Biology 2290F/G Study Guide - Optical Axis, Dichlorophenolindophenol, Chlorella
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FOR #4 A & B I don't know if I did it correctly.....Please check & the other questions I'm having a heard time on. Thanks!
A. You have been given a tube of E. coli. You are asked to make 1 mL total volume of 10-1 dilution of the bacterial culture. Explain how you would do this. Show all necessary calculations.
____ ml cells + _____ ml water = 1 ml (total volume)
V1 D1 X V2 D2
1 mL X 1 = V2 X 10^-1
V2 = 1 mL/10^-1 so V2 = 10 mL.
But because V1 is part of V2. The answer is: 10 mL-1 mL= 9 mL of diluent must be added.
V1 D1 X V2 D2
1 mL X 1 = V2 X 10^-2
V2 = 1 mL/10^-2 so V2 = 100 mL.
But because V1 is part of V2. The answer is: 100 mL-1 mL= 99 mL of diluent must be added.
You have bacteria at a concentration of 5 x 108 CFU/mL. You spread 1 mL of this sample on an agar plate to obtain isolated colonies. How many colonies do you expect to find the next day after incubation at 370C? Can you count these colonies? Can you use this plate for determining concentration?
A. You have bacteria at a concentration of 1 x 103 CFU/mL (in real life â you donât know this, but we are just working on math skills here). You transfer 1 mL of this sample into 9 mL of water and then spread 1 mL on a plate of agar. How many colonies do you expect to find the next day after incubation at 370C? Can you count these colonies? Can you use this plate for determining concentration?
You take 0.05 mL of a culture of bacteria at a concentration of 4 x 107 CFU/mL, and add 4.95 mL of water to it. What is the dilution that you have performed? What is the concentration of bacteria (CFU/mL) in the diluted culture?
A. You have diluted a sample by 1000 fold (1/1000) and plated 1 mL on an agar plate. You observe 55 colonies. What was the concentration of the original sample in CFU/mL?
A. A bacterial sample has a concentration of 3 x107CFU/mL. You make serial dilutions of 10-3 followed by 10-2 and 10-1 dilutions. You finally plate 1 mL of the last dilution on an agar plate and incubate it at 370C. What is the total dilution? How many colonies do you expect to see on the plate?
Total dilution:
# of colonies expected on plate:
C. This time, you see 10 times fewer colonies than you had expected to see.What could have gone wrong? How will you fix this problem?
A bacterial sample has a concentration of 2 x106 CFU/mL. Show a scheme of dilutions to obtain 30-300 colonies on a plate. Your scheme should contain the volume of diluent (sterile water), volume of sample transferred each time, the concentration of bacteria (CFU/mL) in each dilution. You can assume you are plating 1 mL of the dilution on plates of nutrient agar. See Figure 1 in protocol.
These are the results of the experiment described in the protocol. From the data shown in the results section of Standard Plate Count protocol, calculate the concentration of bacteria (CFU/mL) in the original sample of E. coli. Show your calculations. Hint: remember that we donât use plates that have less than 30 or more than 300 colonies to do these calculations.
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 âCONTROLâ.
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 â control | YES | NO | 0 | 0 |
2 â 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 donât 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?