Biology • Year 12 • Module 6 • Lesson 16
Recombinant DNA Technology and Transgenic Organisms
Apply the toolchain to four real cases — Bt cotton in Australia, Golden Rice, recombinant insulin, and global GMO crop adoption — and reason from real data.
1. Bt cotton in Australia — pesticide-use data
Australian cotton growers began commercial planting of transgenic Bt cotton in 1996. The Bt gene, originally from the soil bacterium Bacillus thuringiensis, codes for a protein toxic to caterpillars of Helicoverpa moths (the main cotton pest). The table below summarises typical industry-reported figures comparing conventional cotton with Bt cotton in NSW and southern Queensland over the period 1996–2018. 7 marks
| Indicator | Conventional cotton (pre-1996) | Bt cotton (by ~2018) |
|---|---|---|
| Insecticide sprays per crop (typical) | ~10–12 | ~1–2 |
| Active insecticide ingredient applied (kg/ha) | ~7.0 | ~0.6 |
| Helicoverpa damage to bolls (typical) | moderate–high | low |
| Yield (relative) | 1.00 (baseline) | ~1.05–1.15 |
| Reproductive method used to produce the crop | conventional breeding + seed | transgenic insertion of Bt gene + seed |
Indicative industry figures (CSIRO / Cotton Australia reporting, 1996–2018).
1.1 Describe the change in insecticide use between conventional and Bt cotton, quoting at least one figure from the table. 2 marks
1.2 Explain how recombinant DNA technology produces a Bt cotton plant. Name the source DNA, the cutting and joining enzymes, the vector role, and the host. 3 marks
1.3 Explain why this transgenic approach was preferred over continued selective breeding to reduce Helicoverpa damage. 2 marks
2. Golden Rice — applied scenario
Golden Rice is a transgenic rice line engineered to produce β-carotene (a precursor of vitamin A) in its grain. Two genes are inserted: psy from maize (Zea mays) and crtI from the soil bacterium Pantoea ananatis. The genes are introduced into rice cells using Agrobacterium tumefaciens as a vector. Adoption is intended for regions where vitamin A deficiency causes preventable childhood blindness. 6 marks
2.1 Identify the donor DNA, the vector, and the host cell type in the Golden Rice example. 3 marks
2.2 Golden Rice is classified as a transgenic organism. Justify this classification using the lesson's definition. 2 marks
2.3 A student claims "Golden Rice could have been produced just as quickly by selectively breeding rice plants for higher β-carotene." Briefly evaluate this claim using lesson content. 1 mark
3. Recombinant human insulin — process reasoning
Before 1982, insulin for diabetic patients was extracted from the pancreases of slaughtered pigs or cattle and purified. Since 1982, almost all medical insulin used in Australia is "humulin": human insulin produced by transgenic Escherichia coli bacteria carrying the human insulin gene on a plasmid vector. 6 marks
3.1 Outline how recombinant DNA technology is used to produce human insulin from E. coli. Use the four toolchain steps from Card 2. 4 marks
3.2 Identify two advantages of recombinant insulin over insulin extracted from animal pancreases. 2 marks
4. Interpret graph — global adoption of GM crops 1996–2018
The graph below summarises the global area planted with genetically modified (GM) crops between 1996 (first year of commercial planting) and 2018. Data are reported in millions of hectares (Mha), based on ISAAA industry reporting. 5 marks
Source: ISAAA GM crop reports, 1996–2018 (indicative).
4.1 Describe the trend in global GM crop area between 1996 and 2018, including approximate start and end values. 2 marks
4.2 Identify the approximate year at which growth begins to plateau, and suggest one agricultural reason this is occurring. 2 marks
4.3 Use the graph to support or refute the lesson's claim that recombinant DNA technology has had significant agricultural applications. 1 mark
Q1.1 — Bt cotton insecticide trend (2 marks)
Insecticide use fell sharply with Bt cotton. Sprays per crop dropped from about 10–12 to about 1–2, and active ingredient applied dropped from ~7.0 kg/ha to ~0.6 kg/ha — roughly a 90% reduction [1 for direction of change, 1 for quoting a specific figure].
Q1.2 — Producing a Bt cotton plant (3 marks)
The Bt (Cry) gene from the soil bacterium Bacillus thuringiensis is the donor DNA [1]. Restriction enzymes cut both the Bt gene and a vector (commonly a plasmid carried in Agrobacterium tumefaciens) at compatible sites, and DNA ligase joins the gene into the vector to produce recombinant DNA [1]. The recombinant vector is then used to deliver the Bt gene into cotton cells (the host cells), which are regenerated into whole transgenic cotton plants that express the Bt protein and become toxic to Helicoverpa caterpillars [1].
Q1.3 — Why transgenic preferred over selective breeding (2 marks)
Cotton does not naturally contain a Bt-toxin gene, so selective breeding cannot generate a Bt-producing cotton plant — there is no existing allele to reshuffle [1]. Recombinant DNA technology inserts the bacterial gene directly into the cotton genome, giving the plant a new trait quickly and precisely instead of relying on decades of cross-breeding that could not produce the trait at all [1].
Q2.1 — Donor DNA, vector, and host in Golden Rice (3 marks)
Donor DNA: the psy gene from maize (Zea mays) and the crtI gene from Pantoea ananatis (a soil bacterium) [1]. Vector: the bacterium Agrobacterium tumefaciens, which carries a plasmid that transfers the inserted genes into plant cells [1]. Host cells: rice cells (which are then regenerated into whole transgenic Golden Rice plants) [1].
Q2.2 — Why Golden Rice is transgenic (2 marks)
Golden Rice contains DNA inserted from sources other than rice — specifically a maize gene and a bacterial gene [1]. The lesson defines a transgenic organism as one that contains inserted DNA from another source, which is exactly what Golden Rice satisfies [1].
Q2.3 — Evaluate the selective-breeding claim (1 mark)
The claim is incorrect. Conventional rice grain does not produce β-carotene at all, so there is no β-carotene-producing allele in the rice gene pool that selective breeding could reshuffle. The trait required insertion of new genes from maize and bacteria, which is exactly what recombinant DNA technology enables and selective breeding cannot [1].
Q3.1 — Producing human insulin in E. coli (4 marks)
Step 1 — Cut. The human insulin gene is isolated, and both the gene and an E. coli plasmid (vector) are cut using the same restriction enzyme, producing compatible sticky ends [1]. Step 2 — Join. DNA ligase seals the human insulin gene into the plasmid, forming recombinant DNA [1]. Step 3 — Insert into host. The recombinant plasmid is taken up by E. coli host cells [1]. Step 4 — Use the result. The transgenic E. coli are grown in large fermenters, where they express the human insulin gene and secrete human insulin, which is then purified for medical use [1].
Q3.2 — Two advantages over animal insulin (2 marks)
Accept any two of: (a) the insulin produced is identical to human insulin so it triggers fewer immune reactions than pig or cattle insulin; (b) E. coli can be grown in large fermenters to produce essentially unlimited quantities, decoupling supply from livestock slaughter numbers; (c) production is more consistent and easier to standardise; (d) lower risk of transmitting animal-derived pathogens; (e) ethically does not require killing animals for extraction. [1 mark per valid advantage, max 2].
Q4.1 — Trend in global GM crop area (2 marks)
Global GM crop area increased dramatically from ~1.7 Mha in 1996 to ~191.7 Mha in 2018, an approximately 100-fold rise [1]. Growth was rapid and roughly linear from 1996 through about 2014, then began to plateau between 2014 and 2018 [1].
Q4.2 — Plateau year and reason (2 marks)
The growth begins to plateau around 2014, after which annual increases are small (185 → 192 Mha) [1]. Accept any one reasonable agricultural explanation, e.g.: market saturation in the major adopting countries (USA, Brazil, Argentina, India, Canada); regulatory restrictions in the EU and parts of Asia/Africa limiting further expansion; the suitable arable land for the main GM crops (soybean, maize, cotton, canola) is largely already in use [1].
Q4.3 — Support / refute the agricultural-applications claim (1 mark)
The graph supports the lesson's claim. The roughly 100-fold rise in global GM area between 1996 and 2018, reaching ~192 Mha, shows that recombinant DNA technology has been adopted at agricultural scale and is therefore a major agricultural application — not just a laboratory technique [1].