BIOL 1001 Lecture Notes - Lecture 1: Coleus, Absorbance, Aust
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yeast population dynamics
Procedure
1. Work in pairs on this lab, so 12 tubes per pair of students. And share a tube rack with one other pair of students
2. Turn on your spectrophotometer. It needs at least 15 minutes to warm up to give you good readings.
3. Add 5 mL of yeast extract solution (YECM) to each of 12 tubes. (The yeast extract provides vitamins and amino acids for yeast growth and will be the same for all cultures). The tubes should be labeled with your initials, treatment, and tube number. Tape or Parafilm down the lids of 3 tubes, and label them “CONTROL”.
Do not touch the insides of the tubes or lids! Try to keep these as sterile as possible!!
4. Add 50 mL live yeast culture to each of the remaining 9 tubes.
5. Add the varying volumes of sugar and/or ethanol using Table 1 below.
6. Use Parafilm to close the tops of each tube, making sure the Parafilm is tight and no air can get in, and label each tube with the following:
Amount of sugar added (mL) Amount of ethanol added (mL)
Name of your group Tube number
| Table 1: setup yeast tubes (remember, 1 mL = 1000 mL) | ||||
| Tube number | Yeast culture medium? (5 mL) | Live yeast culture? (50 mL) | Sugar added (mL) | Ethanol added (mL) |
| 1 – control | YES | NO | 0 | 0 |
| 2 – control | YES | NO | 0 | 0 |
| 3 - control | YES | NO | 0 | 0 |
| 4 | YES | YES | 0 | 0 |
| 5 | YES | YES | 0.25 | 0 |
| 6 | YES | YES | 0.5 | 0 |
| 7 | YES | YES | 0 | 0.25 |
| 8 | YES | YES | 0.25 | 0.25 |
| 9 | YES | YES | 0.5 | 0.25 |
| 10 | YES | YES | 0 | 0.5 |
| 11 | YES | YES | 0.25 | 0.5 |
| 12 | YES | YES | 0.5 | 0.5 |
Procedure for measuring absorbance (in absorbance units, or AU)
7. Calibrate the spectrophotometer:
Turn on the spectrophotometer and let it warm up for 15 minutes. You will get erroneous results if you don’t let it warm up first.
Be sure the spectrophotometer is set to read at the wavelength of 550 nm
With no tube in the spectrophotometer and the lid closed, use the left-hand knob to adjust the reading to 0% Transmittance/push zero button to calibrate
Insert a CONTROL tube (making sure it is clear, without bacterial contamination which would make it cloudy), and use the right-hand knob to readjust the spectrophotometer to 100% Transmittance.
When reading the absorbance, be sure to line up the needle on the spec with its reflection.
8. Immediately before reading any tube, vortex the tube so that the spinning column reaches the bottom of the tube for several seconds. This is critical! The yeast cells are heavy and will tend to sink to the bottom of the tube, so you must vortex the tubes to resuspend them: otherwise, your spectrophotometer readings will be erroneously low. If the vortex is not enough to suspend the pellet of yeast cells at the base of the tube, take a piece of Parafilm and cover the top of the tube, then cover this with your thumb and shake the tube vigorously. The pellet should dislodge and the yeast cells should be easily resuspended after doing this. Use a Kimwipe to wipe down the outside of each tube, to remove fingerprints and other smudges that could affect the absorbance reading. (COULD BE A POTENTIAL ERROR)
9. Record the absorbance (in absorbance units, AU) for the tube on your data sheet.
10. Repeat steps 5 and 6 for every tube.
11. Leave the spectrophotometer turned on for the next user.
Figures you should include are:
Average absorbance vs. time for the no ethanol (0 mL) treatment
Average absorbance vs. time for the 0.25 mL ethanol treatment
Average absorbance vs. time for the 0.50 mL ethanol treatment
Sugar added vs. average carrying capacity (K). Use different symbols to denote each of the three alcohol concentrations
A. After a limit, the increasing concentration of sugar decreases the carrying capacity and growth rate. This is because at higher sugar concentrations, the medium becomes hypertonic and the yeast cells loss water towards the medium.With increasing concentration of the ethanol, the carrying capacity and the growth rate decreases. Why does this happen?
B. Is there any interaction between the effects of adding sugar and alcohol on yeast?
C. why do some cultures not reach K?
D. What are the potential sources of error and assumptions made in this experiment?
E. What do these results mean in a more general (non-yeast) context?
Instructions:
Read the scientific inquiry below. Use the data and your scientific knowledge, to complete the questions in each of the sections on the rest of this document. Place your answers, in the space provided and bold or change the color of the text of your answer. Once the assignment is complete, save it as a PDF document file. To submit this assignment, email the completed PDF document to your instructors email address by the due date/time. This assignment is to be done individually. Per the Angelina College student handbook, plagiarism will be will not be tolerated.
Scientific Inquiry:
A farmer wishes to determine which of the two fertilizers, Brand X or Brand Y, helps his corn crops grow at a faster rate in a five-week period of time. He asks his daughter, whom is a college freshman taking introductory biology, to design an experiment to help him test each fertilizer. They decide to grow three different crops of corn, each grown in a controlled environment, receiving the same amount of sunlight, same climate, soil type, and water. Crop 1 will receive no fertilizer during watering. Crop 2 will receive Brand X fertilizer while watering. Crop 3 will receive Brand Y fertilizer while watering. The farmer and his daughter performed the experiment and collect data on each fertilizer over a five-week period. Use the data, represented in Table 1, to complete the following assignment.
Table 1. Average height of corn plants when treated with Brand X or Brand Y fertilizer compared to corn plants not treated with fertilizer (control).
| Time (T) in weeks | Control (cm) | Brand X (cm) | Brand Y (cm) |
| 0 | 0 | 0 | 0 |
| 1 | 1.3 | 1.4 | 1.2 |
| 2 | 2.4 | 2.7 | 2.3 |
| 3 | 4.2 | 8.3 | 7.3 |
| 4 | 6.8 | 12.4 | 8.2 |
| 5 | 8.7 | 16.8 | 11.6 |
Section 1: Representation
Define each term or variable, with respect to the scientific inquiry.
Independent variable-
Dependent variable-
Control group-
Experimental group(s)-
Hypothesis-
Write the equation to determine the average growth rate, with the appropriate values included, for each corn crop type (control, Brand X, and Brand Y). Use the equation shown below.
Growth rate = (T5 – T0)/5
Control =
Brand X =
Brand Y =
Section 2: Calculation
Solve the equations generated, in question 2, for each corn crop type. You must show your work, in the space below, for full credit.
Control =
Brand X =
Brand Y =
Section 3: Interpretation
Analyzing the data table and the calculated growth rates, complete the following questions.
Which crop type grew the fastest? Explain your answer using factual information.
Which plant was tallest? Explain your answer using factual information.
What can you conclude about the treatment of fertilizer on crop growth? Explain your answer using factual information.
Section 4: Application and Analysis
What could happen if the temperature were not controlled during the experiment? Would this impact treatment effectiveness on plant growth? Explain your answer.
Do you think the same outcome would occur if pine trees were used? Explain your answer.
If a particular fertilizer works on corn crops, should we be using that fertilizer on all plants? Why or why not?
