Maths for A Level Biology - updated edition

The table below shows four different formulae, the results of the calculations and their interpretation. Formula Calculation Interpretation D = 1 − Σ ( n N ) 2 D = 1 − 0.30 = 0.70 Higher number = higher diversity. Maximum = 1 = inϐinite diversity. 0 = no diversity. D = 1 − Σ n ( n − 1) N ( N − 1)  D = 1 − 404 1482 = 1 − 0.27 = 0.73 D =  N ( N − 1) Σ n ( n − 1)  D = 1482 404 = 3.67 Higher number = higher diversity with no upper limit; 0 = no diversity. D =  Σ n ( n − 1) N ( N − 1)  D = 404 1482 = 0.27 Higher number = lower diversity; Maximum = 1 = no diversity; 0 = inϐinite diversity; Calculations such as these are useful for comparing biodiversity in different habitats. For calculating the biodiversity of plants, Disney’s index is commonly used, but neither this nor any of the many other biodiversity indices are required in post- 16 Biology courses, so they will not be discussed here. 2.4.3 Heterozygosity index The heterozygosity index (H) describes biodiversity within a species at the genetic level. The biodiversity of a population is calculated using the equation H =  number of heterozygotes number of individuals in the population . Homozygous plants have either red (RR) or white (WW) ϐlowers and heterozygotes are pink (RW). Imagine a population of snapdragons, of which 300 have red ϐlowers, 300 have white and 600 have pink. For this population, H = 600 300+300+600 = 0.5. 2.5 The haemocytometer The haemocytometer is a modiϐied microscope slide used to count the number of cells in a known volume of liquid. The haemocytometer slide is etched in two places as shown on the left. The cover slip is 0.1mm above the slide and the ruled grid covers a known area. This means that when the cell suspension is introduced into the haemocytometer chamber, you have a known volume of liquid above the grid. When the cells have settled, you count them. Often, the central area marked X on the diagram below is used for counting. Because there are two such ruled areas on the haemocytometer, the exercise can be repeated, to conϐirm the reliability of the counting. Haemocytometer slide Mathematics for Biology 46