Classification and biodiversityEdexcel A-Level Biology B: Topic test

1. 1
   Methanocaldococcus jannaschii is a single-celled organism found near deep-sea hydrothermal vents. It has no nucleus, but its ribosomal RNA base sequences are very different from those of bacteria. Researchers who studied these sequences proposed that it belongs to a separate group, the Archaea, and submitted their findings to a scientific journal.

   (a)

   Which sequence lists taxa in the classification hierarchy from the largest group to the smallest?

   [1 mark]

   • AOrder, class, family, genus
   • BClass, order, family, genus
   • CClass, family, order, genus
   • DPhylum, order, class, family

   (b)

   Which evidence supports the three-domain model of classification?

   [1 mark]

   • AArchaea and bacteria differ in cell shape
   • BArchaea have a nucleus, unlike bacteria
   • CDifferences between the ribosomal RNA base sequences of Archaea, bacteria and eukaryotes
   • DArchaea can only live in extreme environments

   (c)

   Explain why the findings were submitted to a scientific journal before being accepted by other scientists.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Emperor penguins breed on the Antarctic ice in winter. Males incubate a single egg on their feet through the winter while the females are at sea feeding. The penguins have a thick layer of blubber, a streamlined body, and they spend the winter huddled together.

   (a)

   Which feature of emperor penguins is a behavioural adaptation?

   [1 mark]

   • AHuddling together in groups during the winter
   • BA thick layer of blubber
   • CA streamlined body shape
   • DA low metabolic rate while fasting

   (b)

   Emperor penguins and Adélie penguins both live in Antarctica but feed on different prey at different depths and breed at different times of year. Which term describes the role of each species in its habitat, including its adaptations, feeding and behaviour?

   [1 mark]

   • AHabitat
   • BPopulation
   • CCommunity
   • DNiche

   (c)

   Explain how natural selection could have led to the evolution of a thicker layer of blubber in the ancestors of emperor penguins.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students sampled the invertebrates in a freshwater pond using a net. They found four species and recorded the number of individuals of each: 12 water boatmen, 8 mayfly nymphs, 5 caddis fly larvae and 3 freshwater shrimps. A second pond, next to a heavily fertilised field, was sampled in the same way and had an index of diversity of 1.8.

   (a)

   Use the formula D = N(N − 1) ÷ Σn(n − 1) to calculate the index of diversity of the first pond. Give your answer to two significant figures.

   [3 marks]

   (b)

   Compare the diversity of the two ponds and suggest a reason for the difference. Explain one limitation of using this index to assess the biodiversity of a pond.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Lake Victoria in Africa contains hundreds of species of cichlid fish that have evolved from a few ancestors in about 15 000 years. Many of the species live in the same part of the lake and have similar body shapes, but males differ in colour. Females generally choose to mate only with males of their own colour. In laboratory tanks, some of the species can interbreed to produce fertile hybrids.

   (a)

   Explain how sympatric speciation could have produced many species of cichlid fish within one lake.

   [6 marks]

   (b)

   Explain why it is difficult to decide how many species of cichlid there are, and how DNA sequencing and the scientific community help to resolve this.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A zoo is running a captive breeding programme for an endangered mammal. Only 30 individuals of the species remain, and the zoo holds 12 of them. Zoos in other countries hold some of the others.

   (a)

   Which is a limitation of conserving a species by breeding it in zoos?

   [1 mark]

   • AAnimals are protected from poachers
   • BAnimals can be bred to increase their numbers
   • CThe small captive population has a restricted gene pool and may be inbred
   • DVeterinary care can be given to animals

   (b)

   Which is a measure of genetic biodiversity within a species?

   [1 mark]

   • AThe number of different alleles in the gene pool of a population
   • BThe total number of individuals in the population
   • CThe number of different species in a habitat
   • DThe number of different habitats in an area

   (c)

   Suggest two ways in which zoos can maintain the genetic diversity of the captive population.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Researchers in Vietnam find a bat in a limestone cave. It looks very like a known species, but it is slightly smaller and has a different call. They extract DNA from the bat and compare it with DNA from the similar known species.

   (a)

   Why is comparing DNA base sequences a more reliable way of showing relationships than comparing physical features?

   [1 mark]

   • ADNA is found only in the species being studied
   • BPhysical features never change
   • CDNA sequencing is always quicker than observation
   • DBase sequences are objective data and are not affected by organisms looking alike because of similar environments

   (b)

   Two bats are placed in the same genus. Which statement must be correct?

   [1 mark]

   • AThey are in different families
   • BThey are in the same family, order and class
   • CThey can interbreed to produce fertile offspring
   • DThey are in the same species

   (c)

   Describe how gel electrophoresis of DNA fragments could be used to show how closely related two species of bat are.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   Multi-drug-resistant tuberculosis (MDR-TB) is caused by strains of Mycobacterium tuberculosis that are resistant to the two most effective antibiotics. Patients must take a combination of drugs for at least six months, but some stop taking them when they begin to feel better. New antibiotics have been developed to treat MDR-TB, and strains resistant to some of these have already been found.

   (a)

   Explain how stopping the course of antibiotics early can lead to the spread of resistant strains of M. tuberculosis.

   [3 marks]

   (b)

   Explain what is meant by an evolutionary race between pathogens and medicines, and suggest one way of slowing it down.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Przewalski's horse is a wild horse that became extinct in the wild in the 1960s. All living animals descend from about a dozen founders held in zoos. Captive breeding has now produced over 2 000 horses, and some have been released into protected reserves in Mongolia. Przewalski's horses have 66 chromosomes and domestic horses have 64, but they can interbreed and produce fertile offspring.

   (a)

   Explain why scientists disagree about whether Przewalski's horse is a separate species from the domestic horse, and how the disagreement can be resolved.

   [6 marks]

   (b)

   Evaluate the captive breeding and release programme as a way of conserving Przewalski's horse.

   [6 marks]

   Total for question 8: 12 marks

End of questions