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3. You come into lab and examine your viable count plate. You count 132 bacterial colonies. You check your notes and see that you made the following dilutions of your original culture: 1.0 ml into 9 ml, then 0.1 ml into 9.9 ml and then 0.5 ml into 4.5 ml. You spread 0.2 ml of your final dilution onto your plate. a) What was the original concentration of your sample? (4 points) b) How many mls of the final dilution would you have needed to plate to get about 66 colonies? (2 points) c) What simple technique could you use to check one of the colonies from your plate to see if the bacteria are Gram positive or Gram negative? (2 points) 4. You receive yeast culture of an unknown concentration, so you decide to determine the concentration by performing a direct count using a hemocytometer (counting chamber). You count the number of yeast in seven 1/25 mm2 boxes and get the following results: 16, 18, 20, 21, 19, 22 and 20. a) How many cells per ml are in your unknown sample? (4 points) b) If you diluted your unknown sample 1:100, then 1:10, and then plated 0.05 ml onto a YEPD plate to do a viable count, about how many colonies would you expect? (2 points) 

          3. You come into lab and examine your viable count plate. You count 132 bacterial colonies. You check your notes and see that you made the following dilutions of your original culture: 1.0 ml into 9 ml, then 0.1 ml into 9.9 ml and then 0.5 ml into 4.5 ml. You spread 0.2 ml of your final dilution onto your plate. a) What was the original concentration of your sample? (4 points) b) How many mls of the final dilution would you have needed to plate to get about 66 colonies? (2 points) c) What simple technique could you use to check one of the colonies from your plate to see if the bacteria are Gram positive or Gram negative? (2 points)
4. You receive yeast culture of an unknown concentration, so you decide to determine the concentration by performing a direct count using a hemocytometer (counting chamber). You count the number of yeast in seven 1/25 mm2 boxes and get the following results: 16, 18, 20, 21, 19, 22 and 20. a) How many cells per ml are in your unknown sample? (4 points) b) If you diluted your unknown sample 1:100, then 1:10, and then plated 0.05 ml onto a YEPD plate to do a viable count, about how many colonies would you expect? (2 points)
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3. You come into lab and examine your viable count plate. You count 132 bacterial colonies. You check your notes and see that you made the following dilutions of your original culture: 1.0 ml into 9 ml, then 0.1 ml into 9.9 ml and then 0.5 ml into 4.5 ml. You spread 0.2 ml of your final dilution onto your plate. a) What was the original concentration of your sample? (4 points) b) How many mls of the final dilution would you have needed to plate to get about 66 colonies? (2 points) c) What simple technique could you use to check one of the colonies from your plate to see if the bacteria are Gram positive or Gram negative? (2 points) 4. You receive yeast culture of an unknown concentration, so you decide to determine the concentration by performing a direct count using a hemocytometer (counting chamber). You count the number of yeast in seven 1/25 mm2 boxes and get the following results: 16, 18, 20, 21, 19, 22 and 20. a) How many cells per ml are in your unknown sample? (4 points) b) If you diluted your unknown sample 1:100, then 1:10, and then plated 0.05 ml onto a YEPD plate to do a viable count, about how many colonies would you expect? (2 points)

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Biology for AP Courses
Biology for AP Courses
Julianne Zedalis, John Eggebrecht
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3. You come into lab and examine your viable count plate. You count 132 bacterial colonies. You check your notes and see that you made the following dilutions of your original culture: 1.0 ml into 9 ml, then 0.1 ml into 9.9 ml and then 0.5 ml into 4.5 ml. You spread 0.2 ml of your final dilution onto your plate. a) What was the original concentration of your sample? (4 points) b) How many mls of the final dilution would you have needed to plate to get about 66 colonies? (2 points) c) What simple technique could you use to check one of the colonies from your plate to see if the bacteria are Gram positive or Gram negative? (2 points) 4. You receive yeast culture of an unknown concentration, so you decide to determine the concentration by performing a direct count using a hemocytometer (counting chamber). You count the number of yeast in seven 1/25 mm2 boxes and get the following results: 16, 18, 20, 21, 19, 22 and 20. a) How many cells per ml are in your unknown sample? (4 points) b) If you diluted your unknown sample 1:100, then 1:10, and then plated 0.05 ml onto a YEPD plate to do a viable count, about how many colonies would you expect? (2 points)
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Transcript

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00:01 So let's start from question number three.
00:03 So you come into lab and examine your viable count plate.
00:06 You count 132 bacteria colonies.
00:09 And you check your note and see that you made the following dilution of your original culture.
00:14 So first of all, you did 1 .0 milliliter into 9 militer, which means 1 plus 9 equals 10.
00:27 So you go from 1 millimeter to 10 militer in total.
00:34 Concentration drops 10 times when the volume increase 10 times.
00:39 So this is a 1 to 10 dilution.
00:41 Second, then 0 .1 militer into 9 .9 millimeter.
00:45 So 0 .1 militer divide by total of 0 .1 plus 9 .9 milliter.
00:56 This also will give you a 10 militer.
00:59 So 0 .1 militer to 10 militer in total.
01:09 So this is a 1 to 100 dilution.
01:12 The third step, 0 .5 mil into 4 .5 mil.
01:16 So the third dilution, you go from 0 .5 militer to 0 .5 plus 4 .5 militer, which is 5 in total.
01:29 So 0 .5 to begin with, and the final volume 5 milliliter, again, the volume increased 10 times, the concentration drops 10 times.
01:42 So it's again a 1 to 10 dilution.
01:44 So you did 1 to 10, then you did a 100, then you did a 1 to 10 dilution again.
01:50 Now you spread 0 .2 militer of your final dilution into your plate.
01:55 What was the original concentration of the sample? so first of all, you want to calculate a diluted sample.
02:03 So diluted sample, you have the colony divided by the volume.
02:10 So we know that we have 132 colony to begin with, and then we spread it 0 .2 mil.
02:22 So all you have to do is do your mass 132 plus .2 equals 660.
02:32 Colony form unit per mill liter.
02:35 Now this is the diluted concentration.
02:39 However, if we want to calculate the concentration of original, you're going to have to take diluted sample times dilution factors.
02:57 So you have 660 cfu per mill times three dilution, 10, 110.
03:06 So this gave you 10 to the 4th, 660 times 10 to the 4th, which will be 6 .6 times 10 to the 6 .6.
03:23 So you move decimal and add 2 on an exponent, cfu per militer.
03:31 So this is the original concentration.
03:35 What sample, how many milliliter of the final dilution would you have to need to plate to get about 66 colony.
03:45 So we can actually look.
03:47 For the final dilution, you take 0 .2 milliter, which will give you 132.
03:56 This is b.
04:00 Colonies.
04:03 And now if you need 66, that means you need only half of the cell.
04:14 So 132 divided by 2, obviously, 66 and also the same thing 0 .2 million divided by 2 as well so all you need is use 0 .1 millimeter of the final dilution and then it will give you 66 colonies in the plate the last question what sample technique would you use to check one of the colony from your plate to see if the bacteria are gram positive or gram negative so what you're going to do is you're going to use a dye called the gram stain.
04:56 The gram stain is a good way to differentiate the gram positive and gram negative bacteria.
05:05 So it's purple in color.
05:10 So if the bacteria stays purple, this is gram positive.
05:25 Now if you stain the bacteria colony with gram stain the bacteria, the bacteria all right, so now we finish the first question.
05:50 Let's move on to four.
05:53 So you receive yeast culture of a non -concentration...
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