Natural selectionIB MYP Biology: Subtopic test

1. 1
   In the nineteenth century two naturalists, Charles Darwin and Alfred Russel Wallace, worked separately in different parts of the world. Darwin collected animals and plants in South America and on the Galápagos Islands. Wallace collected specimens in the Amazon rainforest and the islands of South-East Asia. Both noticed that members of the same species differ from one another, and that parents produce many more offspring than can possibly survive. In 1858 their ideas were presented together to a scientific society in London.

   (a)

   Which observation is a key part of the theory of natural selection that both naturalists proposed?

   [1 mark]

   • AAll individuals of a species are identical
   • BIndividuals of the same species show variation
   • CParents usually produce only as many offspring as can survive
   • DOrganisms never change over time

   (b)

   Which statement best describes the phrase 'survival of the fittest'?

   [1 mark]

   • AThe strongest individuals always win fights and survive
   • BThe oldest individuals in a population survive longest
   • CAll individuals survive if they try hard enough
   • DIndividuals best suited to their environment are more likely to survive and reproduce

   (c)

   Explain why the production of more offspring than can survive leads to competition.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Before the 1840s, almost all the peppered moths in the English city of Manchester were pale with dark speckles. Dark moths were extremely rare. As factories burned coal, soot blackened the tree trunks where the moths rested during the day, and birds hunted the moths by sight. By 1895 about 98% of the peppered moths in the city were dark. After clean-air laws reduced soot in the 1960s, the trunks became paler again, and the pale form became common once more.

   (a)

   Why did the dark form of the peppered moth become more common in Manchester?

   [1 mark]

   • ADark moths were better camouflaged on the sooty trunks, so fewer were eaten by birds
   • BDark moths were stronger than pale moths
   • CThe soot caused the pale moths to change colour
   • DBirds preferred to eat dark moths

   (b)

   Which statement explains how the dark form first appeared in the moth population?

   [1 mark]

   • AThe moths needed to be dark so their bodies made a dark allele
   • BPale moths that were covered in soot passed the dark colour on to their offspring
   • CA random change in a gene (a mutation) produced a new allele for dark colour
   • DPale moths chose to become dark when the trees darkened

   (c)

   Explain why the pale form became common again after the clean-air laws.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A class models predation using paper dots. They scatter 50 red and 50 green paper dots of identical size on a large area of short green grass. Each student acts as a bird and has 30 seconds to pick up as many dots as possible, one at a time. The dots left behind are 'survivors'. Over the whole class, 36 red dots and 18 green dots were picked up in the first round.

   (a)

   State a testable hypothesis for this investigation, give a scientific reason for it, and identify the independent variable.

   [3 marks]

   (b)

   Calculate the percentage of the red dots and of the green dots that were picked up. State whether the results support your hypothesis, quoting the data, and suggest one change that would make the results more reliable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital in Nairobi treats many patients with bacterial infections. Doctors have noticed that an antibiotic that once cured a skin infection caused by one species of bacterium now often fails. Laboratory tests show that most bacteria from recent patients carry an allele that makes them resistant to the antibiotic. The hospital is also considering a new policy that would stop doctors prescribing antibiotics unless a laboratory test shows the infection is bacterial. Antibiotics are also widely given to farm animals in the region.

   (a)

   Explain how a population of bacteria can become resistant to an antibiotic through natural selection.

   [6 marks]

   (b)

   Discuss and evaluate the hospital's proposed policy of prescribing antibiotics only when a laboratory test shows the infection is bacterial. Give a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions