A-level Biology serial dilutions help needed! Watch

Badges: 2
Report Thread starter 4 weeks ago
Recently we did a practical to find out the effect of enzyme concentration on the rate of reaction. The first thing we had to do was dilute trypsin using serial dilution. It seems like an easy concept and I thought I was doing it right, but looking over at others I was confused.

We had 5 different boiling tubes, the first one containing 2cm cubed of 2% trypsin. In the next 4, we had to fill it with 2cm cubed of water. We then had to move across 2cm cubed of trypsin into the first boiling tube with water, but we still needed 2cm cubed of trypsin for the next part of the experiment so the teacher said to put extra into tube containing just trypsin, so I doubled it and had 4cm cubed in the first one. I only moved 2cm cubed into the first boiling tube containing water, swished it around and then moved 2cm cubed of the solution in that boiling tube to the next one and so on. In the last boiling tube, there ended up being 4cm cubed of solution in total, while in the others there was only 2cm cubed of the solution, which makes sense because you're moving the same volume over each time. But looking at other people's around the class they didn't seem to have double in their last boiling tube, which was the most diluted. Is this right that I would have had double the amount in the last tube or did I go wrong somewhere?

I was also concerned because the last boiling tube was supposed to take the longest to become clear once I added the milk because it was supposed to have the lowest concentration of trypsin, however it became clear faster than most of the other boiling tubes with higher concentrations of trypsin. Overall, my boiling tubes became clear very quickly compared to others in the class but I'm not sure why. Do you think I did the serial dilution wrong and this is why?

Thank you
TSR Jessica
  •  Official Rep
Badges: 16
Report 3 weeks ago
Sorry you've not had any responses about this. Are you sure you've posted in the right place? Here's a link to our subject forum which should help get you more responses if you post there.

Quick Reply

Attached files
Write a reply...
new posts
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.


University open days

  • University of Roehampton
    Department of Media, Culture and Language; School of Education; Business School Undergraduate
    Tue, 19 Feb '19
  • Edge Hill University
    Undergraduate and Postgraduate - Campus Tour Undergraduate
    Tue, 19 Feb '19
  • University of Kent
    Sciences, Social Sciences and Humanities Further education
    Tue, 19 Feb '19

Do you give blood?

Yes (69)
I used to but I don't now (23)
No, but I want to start (313)
No, I am unable to (212)
No, I chose not to (231)

Watched Threads

View All