3.1 Biodiversity and evolutionIB Environmental Systems and Societies SL: Subtopic test

1. 1
   The Cavendish banana supplies almost all of the bananas traded internationally. Cavendish plants are propagated from cuttings, so plantations consist of genetically identical clones. A soil fungus called Fusarium oxysporum f. sp. cubense Tropical Race 4 causes Panama disease, a wilting disease, and has spread through plantations in Asia, Africa and Latin America. There is no effective fungicide. The variety grown before the Cavendish, Gros Michel, was largely lost to an earlier race of the same disease.

   (a)

   Which level of biodiversity describes the variation in alleles between individual Cavendish plants?

   [1 mark]

   • ASpecies diversity
   • BHabitat diversity
   • CGenetic diversity
   • DEcosystem diversity

   (b)

   Which statement best explains why the plantations are so vulnerable to Tropical Race 4?

   [1 mark]

   • AThe plants are genetically identical, so none is likely to carry a resistance allele and the pathogen can infect them all
   • BCloning plants makes the fungus mutate faster
   • CThe plantations contain too many different species for the plants to compete
   • DPlants reproduced by cuttings cannot be attacked by soil fungi until they flower

   (c)

   Suggest how maintaining genetic diversity within banana crops would increase their resilience to disease.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   On Daphne Major in the Galápagos Islands, researchers studied the medium ground finch (Geospiza fortis) for decades. Beak depth varies between individuals and is inherited from parents. In 1977 a severe drought greatly reduced the supply of small, soft seeds, leaving mainly large, hard seeds that only birds with deep beaks could crack. Most of the finches died. In the following generation the average beak depth of the population was greater than before the drought.

   (a)

   Which is a selective pressure acting on the finch population in 1977?

   [1 mark]

   • AMutation of the genes controlling beak depth
   • BShortage of small, soft seeds, causing competition for food
   • CReproductive isolation between island populations
   • DSelective breeding by humans

   (b)

   Which sequence correctly describes natural selection in this population?

   [1 mark]

   • ABirds strained to crack large seeds, so their beaks grew deeper during their lives and this was inherited by their offspring
   • BAll beak depths were equally likely to survive, so the average changed by chance alone
   • CThe drought caused mutations for deeper beaks in every bird that survived
   • DVariation in beak depth, competition for limited seeds, higher survival and reproduction of deep-beaked birds, and inheritance of their alleles

   (c)

   Explain why the average beak depth was greater in the generation after the drought.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Ground beetles were sampled with pitfall traps over the same period in two woodland plots of equal area in England. Plot A is native mixed woodland and Plot B is a plantation of a single conifer species. Five beetle species were recorded in each plot, 50 individuals in total in each. Plot A: species 1 to 5 numbered 12, 11, 10, 9 and 8 individuals. Plot B: species 1 to 5 numbered 38, 6, 3, 2 and 1 individuals. The Simpson's reciprocal index for Plot B was calculated as 1.7.

   (a)

   Calculate Simpson's reciprocal index for Plot A. Show your working.

   [3 marks]

   (b)

   Using the data, compare the species diversity of the two plots and explain why richness alone would not show the difference.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Lake Victoria in East Africa contains hundreds of species of cichlid fish, most of them found nowhere else. Genetic evidence suggests that many of these species evolved over a relatively short geological time from a small number of ancestral populations. The species differ in diet, preferred depth of water and male breeding colours. In the 1950s the Nile perch, a large predatory fish, was introduced to the lake. Populations of many cichlids collapsed and a large number of species are thought to have become extinct. Pollution and nutrient enrichment have also reduced water clarity. Managers deciding what to protect must rely on surveys of which species are present and how many there are.

   (a)

   Explain how evolution by natural selection could have produced the large number of cichlid species in Lake Victoria.

   [6 marks]

   (b)

   Evaluate the extent to which knowledge of the lake's biodiversity is needed to develop effective strategies to conserve it.

   [6 marks]

   Total for question 4: 12 marks

End of questions