Haemotography

nina_100

Can anyone explain this technique of counting cells (its for mod 7 AQA)? I don't understand it :redface:

Reply 1

Aired

I'm guessing you mean haemocytometry :p:

?

Basically, the haemocytometer is like a microscope slide, except it has a grid on it. You put enough of the bacterial solution you're using onto the haemocytometer to cover the grid completely. Then you put the slide underneath a microscope, so that you can count the cells.

You use the "north-west rule" when counting cells. All the cells that lie fully inside the grid are counted, and so are those that touch either the north or west sides of the grid. If a cell is touching the south or east walls though you don't count it.

You then have to calculate the volume of the haemocytometer's grid (width x length x depth) So you now know how many bacteria are in say 0.005ml, so to work out how many bacteria there are in one ml you would do...

Number in 0.005ml x (1/0.005)

(You'd change 0.005 for whatever the volume of the haemocytometer's grid is)

Reply 2

nina_100

Yes thats what I meant hehe, I knew I'd got the wrong name! Thankyou- much clearer now, I didn't understand the method of counting them, got it know cheers!!! :hugs: