A-LevelBiologyGenetic technology9700/43 · May/June 2021 · Q411 Marks

Bt maize has been genetically engineered to resist insect attack. In 2019, Bt maize formed 83% of the maize grown in the USA. Outline how the genetic engineering process produced Bt maize plants with resistance to insect attack.

(a)Bt maize has been genetically engineered to resist insect attack. In 2019, Bt maize formed 83% of the maize grown in the USA. Outline how the genetic engineering process produced Bt maize plants with resistance to insect attack.[5]
(b)(i)A proposed conservation benefit of Bt maize is that, unlike chemical insecticide sprays, it should not harm non-target insects. When Bt maize was first grown in the USA, scientists were concerned that maize pollen containing the Bt toxin might be deposited by the wind on wild plants such as milkweeds, Asclepias spp. Milkweed leaves are the food source of caterpillars (larvae) of the monarch butterfly, Danaus plexippus. In 1999, a laboratory experiment tested the effects of feeding milkweed leaves treated in different ways to the caterpillars of monarch butterflies. Each group of caterpillars was provided with milkweed leaves to eat throughout the experiment. The three different treatments were: • leaves with no pollen • leaves dusted with pollen from non-Bt maize • leaves dusted with pollen from Bt maize. Fig. 4.1 shows the results of this laboratory experiment. [Figure 4.1] State what can be concluded from Fig. 4.1.[2]
(b)(ii)Laboratory results are not always useful in predicting what will happen in real ecosystems. • Some scientists predicted that increasing the area of Bt maize in the USA would decrease the number of monarch butterflies, based on the results in Fig. 4.1. • More monarch butterflies were counted in 2019 than in 1999, even though the quantity of Bt maize grown more than tripled. Suggest reasons why the predicted decrease in the number of monarch butterflies did not occur in the real ecosystem.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[1] (a) gene / DNA, from Bacillus thuringiensis ;
[1] (a) ref. to restriction, enzyme / endonuclease ;
[1] (a) clone gene/ amplify gene, using PCR ;
[1] (a) insert, gene / DNA, into plasmid ;
[1] (a) add promoter ;
[1] (a) seal (plasmid) using DNA ligase ;
[1] (a) (maize) tissue / cell / callus / embryo, takes up plasmid / recombinant DNA ;
[1] (a) (maize) expresses new gene / produces Bt toxin;
[1] (a) AVP; e.g. Ti (plasmid) / Agrobacterium tumefaciens
[1] (b)(i) pollen from Bt maize, kills / is toxic to / harms, caterpillars ;
[1] (b)(i) pollen from non-Bt maize, does not kill / is not toxic to / does not harm, caterpillars ;
[1] (b)(i) (eating) leaves with no pollen does not kill / is not toxic to / does not harm, caterpillars ;
[1] (b)(i) more days of eating pollen from Bt maize gives more caterpillar deaths / AW ;
[1] (b)(ii) Bt pollen did not get deposited (onto milkweed plants) / AW;
[1] (b)(ii) caterpillars and Bt maize located in different areas;
[1] (b)(ii) pollen released at a different time to when caterpillars feed ;
[1] (b)(ii) ref. to caterpillars develop resistance (to Bt toxin);
[1] (b)(ii) ref. to lab and, quantity / toxicity, of Bt pollen;
[1] (b)(ii) AVP; e.g. in 2019 breeding conditions were better than in 1999 e.g. herbicides may reduce milkweed availability in maize fields