cell length = diameter of FOV / fit number = = Therefore, the length of the cell is p. 6

7 PROCEDURE C3: CALCULATING DRAWING MAGNIFCATIONS Now calculate the DRAWING MAGNIFICATION: Measure the length of the cell in your drawing on page 3 = Find the estimated cell length as described in Procedure C2 = Make sure the units for both values are the same. If they are not, then convert them: 1 cm = 10 mm 1 mm = 1000 µm Calculate the drawing magnification (by substituting values with the same units only): Drawing magnification = (drawing length) / (estimated cell size) = = Report your drawing magnification at the bottom of your drawing as X Exercise: The estimated size of this cell is mm. Calculate the magnification of this drawing. p. 7

8 PROCEDURE C4: ADDING SCALE BARS TO DRAWINGS Many biological drawings include a scale bar to show the size of the drawing. Example: You should add scale bars to your drawings AS WELL AS indicating the magnification. Choose an appropriate length for a scale bar for your diagram: - Consider the actual length of your cell. - Divide this length into an appropriate scale measurement, like 10 µm, 50 µm, 100 µm. - Determine the length of a scale bar using ratios, as shown below. - Add the scale bar to your biological diagram. Example: Estimate cell size (length) = 40 µm Drawing size (length) = 3.5 cm Using ratios: 40 µm : 3.5 cm 10 µm : x cm 10 µm 40 x = 3.5 x 10 x = cm ASSESSMENT: OBSERVATIONS OF SPECIALIZED CELLS Use the microscope to make observations of one specialized cell type. Include the following: clear, complete and labelled biological drawings of each cell type, including drawing magnification and scale bars be sure to check the Cell Drawing Rating Scale show calculations used to find the drawing magnification for the sample (back of diagram) Write a short paragraph explaining how the shape or structures of your cell type makes it well suited to its function (include citations!!!). Hand this assignment in as a hard copy or scan your drawing and upload it to Moodle MARKS Diagram 15 Magnification and Scale Bar Calculation 5 Paragraph on Structure-Function Relationship 5 p. 8