Maths for A Level Biology - updated edition

15 N 14 N Intermediate DNA Light DNA 14 N 15 N 14 N 14 N 14 N 14 N 14 N 14 N 14 N 14 N 14 N 14 N 14 N 14 N Eight molecules, two of which are intermediate and six of which are light. In summary: Generation Number of DNA molecules Number of molecules containing parental strands Number of molecules containing entirely new strands Ratio of molecules containing parental strands : new molecules Parental 1 1 0 1 : 0 1 2 2 0 1 : 0 2 4 2 2 1 : 1 3 8 2 6 1 : 3 4 16 2 14 1 : 7 2.3 The concentration of a solution Knowing the concentration of a solution is important if you study physiology or biochemistry. It is crucial to know what units the concentration is given in. There are two common ways of describing concentration and giving the correct units is vital. 2.3.1 Per cent concentration You may be given a solution of starch labelled ‘1% starch’. The % sign, as always, means ‘out of 100’ so this means there is 1 g of starch in 100 cm 3 solution. You may mix this with a solution of 0.1% amylase, which means the enzyme solution has 0.1 g amylase in 100 cm 3 solution. When you make these solutions, all you have to do is weigh and measure. There are no calculations to be done. But do bear in mind when you make up 2% glucose, it is not 2 g glucose + 100 cm 3 water. When you make a solution, the volume expands and so 2 g glucose + 100 cm 3 water will have a volume greater QUICKFIRE 2.7 a) In the Meselson and Stahl experiment, how many molecules of DNA could be shown to have parental strands after 4 generations of replicating in medium containing 14 N? b) What is the ratio of molecules containing parental strands : new molecules after five generations? Pointer Percentage concentration tells you how many grams in 100cm 3 solution. Mathematics for Biology 42