(a) A student investigated variation in flower colour in pea plants.
The student counted the number of pea plants that had purple flowers and the number of pea plants that had white flowers.
Fig. 6.1 shows the results.
Use the information in Fig. 6.1 and your own knowledge to complete the sentences about variation.
Variation is the …… between individuals of the same species.
Flower colour in pea plants is an example of discontinuous variation. The other type of variation is known as …… variation.
Discontinuous variation results in a limited number of phenotypes with no ……
Discontinuous variation is usually caused by …… only.
The difference between the number of pea plants that had purple flowers and the number of pea plants that had white flowers is ……
The ratio of purple to white flowers in Fig. 6.1 is ……
(b) Some features of organisms show discontinuous variation.
The term discontinuous variation is in the box on the left.
The boxes on the right show some features of organisms.
Draw two lines from ‘discontinuous variation’ to two features that show discontinuous variation.
(c) New alleles for flower colour can arise as a result of genetic change.
(i) State the term used to describe genetic change.
(ii) State one factor that can increase the rate at which genetic change occurs.
(d) Scientists have experimented with genetically modifying pea plants to make them resistant to pea weevils.
Pea weevils are an insect pest.
(i) Suggest why pea plants might be genetically modified to make them resistant to pests.
(ii) State two other examples of genetic modification in crop plants.
▶️ Answer/Explanation
(a)
Variation is the difference(s) between individuals of the same species.
Flower colour in pea plants is an example of discontinuous variation. The other type of variation is known as continuous variation.
Discontinuous variation results in a limited number of phenotypes with no intermediates.
Discontinuous variation is usually caused by genes only.
The difference between the number of pea plants that had purple flowers and the number of pea plants that had white flowers is 61.
The ratio of purple to white flowers in Fig. 6.1 is 3:1.
Explanation: Variation refers to the differences between individuals of the same species. Discontinuous variation shows distinct categories (like purple or white flowers) with no in-between forms, while continuous variation shows a range of values (like height). The 3:1 ratio suggests Mendelian inheritance patterns where purple is dominant over white.
(b)
Explanation: Discontinuous variation shows distinct categories with no intermediates. Blood groups (A, B, AB, O) and seed shape (round or wrinkled) are classic examples. Features like height or mass show continuous variation with a range of values.
(c)
(i) mutation
(ii) ionising radiation or (some) chemicals
Explanation: Mutations are changes in DNA that create new alleles. Factors like radiation or certain chemicals can damage DNA and increase mutation rates. These changes can lead to new traits like different flower colors.
(d)
(i) so that they are not eaten / to increase yield / so that insecticides do not have to be used
(ii) Any two from: make crops resistant to herbicides, improve nutritional qualities of crops, drought resistance, larger size, better taste
Explanation: Pest-resistant GM plants reduce crop losses and pesticide use. Other GM applications include herbicide resistance (letting farmers control weeds without harming crops) and nutritional improvements (like Golden Rice with added vitamin A). These modifications help address food security and nutritional challenges.
(a) (i) State the meaning of the term variation.
(ii) Table 6.1 shows some statements about variation.
Place ticks (✓) in the boxes to show which statements describe continuous and
discontinuous variation.
Place one tick in each row.
(iii) Fig. 6.1 shows graphs of two types of variation.
On Fig. 6.1, state an example of a phenotype for each type of variation shown.
(b) Complete the statements about mutation.
Mutation is a ………… change in which new …………. are formed.
The rate of mutation is increased by some chemicals and by ……….. radiation.
▶️ Answer/Explanation
(a)(i) Variation refers to the differences between individuals of the same species. These differences can be due to genetic or environmental factors.
(a)(ii) 
(a)(iii) The top graph (discontinuous variation) represents traits like blood groups (A, B, AB, O) or seed shape in peas, which have distinct categories. The bottom graph (continuous variation) represents traits like body length or mass, which show a range of values.
(b) Mutation is a genetic change in which new alleles are formed. The rate of mutation is increased by some chemicals and by ionising radiation.