# confused with calculation

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#1
what does this mean

the information is given in question ..i don't understand the one part in that information is

0.5 cm3 diluted culture was transferred to agar plate
the liquid culture that transferred was diluted by 1 in 10000.

Can anyone explain to me what is meant by 1 in 10000 here?
or how these values are linked
0
3 years ago
#2
Hi,

If 0.5 cm3 of culture medium was diluted by 1 in 10000, this means that each microlitre of original culture was added to 10000 (technically actually 9999) microlitres of the blank agar in the culture plate i.e. each microlitre (ul) would be added to 10000 X 10-3 millilitres of agar.

The practical outcome of this dilution would be that the number of organisms (bacteria?) in the original culture would be reduced by a factor of 10000. So if you were to view let us say (at a very wild guess) 10 bacteria in a cover plate of area 5 microlitres, there would have been in 5 ul of the original culture 10 X 10000 bacteria; so the concentration of bacteria [in the original mixture] would have been 10 X 10000/5 = 20000 per ul.

Hope this helps.

M (ex-medic)
0
#3
(Original post by macpatelgh)
Hi,

If 0.5 cm3 of culture medium was diluted by 1 in 10000, this means that each microlitre of original culture was added to 10000 (technically actually 9999) microlitres of the blank agar in the culture plate i.e. each microlitre (ul) would be added to 10000 X 10-3 millilitres of agar.

The practical outcome of this dilution would be that the number of organisms (bacteria?) in the original culture would be reduced by a factor of 10000. So if you were to view let us say (at a very wild guess) 10 bacteria in a cover plate of area 5 microlitres, there would have been in 5 ul of the original culture 10 X 10000 bacteria; so the concentration of bacteria [in the original mixture] would have been 10 X 10000/5 = 20000 per ul.

Hope this helps.

M (ex-medic)
yeah thanks it helps a lot

so if i was told that there were 300 bacteria in 0.5 diluted solution by a factor of 10000 and i was asked to find what conc of bacteria was in original
I JUST HAVE TO multiply them all?

10000 X 300=3000000 bacteria
0
3 years ago
#4
Hi,

I am sorry you are struggling with a simple solution involving logic - not your fault: schools these days do not encourage students to think and learn to work out things - the poor students are just brought up to work like machines/computers in an automated categorical way - terrible shame!

As you say, there were 300 bacteria in 0.5 cm3 (?) of the 10000-fold diluted solution - think this way: if half a cm3 (which 0.5 cm3 is, agreed?) contains 300 bacteria, then surely a whole cm3 i.e. (double of the 0.5 cm3) will contain twice as many bacteria, correct? Equals 600 bacteria in one cubic centimetre [one cm3].

But you were also told that this 0.5cm3 of solution was 10000 times weaker than the original i.e. that it had been diluted by a factor of 10000.

SO DO YOU AGREE THAT the original solution (BEFORE DILUTION) would have had many more bacteria? Of course, well done!

NEXT Q: How many more? YES, 10000 times as many!.

= 6 X 10E6 [the figure 6 followed by 6 zeros] which is the same as 6 million bacteria/cm3.

My advice to you, young man, would be to try and understand WHY the teacher is asking you to do certain multiplications or divisions - work out the reasons in ALL sciences AND in maths, AND I PROMISE YOU, THINGS WILL FALL INTO PLACE!

Good luck, and if you need further guidance with any other topic, don't hesitate to tag me!

M (specialist biology tutor)
9
3 years ago
#5
I really don't understand this question at all. I am trying to do it now but can't get my head around it. Where does the 300 come from?
0
3 years ago
#6
There is 300 in the disinfectant concentration of zero, meaning that is how much bacteria is in the 0.5cm liquid culture ( as it says in the question) so if you need to find how much is in 1cm (0.5cm x 2) you have to multiply 300 by 2 which = 600.
The diluted solution ( the bacteria mixed with whatever it is being diluted by) says that there is 1cm of the bacteria in 10,000cm of the whole liquid culutre that is diluted or 10^4.
If you multiply 600 by 10^4, you get 6,000,000

(Original post by kitkat1234567)
I really don't understand this question at all. I am trying to do it now but can't get my head around it. Where does the 300 come from?
0
3 years ago
#7
(Original post by Joyce232000)
There is 300 in the disinfectant concentration of zero, meaning that is how much bacteria is in the 0.5cm liquid culture ( as it says in the question) so if you need to find how much is in 1cm (0.5cm x 2) you have to multiply 300 by 2 which = 600.
The diluted solution ( the bacteria mixed with whatever it is being diluted by) says that there is 1cm of the bacteria in 10,000cm of the whole liquid culutre that is diluted or 10^4.
If you multiply 600 by 10^4, you get 6,000,000
Thanks very much!
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