Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

Making serial dilutions

Class practical 

These notes are intended for students making dilutions as part of an investigation, rather than for teachers or technicians who will already know how to do this.

Lesson organisation

Set out and label the glassware before using the solutions.

Apparatus and chemicals

For the students

Solvent for dilution – usually distilled water, but could be ethanol or a standard solution

Graduated pipette, see Note 1

Pipette filler

Health & Safety and Technical notes

This will depend on the nature of the substance you are diluting and the solvent you are using.

1 Graduated pipettes are numbered as a burette – with liquid reaching the zero mark when the pipette is full. This allows you to record exactly how much liquid you have dispensed from the pipette.


SAFETY: Check any relevant hazcards or safety literature for your solvent and the substance under test.

a Label five appropriate tubes (test tubes or boiling tubes – according to how much solution you are making): 1, x10, x100, x1000, x10000

b Measure 11 cm3 of your starting solution into the first tube (labelled 1).

c Use a 10 cm3 syringe or pipette to put 9 cm3 of solvent (such as distilled water) into each of the other tubes.

d Mix the contents of the first test tube thoroughly.

e Remove 1 cm3 of solution from the first tube, into the tube labelled x10.

f Mix thoroughly.

g Remove 1 cm3 of well-mixed solution from the x10 tube into the x100 tube.

h Mix thoroughly.

i Repeat for x1000 and x10000 dilutions.