IGCSE Biology Biotechnology & GM notes

Bacteria are the workhorses of biotechnology for two Core reasons: a rapid reproduction rate — some divide every 20–30 minutes, so a small culture becomes an enormous one overnight — and their ability to make complex molecules (proteins and other products) using simple, cheap nutrients.

Supplement: two further points complete the answer: there are few ethical concerns over manipulating and growing bacteria — unlike experimenting on animals — and bacteria contain plasmids, small circles of DNA separate from the main chromosome, which are easy to cut, modify and transfer: the natural tool for genetic modification.

Yeast is a fungus that can respire anaerobically: glucose → alcohol (ethanol) + carbon dioxide. For biofuels, yeast ferments sugars from crops (such as maize or sugar cane) in large tanks; the ethanol produced is distilled off and used as a fuel — a renewable alternative to fossil fuels, made by respiration.

In bread-making, the same reaction has a different star product: the carbon dioxide. Yeast is mixed into dough with sugar and water; as it respire anaerobically, CO₂ bubbles expand the dough, making the bread rise; the alcohol evaporates in baking, and the heat kills the yeast. The dough’s oven spring is literally trapped respiration gas.

Pectinase in fruit juice production: pectin is a jelly-like polysaccharide in plant cell walls that makes fruit pulp cloudy and thick. Adding pectinase digests the pectin, breaking down the cell walls — so juice flows out more easily, more juice is extracted, and the juice is clearer. An investigation can compare juice volumes from pulp treated with pectinase against pulp treated with water at the same temperature.

Biological washing powders contain enzymes — proteases and lipases — that digest protein-based stains (blood, egg) and fat-based stains (grease) into soluble products that rinse away. You can investigate their effect: identical stained cloth squares washed at the same temperature with enzyme solution versus boiled enzyme solution (denatured — no effect) versus plain water. The lesson beyond cleaning: enzymes work at lower temperatures than boiling washes, saving energy and protecting delicate fabrics.

Supplement — lactase and lactose-free milk: lactose is the sugar in milk; lactose-intolerant people cannot digest it, causing discomfort. Lactase is the enzyme that breaks lactose into its two simpler sugars — glucose and galactose — which are easily digested. Passing milk immobilised lactase produces lactose-free milk: sweeter tasting, and safe for the intolerant.

Supplement. A fermenter is a large vessel in which microorganisms are grown to produce useful products at industrial scale: bacteria engineered to carry the human insulin gene produce insulin for people with diabetes; the fungus Penicillium produces the antibiotic penicillin; the fungus Fusarium grows to make mycoprotein, a protein-rich meat substitute (sold as Quorn™).

A labelled diagram to picture: a steel tank with a jacket for temperature control, probes for pH and temperature, an air inlet with a sparger, which releases air as fine bubbles, and paddles that stir the culture so it mixes and oxygenates, a stirrer, nutrient inlet and outlet valve for harvesting. The conditions that must be controlled and why: temperature — kept near the microorganism’s optimum, since too cold slows enzymes and too hot denatures them; pH — held at the optimum for the same enzyme reasons; oxygen — supplied for aerobic respiration of the culture; nutrient supply — food added continuously so growth never starves; and waste products — removed or diluted, since they would poison the culture.

Genetic modification is changing the genetic material of an organism by removing, changing or inserting individual genes. The Core examples: inserting human genes into bacteria, which then produce human proteins (such as insulin); inserting genes into crop plants for herbicide resistance (the crop survives spraying while weeds die); genes for insect-pest resistance (the plant makes its own protection); and genes that improve nutritional qualities (e.g. rice with extra vitamin A precursors).

Supplement. Bacterial production of a human protein, step by step: (1) isolate the DNA making up the human gene using restriction enzymes, which cut the DNA leaving sticky ends (single-stranded overhangs); (2) cut bacterial plasmid DNA with the same restriction enzymes, producing complementary sticky ends; (3) insert the human DNA into the plasmid using DNA ligase, which seals the sugar–phosphate backbones — the result is a recombinant plasmid; (4) insert the recombinant plasmids into bacteria (details not required); (5) multiply the bacteria in a fermenter; (6) the bacteria express the human gene, making the human protein, which is harvested and purified.

The clever part is the sticky ends: because both cuts were made with the same restriction enzyme, the overhangs have complementary bases that pair up — human DNA and plasmid DNA slot together before ligase seals them. The same restriction enzyme for both cuts is what makes the join specific.

Supplement. GM crops — soya, maize and rice are the named examples — bring real advantages: higher yields from plants that resist pests or tolerate herbicides, so less crop is lost and less insecticide is needed; improved nutrition (e.g. vitamin-A-enriched rice) fighting deficiency diseases; and crops that grow in conditions (salinity, drought) that would fail otherwise.

The disadvantages: seeds and technology are expensive, favouring large companies and richer farmers; some consumers and markets reject GM produce, lowering prices; insects feeding on GM crops may be harmed alongside the pests (e.g. pollen landing on wild plants); resistance may evolve in pests or weeds over time; and genes could escape into wild plant populations by cross-breeding, spreading the modification unpredictably. A balanced answer quotes at least one advantage and one disadvantage with reasons.