Biology A Level OCR – Classification and Evolution Exam Questions and Mark
Scheme – Revision Essential
Define continuous variation and give an example - ✔✔✔-A characteristic that can take any
value within a range e.g. the height/mass of a plant
Define discontinuous variation and give an example - ✔✔✔-A characteristic that can only result
in certain values (no in-between values) e.g. an animal's sex - male or female
Define the term 'species' - ✔✔✔-A group of organisms that are able to reproduce fertile
offspring
Explain how MRSA has evolved in modern times - ✔✔✔-MRSA has developed resistance to
many antibiotics - when bacteria replicate, their DNA can be altered and the mutatuion 'S.
aureus' provided resistance to methicillin. When the bacteria were exposed to methicillin,
resistant individuals survived, passing on the allele for resistance and the number of antibiotic-
resistant bacteria in the population increased
Give the five steps of natural selection - ✔✔✔-1 - genetic variation
2 - survival of the fittest
3 - advantageous characteristics are passed on
4 - repeats for each generation
5 - over long periods of time, a new species evolves
Give three causes of genetic variation - ✔✔✔-Alleles; mutations; meiosis (independent
assortment + crossing over); sexual reproduction; chance
Give three sources of evidence for evolution - ✔✔✔-Palaeontology (study of bones),
comparative anatomy (similarities and differences in anatomy) and comparative biochemistry
(similarities and differences in chemical makeup)
Scheme – Revision Essential
Define continuous variation and give an example - ✔✔✔-A characteristic that can take any
value within a range e.g. the height/mass of a plant
Define discontinuous variation and give an example - ✔✔✔-A characteristic that can only result
in certain values (no in-between values) e.g. an animal's sex - male or female
Define the term 'species' - ✔✔✔-A group of organisms that are able to reproduce fertile
offspring
Explain how MRSA has evolved in modern times - ✔✔✔-MRSA has developed resistance to
many antibiotics - when bacteria replicate, their DNA can be altered and the mutatuion 'S.
aureus' provided resistance to methicillin. When the bacteria were exposed to methicillin,
resistant individuals survived, passing on the allele for resistance and the number of antibiotic-
resistant bacteria in the population increased
Give the five steps of natural selection - ✔✔✔-1 - genetic variation
2 - survival of the fittest
3 - advantageous characteristics are passed on
4 - repeats for each generation
5 - over long periods of time, a new species evolves
Give three causes of genetic variation - ✔✔✔-Alleles; mutations; meiosis (independent
assortment + crossing over); sexual reproduction; chance
Give three sources of evidence for evolution - ✔✔✔-Palaeontology (study of bones),
comparative anatomy (similarities and differences in anatomy) and comparative biochemistry
(similarities and differences in chemical makeup)
