Laboratory Techniques For Biologists: Liquids and Solutions

Question 1

Linear dilution series

Answer 1

Dilutions can be sued to control potential confounding variables in an experimental system, to generate a suitable range in an independent variable or as a way of modifying the dependent variable, so that a measurable value can be obtained

Dilutions in a linear dilution series differ by an equal interval, for example 0·1, 0·2, 0·3 and so on.

Dilutions in a log dilution series differ by a constant proportion, for example 10-1, 10-2, 10-3 and so on.

Question 2

Colorimeter

Answer 2

Calibration with appropriate blank as a baseline; use of absorbance to determine concentration of a coloured solution using suitable wavelength filters; use of percentage transmission to determine turbidity, such as cells in suspension.

quantify concentration and turbidity

Question 3

Standard Curve for determining the unknown

Answer 3

Plotting measured values for known concentrations to produce a line or curve allows the concentration of an unknown to be determined from the standard curve.

Question 4

Buffers to control pH

Answer 4

Addition of acid or alkali has very small effects on the pH of a buffer, allowing the pH of a reaction mixture to be kept constant.