The cotton bollworms, Helicoverpa armigera (old world bollworm) and Pectinophora gossypiella (pink bollworm), are insect pests of cotton. Adult cotton bollworms are moths. The adult female moths lay eggs on cotton plants. The eggs hatch into larvae. The larvae feed on cotton plants, causing extensive damage and reduction in yield. Fig. 2.1 shows a mature cotton fruit (cotton boll) from an uninfested plant. Fig. 2.2 shows a cotton bollworm inside a developing cotton boll. [Figure 2.1] [Figure 2.2] A gene, cry1Ac, from the bacterium Bacillus thuringiensis (Bt), can be inserted into the cotton genome to produce 1 cry gene Bt cotton. • 1 cry gene Bt cotton produces the protein Cry1Ac, which is toxic to some species of bollworm. This toxicity gives cotton plants some resistance to cotton bollworm. An additional gene, cry2Ab, can be inserted into the cotton genome with cry1Ac. This produces 2 cry gene Bt cotton. • 2 cry gene Bt cotton produces two different proteins, both toxic to cotton bollworm.

1. (a)(i)A trend is a change over time. Describe three trends shown by the data in Table 2.1.[3]
2. (a)(ii)Suggest an explanation for the relationship between growth of Bt cotton and pesticide use on bollworm.[1]
3. (b)(i)Predict and explain the effect of resistance on cotton yield, if the planting of Bt cotton continues to increase.[1]
4. (b)(ii)Experimental observations have shown that planting rows of non-Bt cotton between rows of Bt cotton slows the spread of resistance. Suggest why this pattern of planting can slow the spread of resistance.[2]
5. (c)(i)Identify the independent variable and the dependent variable in this investigation. independent variable dependent variable[2]
6. (c)(ii)Suggest one variable that should be standardised in this investigation.[1]
7. (c)(iii)Non-Bt cotton plants and Bt cry1Ac cotton plants were included as controls in this investigation. Explain why it is necessary to include these plants in this investigation.[2]
8. (c)(iv)The researchers concluded that: 1. The presence of the toxin Vip3AcAa may cause a statistically significant increase in the number of deaths of Bt-resistant larvae. 2. The toxin Vip3AcAa may be equally effective in controlling both types of Bt-resistant larvae. Explain how the data in Table 2.2 support these conclusions.[2]
9. (d)Research has shown that the toxin Vip3AcAa is also effective against Bt-resistant types of P. gossypiella (pink bollworm). Suggest a further investigation that could be carried out to find out if Bt cry1Ac + vip3AcAa cotton is more effective than Bt cry1Ac cotton in controlling pink bollworm.[1]

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