IGCSE Biology Variation & selection topical questions

Classify each characteristic as continuous or discontinuous variation.

1. (a)Human body mass[1]
2. (b)ABO blood groups[1]
3. (c)Pea seed shape (round or wrinkled)[1]
4. (d)Human height[1]

Answer the questions about causes of variation.

1. (a)State the usual cause of discontinuous variation.[1]
2. (b)State the causes of continuous variation.[2]
3. (c)Name one environmental factor that could affect human body mass.[1]

Define mutation and name two factors that increase its rate.

1. (a)Define mutation.[1]
2. (b)Name two factors that increase the rate of mutation.[2]

A camel has: long eyelashes; broad, padded feet; the ability to tolerate large rises in its body temperature; and the ability to drink 100 litres of water in minutes.

1. (a)State the environment in which these features are adaptive, giving a reason for one feature.[2]
2. (b)State the term for an inherited feature that helps an organism survive and reproduce in its environment.[1]
3. (c)Suggest why these features help the camel survive long periods without drinking.[1]

Describe the process of natural selection.

1. (a)State what must exist within a population before selection can happen.[1]
2. (b)Explain why organisms produce many offspring.[1]
3. (c)Describe what happens to the better-adapted individuals and their alleles.[3]

A farmer breeds wheat plants for resistance to a fungal disease.

1. (a)Describe the steps of selective breeding the farmer should follow.[3]
2. (b)State why the process must be repeated over many generations.[1]
3. (c)State one condition for the trait to respond to selection.[1]

A student measures the hand spans of 30 classmates and records whether each can roll their tongue.

1. (a)State which measurement shows continuous variation and describe the expected pattern of results.[2]
2. (b)State which characteristic shows discontinuous variation and what its graph would look like.[2]
3. (c)State the causes of the two types of variation.[1]

Cultures of bacteria were exposed to different doses of ionising radiation. The table shows how many mutant cells appeared per million cells. (Supplement)

1. (a)Calculate how many times greater the mutation rate is at 200 Gy than with no radiation. Show your working.[1]
2. (b)Describe the trend shown by the data.[1]
3. (c)Explain what ionising radiation does to DNA.[2]
4. (d)Explain why most mutations are harmful or neutral, but a few can help the species.[2]

Explain where genetic variation in a population comes from. (Supplement)

1. (a)Name four sources of genetic variation.[2]
2. (b)Explain why children differ from their parents even when no new mutation has occurred.[2]
3. (c)State whether a body-builder’s enlarged muscles are passed on to his children. Give a reason.[1]

A plant breeder improves a wheat variety by selective breeding. The mean yield at the start is 4.0 tonnes per hectare; after five generations of selecting the highest-yielding parents each time, the mean yield is 5.5 tonnes per hectare.

1. (a)Calculate the percentage increase in mean yield over the five generations. Show your working.[2]
2. (b)Explain why the breeder repeats the selection over many generations.[2]
3. (c)State one drawback of selective breeding.[1]

A class of 200 students records their heights. The results are grouped in the table.

1. (a)State which height group contains the most students.[1]
2. (b)Calculate the percentage of students between 160 cm and 179 cm tall. Show your working.[2]
3. (c)State the type of variation shown by height, and give two reasons from the syllabus for your answer.[2]
4. (d)State one factor that causes variation between these students.[1]

Explain the adaptive features of xerophytes and hydrophytes. (Extended)

1. (a)Explain two adaptive features of a xerophyte.[4]
2. (b)Explain two adaptive features of a hydrophyte.[3]

Explain how strains of antibiotic-resistant bacteria develop, and how this differs from selective breeding. (Extended)

1. (a)Explain the development of antibiotic resistance as natural selection.[4]
2. (b)State one difference between natural selection and artificial selection.[1]
3. (c)Explain one action doctors take to limit resistant strains.[2]

A beetle population lives on pale tree bark. After a volcanic eruption coats the bark with black ash, the population is resampled 50 years later. (Supplement)

1. (a)Name the process that has changed the population.[1]
2. (b)Explain, step by step, how the change happened.[3]
3. (c)Explain why no individual beetle changed colour during its lifetime.[1]
4. (d)State the original source of the dark-shell allele.[1]