Fig. 1 shows a pesticide spray nozzle used above greenhouse tomato plants. Whitefly populations contain variation. A few whiteflies carry an allele that mak...

Fig. 1 shows a pesticide spray nozzle used above greenhouse tomato plants. Whitefly populations contain variation. A few whiteflies carry an allele that makes the pesticide less harmful. A grower sprays one greenhouse weekly but leaves a second greenhouse unsprayed as a comparison. Both greenhouses have similar light, water and temperature conditions. The grower counts whiteflies on 20 leaves each week.

Table 1 shows the mean number of whiteflies per leaf.

(a) Describe the result in the sprayed greenhouse between weeks 6 and 16. [1]
(b) Give a reason for including the unsprayed greenhouse. [1]
(c) Explain the increase in whiteflies in the sprayed greenhouse. [3]

Fig. 1 shows two forms of a weed growing between rows of cereal plants. The farmer uses a herbicide that blocks an enzyme needed for growth. A mutation in some weed cells produces a slightly different enzyme, so these plants are resistant. Seeds from both forms are carried by wind into the next field. The farmer records the number of flowering weeds before collecting the crop.

Table 1 shows the results from one field.

(a) Describe the change in resistant flowering weeds. [1]
(b) Give the source of the original resistance allele. [1]
(c) Complete the chain: resistant weed survives, resistant weed produces seeds, ________. [1]
(d) Explain why herbicide resistance is an example of evolution. [2]