Cambridge International A Level Biology Revision Guide

Chapter 17: Selection and evolution
6 Rearrange the order of the following statements to give a flow diagram showing the evolution of resistance to
the antibiotic streptomycin by the bacterium Escherichia coli.
1 Most of the population of E. coli is resistant to streptomycin.
2 A mutation in a DNA triplet of a plasmid, changing TTT to TTG, gives an E. coli bacterium
resistance to streptomycin.
3 The resistant bacterium divides and passes copies of the R plasmid (plasmid with gene for resistance to antibiotic)
to its offspring.
4 Sensitive bacteria die in the presence of streptomycin as a selective agent.
5 The frequency of the mutated gene in the population increases.
6 The resistant bacterium has a selective advantage and survives. [3]
7 Hybrids produced by crossing two different inbred (homozygous) varieties are often more vigorous in their growth
than either of their parents. Copy and complete the flow diagram to show how breeders of maize produce plants
that show hybrid vigour.
Inbred line 1
Genotype: homozygous
Phenotype: uniform
Yield: low
Inbred line 2
Genotype: ..................
Phenotype: ..................
Yield: ..................
Hybrid
Genotype: ..................
Phenotype: ..................
Yield: ..................
[6]
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8 Copy and complete the table to compare artificial selection with natural selection.
Natural selection
the selective agent is the total environment of the organism
adaptations to the prevailing conditions are selected
many different traits contributing to fitness are selected
Artificial selection
[3]
9 Pale and dark peppered moths were collected and placed on pale and dark areas of bark on trees in a park in
Liverpool, England (Figure 17.13, page 406). Some of the moths were predated by birds. The results of the investigation
are shown in the table.
Colour of moth
Percentage of moths taken by birds
from pale bark
from dark bark
pale 20 44
dark 40 15
a 40 dark moths were placed on dark bark. Calculate the number of moths taken by birds. Show your working. [2]
b Suggest an explanation for the differences in the numbers of moths taken by birds. [4]
[Total: 6]