Lab 7 - Cells - Student Instructions

Biology 1112/2112/2912 - Lab 7 - Cells Student Instructions Learning goals of this week’s lab: ● Develop skills in measuring objects (and cells) under the microscope ● Quantify size differences between prokaryotic (bacteria) and different types of eukaryotic (human) cells Materials required for this week’s lab: 1. Compound microscope 2. Stage micrometer 3. Slide box containing: bacterial types slide, blood smear, adipose tissue cells, thread slide, human cheek smear Overview of Lab & Background: Cells are the basic unit of biological organization. All organisms are composed of at least one cell, and large (multicellular) organisms are composed of many different kinds of cells with various functions. In this lab, we aim to introduce you to quantitative methods for measuring the size of cells, and to develop hypotheses as to what may limit the size of cells. Useful prior knowledge : if you have recently taken BIOL 1111, you may feel comfortable using the microscope. If you have not recently taken BIOL 1111 (or took it online), your lab instructor will review the microscope briefly before you begin your lab. At a minimum, you should be familiar with the following terms: ● Oculars and head ● Arm ● Revolving nosepiece and Objectives (4X, 10X, 40X, 100X) ● Stage and stage adjustment knobs ● Coarse adjustment knob ● Fine adjustment knob ● Condenser ● Iris diaphragm ● Light source Check out this page for a detailed diagram of the microscope. 1

IMPORTANT RULES FOR THE COMPOUND MICROSCOPE 1. Please treat the microscopes with the greatest care! 2. Use only lens paper on microscope lenses. DO NOT USE Kimwipes, tissues, or other papers. 3. Although the eyepiece may be removable, it should not be removed from the microscope. 4. Slides should be placed on and removed from the stage ONLY when the 4X objective is in place . Removing a slide when the higher objectives are in position may scratch the lenses. 5. Do not turn the fine adjustment knob more than two revolutions in either direction. If the image does not come into focus, return to 4X and refocus using coarse adjustment. 6. The microscopes have parfocal lenses, which means that little refocusing is required when moving from one lens to another. Make sure the image is in focus before you change to a higher power objective lens. 7. Never focus with the coarse adjustment knob when you are using the high-power objective. Lab Activities: 1) Activity 1: Calibration of the Ocular Micrometer (OM) The goal of this first activity is to calibrate the ocular micrometer (OM) within your microscope ocular so that you can measure cells that you observe today. When you look through the oculars of your microscope, you will notice that one of the oculars has a grid in it. Although this grid may have numbers, it lacks units and therefore cannot measure in absolute length. Before you can begin measuring cells, you will need to calibrate the grid in the ocular, called the ocular micrometer (sometimes called a graticule ) . This can be accomplished by using a stage micrometer (SM), which measures in absolute units (e.g. millimeters or micrometers) because it has a specific defined length. 2

2) Activity 2: Cell Measurements Use the microscope and ocular micrometer to complete the following tasks. To obtain volume, your instructor can help you determine the correct formula to use. Protocol - Bacterial cells (rectangular boxes) 1. On the bacterial cell type slide, locate the bacilli ( not the cocci or spirilla) and find 5 representative short chains of rods (cells). For each chain, a. measure its length in ocular lines (O.L.) and convert to µm b. estimate the width of a bacillus (you can use the same value for all) c. and count the number of cells. d. Finally, use these data to calculate the average length of an individual bacillus. Enter your data into the table below. 2. Assume that the depth of a bacterium is approximately equal to its width. Rotate the OM to measure, if you need to. Calculate the volume of a bacterium in cc (cubic centimeters) and enter into the table below. Table 1: Bacterial cell measurements Chain # Length (O.L) Length (µm) Width (µm) # of rods 1 2 3 4 5 Average length of an individual bacterium (show your math!): Volume of a bacterium in µm 3 Volume of a bacterium in cc (show your math!): 4

Protocol - Blood cells (cylinders) 1. On the blood smear slide, find 5 representative red blood cells (RBC) and 5 representative white blood cells (WBC). For each RBC and WBC, a. measure its diameter in ocular lines (O.L.) and µm b. And use these data to calculate the average diameter of an individual RBC and the average diameter of an individual WBC. Enter your data into the table below. 2. Assume that a red blood cell is a section of a cylinder with a height = 2 µm. What is the volume of a RBC? Assume that each RBC is packed solidly with Hemoglobin (Hb) molecules. If the volume of a Hb molecule is approximately 3 x 10 -9 µm 3 , how many Hb molecules are there in an average red blood cell? 3. Assume that a white blood cell is a sphere. What is the volume of the average WBC? Table 2: Blood cell measurements RED BLOOD CELLS (RBC) WHITE BLOOD CELLS (WBC) Cell # Diameter (O.L.) Diameter (µm) Cell # Diameter (O.L.) Diameter (µm) RBC 1 WBC 1 RBC 2 WBC 2 RBC 3 WBC 3 RBC 4 WBC 4 RBC 5 WBC 5 RBC average diameter: WBC average diameter: RBC average volume (µm 3 ) WBC average volume (µm 3 ) 5

Fat cell average diameter: Fat cell average volume (µm 3 ) 3) Activity 3: Human Epithelial Cells ( EXTRA CREDIT! Up to 5 points ) Eukaryotic cells are much larger than prokaryotic cells as you demonstrated with the adipose cell measurement above. However, most epithelial cells are not even close to spherical. For this extra credit activity, develop a procedure to measure the volume of what is a thin irregular plate-like (squamous) cell. The area of the flat sides of the cell can be estimated using the print-out on the bench (that contains a scale bar). You can assume that the thickness is 10% of the length. Develop a protocol to measure the volume of this cell and write your protocol in the space provided in Worksheet 7. To Submit from this Lab: 1. Lab 7 In-Class Worksheet 7: Cells - due by midnight on the day of your lab 7