Why bacteria are used in biotechnology: the standing list

This exact list is examined repeatedly. Bacteria are used because they:

  • reproduce rapidly, so large numbers are produced quickly;
  • have plasmids, which can be used as vectors to insert genes (useful for genetic modification);
  • can make complex molecules and will use a wide range of nutrients (including waste materials);
  • have few ethical concerns compared with using animals;
  • lack the cell structures (membrane-bound organelles) that would complicate extracting the product.

A bare 'bacteria are small and grow fast' scores one mark; the plasmid and rapid-reproduction points are where the marks concentrate, especially in genetic-modification contexts.

Anaerobic respiration in industry: yeast and bacteria

Two named applications connect straight back to respiration. Yeast respires anaerobically (glucose → alcohol + carbon dioxide): the alcohol is used in brewing and the carbon dioxide makes bread rise (the dough's bubbles). Bacteria in biogas/yoghurt production are the other context. For the bread/brewing question, name the process (anaerobic respiration / fermentation in yeast), give the products, and link each product to its use (CO2 → dough rises; ethanol → alcoholic drinks). A common application question uses a fermenter diagram and asks why conditions (temperature, pH) are controlled. To keep enzymes at their optimum and the microorganisms respiring efficiently.

Genetic modification: what it is and why it matters

Genetic modification (genetic engineering) is changing the genetic material of an organism by removing, changing or inserting individual genes. The headline benefit is that a gene from one species can be put into a completely different species, which then makes the desired protein. Examiners want the principle stated cleanly: the inserted gene still codes for the same protein because the genetic code is universal. A bacterium given the human insulin gene will make human insulin. Examples to know: insulin production, herbicide-resistant or pest-resistant crops, and crops with improved nutrient content.

Making human insulin: the sequence in order

The flagship process. State the steps in order:

  1. The human insulin gene is identified and cut out of human DNA using enzymes (restriction enzymes).
  2. A bacterial plasmid is cut open with the same enzyme, leaving complementary 'sticky ends'.
  3. The insulin gene is inserted into the plasmid and joined using an enzyme (ligase); the plasmid is now a recombinant vector.
  4. The plasmid is put back into a bacterium.
  5. The bacteria are grown in a fermenter, reproduce rapidly, and each expresses the gene to make insulin, which is extracted and purified.

The detail examiners reward: the same enzyme cuts both the gene and the plasmid so the ends are complementary, and the bacteria's rapid reproduction is what makes large-scale production possible. You are not required to name every enzyme at Core level, but knowing 'cut with enzymes, joined with enzymes' secures the process marks.

Key terms to connect with this topic

Use these definitions inside explanations and questions rather than memorising them as isolated sentences.

  • Cloning: The process of producing genetically identical copies of an organism, cell or gene. In plants, cloning can occur naturally through asexual reproduction or artificially through tissue culture (using small pieces of plant tissue grown on nutrient agar with hormones).
  • Fermenter: A large container (bioreactor) used for growing microorganisms on a large scale under controlled conditions. Fermenters have inputs for nutrients, air (if aerobic) and monitoring systems for temperature and pH. They are used to produce antibiotics, enzymes, single-cell protein and other biotechnology products.
  • Genetic modification: The process of altering the genetic material of an organism by inserting a gene from a different organism, often from a different species, to give the organism a desired characteristic. Also called genetic engineering. Examples include producing insulin in bacteria and making crops resistant to herbicides or pests.
  • Ligase: An enzyme that joins together two pieces of DNA by forming bonds between the sugar-phosphate backbones. In genetic engineering, DNA ligase is used to seal the desired gene into the plasmid vector after it has been cut by a restriction enzyme.
  • Pasteurisation: A process used to reduce the number of harmful microorganisms in food or drink (especially milk) by heating it to a specific temperature (usually 72 degrees Celsius for 15 seconds) and then rapidly cooling it. This kills most pathogenic bacteria without significantly altering taste or nutritional value.
  • Plasmid: A small circular ring of DNA found in bacterial cells, separate from the main bacterial chromosome. In genetic engineering, plasmids are used as vectors: they are cut open with restriction enzymes, the desired gene is inserted, and the recombinant plasmid is returned to a bacterium.
  • Restriction enzyme: An enzyme that cuts DNA at specific base sequences, producing fragments with either blunt or sticky ends. In genetic engineering, restriction enzymes are used to cut out a desired gene from donor DNA and to cut open a plasmid vector at a corresponding site.
  • Vector: In genetic engineering, a carrier molecule used to transfer a gene from one organism into another. The most common vector is a bacterial plasmid, but viruses can also be used. In disease biology, a vector is an organism (such as a mosquito) that transmits a pathogen from one host to another.

Browse the full IGCSE Biology glossary when a related term needs checking.