BISC110: Series 1 Lab 2 Tetrahymena Behavior
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Objectives: In this lab you will learn:
- Preparation of solutions
- Scientific observation
- Measurement of specimens using the micrometer
- Hypothesis generation
- Experimental design
Series 1 Lab 2 Tetrahymena behavior
Adapted from Bozzone, M.D., and D.A. Martin 2000. An experimenal system to study phagocytosis. Pages 405-415, in Tested studies for laboratory teaching, Volume 21 (S.J. Karcher, Editor). Proceedings of the 21st Workshop/Conference of the Association for Biology Laboratory Education (ABLE).
In this laboratory, you will be making dilutions of a stock solution of ink and use these dilutions to study the effect of ink on Tetrahymena behavior. The instructions in this lab are intentionally vague so that you will have the opportunity to make scientific observations and develop your own ideas. You will also learn some of the ways that scientific data are evaluated and presented.
PART I: INK AND TETRAHYMENA BEHAVIOR
You will be provided with India ink and live Tetrahymena for this lab. After making the appropriate ink solutions, you will add 1% ink to the Tetrahymena and make observations. Based on your careful observations, you will design an experiment to study how the ink affects Tetrahymena behavior.
A. Preparation of Ink Solutions
A stock solution of India ink is located on your bench in a microcentrifuge tube. Using the India ink and sterile water, prepare 1.0mL each of a 10%, 5% and 1% ink solution. The 1% ink solution will be used in part B, and all three ink solutions will be used in part C.
B. Observations of Tetrahymena and the 1% Ink Solution
1. In a microcentrifuge tube, add 50 ul of the 1% ink solution to 50 ul of live Tetrahymena. Mix gently and record the time. Calculate the final concentration of ink and record in your lab notebook.
2. Add 20 ul of the Tetrahymena and 1% ink solution to a glass slide, add a cover slip and view using the microscope. Record your observations.
3. Do you notice any change in the coloration of the Tetrahymena? Be sure to note the time as soon as you notice a change. Continue observing the Tetrahymena at 5, 10, 20 and 30 minutes. Record your observations in your lab notebook.
4. After 30 minutes, add 20 ul of the Tetrahymena and ink solution to 10 ul of fixative. The fixative will fix the cells, allowing you to observe the Tetrahymena in more detail.
5. Count the number of visible structures in 10 individual Tetrahymena and record this information in your lab notebook.
6. Using the micrometer, measure the size of any clearly visible structures inside the Tetrahymena. Measure at least 1 visible structure from at least 5 individual Tetrahymena. Check with your instructor to be sure that you are measuring the correct structures. How do you think these structures formed?
6. Use a digital camera to take pictures of the fixed Tetrahymena. For at least one photographed cell, be sure to note the size of the cell and one clearly visible structure. Please refer to Appendix J for detailed camera instructions.
C. Hypothesis Generation and Experimental Design
Based on your observations of Tetrahymena in the presence of 1% ink, come up with a hypothesis and design an experiment aimed at exploring the effect of ink concentration on Tetrahymena behavior. You can use the 10%, 5% and 1% ink solutions that you prepared previously. Be sure to include appropriate controls. How many cells do you think you should count? How many replicates should you include? Please read PART II: DATA ANALYSIS and talk to your instructor before you finalize your experimental design.
PART II: DATA ANALYSIS
You will now have the opportunity to present your experimental data in the form of a figure. We will first discuss some important concepts in data analysis.
A. Accuracy and Precision
When carrying out an experiment, it is important to do the experiment more than one time to be sure that your measurements are accurate and as precise as possible. Accuracy is the degree of agreement between the measured value of a particular component and the accepted true value. Precision is defined as the degree of agreement between replicate measurements of the same component. Precise measurements do not necessarily indicate accurate measurements. Figure 1 uses targets to illustrate the difference between accuracy and precision. If the bull’s eyes in the targets below represent the true value, then the darts that are the closest to the center of the target are the most accurate. Darts that are not near the center of the target are not accurate even though they may be very closely grouped together indicating good precision. Finally, the darts that are not near the center or grouped together are neither accurate nor precise. Measured values that are both accurate and precise are the goal of all analytical procedures.
