RP11- serial dilution + calibration curve

Question 1

Describe how a 1 in 10 dilution is made then used to make a 1 in 1000 dilution of the original liquid culture of bacteria. (3)

Answer 1

1. 1 part culture, 9 parts distilled water/ sterile liquid
2. mix
3. repeat using 9 parts of fresh liquid + 1 part of 10^-1 & 10^-2 dilutions to make 10^-3 dilution

Question 2

A student used a dilution series to investigate the number of cells present in a liquid culture of bacteria.
The student looked at cells in the 1 in 10 dilution during his preliminary work. He decided not to use this dilution to determine the number of cells in the undiluted liquid culture.
Suggest an explanation for the student’s decision. (2)

Answer 2

• count unlikely to be accurate
• ∵ too many cells