Pre-lab assignment #2. 5 points, winter 2018 DUE WEEK 3 at beginning of lab Yeas

Question

Pre-lab assignment #2. 5 points, winter 2018 DUE WEEK 3 at beginning of lab Yeast Lab (1.5 pt) (0.5 pt) Last week, in order to check the concentration of the yeast suspension, the TAs plated some yeast but did not irradiate them with UV. First, the TA made 10-fold and 100-fold dilutions of tube B yeast (tube B is the same yeast suspension that you used for the UV survival plate). Then, the TA plated 0.1 ml of the 10- fold dilution onto each of 3 plates, and similarly 0.1 ml of the 100-fold dilution onto each of another 3 plates. After incubating the plates for a few days, the TA counted the colonies on each of the plates. Calculate the original concentration of yeast in tube B (in cfu/ml$). Showing work may give you partial credit. Hint: Which set of plates should be used for this calculation? Look ahead to week 3, in the manual. 1· # of colonies on TA's plates SAMPLE 10-fold diluted yeast 227 231 262 23 100-fold diluted yeast Cfu "colony forming unit," which is a living cell or cluster of cells in the original suspension. Each cfu will grow into a colony on a plate.

Explanation / Answer

Mean of 10-fold diluted yeast

262+227+231= 720 /3= 240 x10 (dilution) = 2400 Cfu in 0.1ml x10= 24000

Mean of 100-fold diluted yeast

23+24+22= 69/3 =23 x 100 (dilution)= 2300 Cfu in 0.1ml x10= 23000

(1mL is 10 times 0.1mL   ……..because 0.1x10=1)

The original concentration can be calculated as the mean of the two separate counts, therefore

24000+23000=47000 /2 = 23500 Cfu /ml

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.