SpeciationAQA A-Level Biology: Subtopic test

1. 1
   Two populations of ground squirrels were once part of one interbreeding population. A river then changed course and now separates them. The squirrels cannot cross the river. The two sides of the river have different vegetation and different climates.

   (a)

   Which term describes speciation that occurs when populations are separated by a geographical barrier?

   [1 mark]

   • AAllopatric speciation
   • BSympatric speciation
   • CDirectional speciation
   • DDisruptive speciation

   (b)

   What does isolation of the two squirrel populations mean for their gene pools?

   [1 mark]

   • ANo new mutations occur in either population
   • BThe two gene pools contain identical alleles
   • CNatural selection stops acting on both populations
   • DThere is no gene flow between the two populations

   (c)

   Explain how, over many generations, the two squirrel populations could become two separate species.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In a meadow, an insect species feeds and mates on two plant species that grow in the same area. One plant species flowers in May and the other flowers in August. Insects that feed on the May-flowering plant breed in May and insects that feed on the August-flowering plant breed in August. Over many generations the two groups of insects have become genetically different.

   (a)

   Which term describes the formation of new species in this way?

   [1 mark]

   • AAllopatric speciation
   • BGene flow
   • CSympatric speciation
   • DGenetic drift

   (b)

   Which observation would show that the two groups of insects have become separate species?

   [1 mark]

   • AThey look different
   • BThey cannot interbreed to produce fertile offspring
   • CThey feed on different plants
   • DThey breed at different times of the year

   (c)

   Explain how the different breeding times could lead to the formation of two species.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Horses and donkeys can mate and produce offspring called mules. Mules are almost always sterile. Horses and donkeys are thought to have evolved from a common ancestral population whose descendants became separated and lived in different regions with different climates and vegetation.

   (a)

   Explain why horses and donkeys are classified as separate species even though they can mate and produce offspring.

   [3 marks]

   (b)

   Suggest how the separation of the ancestral population into different regions could have led to the formation of horses and donkeys as separate species.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A single species of snail lives on a mainland. A few snails are carried on floating vegetation to two islands, A and B, where they found new populations. Island A has dry, rocky habitats and many predatory birds. Island B has dense, damp forest and few predators. Snails cannot cross the sea between the islands and the mainland.

   (a)

   Explain how natural selection and isolation may result in the snails on island A forming a new species.

   [6 marks]

   (b)

   Compare allopatric speciation and sympatric speciation.

   [6 marks]

   Total for question 4: 12 marks

End of questions