Topic 21.1 · Core + Supplement
Why Bacteria Are Used in Biotechnology
It’s tempting to answer this with “bacteria are small and easy to grow,” and that answer will not earn the mark. Cambridge wants two named Core reasons, and Supplement candidates need two more on top — each one a distinct, separately assessable point.
Biotechnologyis the use of living organisms, or products made by them, to manufacture useful goods for people. That definition matters here because it doesn’t require genetic modification at all — bread-making is biotechnology even though the yeast in it hasn’t been genetically modified. Bacteria happen to be particularly well suited to this broader field, and the reasons why are specific enough that Cambridge examines them directly.
The two Core reasons
Rapid reproduction.Bacteria reproduce very quickly when conditions are suitable, so a small starting population can become a large population of producer cells in a short time. That matters industrially because if each bacterial cell is producing a useful substance, a large population produces a correspondingly large quantity of it — the route from a small starting culture to a factory-scale yield runs through hours, not months.
Ability to synthesise complex molecules.Bacterial cells can make complex biological molecules, including proteins. That means bacteria aren’t only useful as bacterial cells in their own right — they can be turned into biological production systems for a protein that was never naturally theirs, most importantly a protein made from a gene inserted into them. This is the property that makes the insulin-producing bacteria described in genetic modification: definition and examples possible in the first place.
The two Supplement reasons
Few ethical concerns.Manipulating and growing bacteria raises relatively few ethical concerns compared with using more complex organisms such as animals — but “few” is not “none,” and an answer that rewrites this as “no ethical concerns” has overstated what the syllabus actually says. This comparative ease is part of why it’s practical to grow and genetically modify very large bacterial populations.
Plasmids.A plasmid is a small circular piece of DNA found in bacterial cells, separate from the main bacterial chromosome. Plasmids matter because they can be removed from bacteria, cut, combined with another piece of DNA, and placed back into bacteria — which makes a plasmid an effective way of carrying a required gene into a bacterial cell. Without a plasmid, or another carrier like it, there’s no practical route for new genetic material to get into the bacterium at all. The full mechanics of how that carrying actually works are covered in the process of genetic modification.
Keep the four reasons separate
These four points solve four different practical problems, and an exam answer that blurs them into one vague statement — “bacteria are useful because they’re small and reproduce” — loses marks that a precise answer would keep. Rapid reproduction is about speed and scale. Complex-molecule synthesis is about what the cells can actually build once they’re grown. Plasmids are about how a gene gets into the cell in the first place. Few ethical concerns is about why bacteria are a practically convenient choice compared with growing and modifying animals. Four separate ideas, four separate marks.
Where this leads next
Rapidly-reproducing bacteria still need somewhere to be grown at industrial scale, which is exactly what fermenters and controlled conditionscovers. And a plasmid on its own doesn’t do anything until a gene has actually been cut, inserted and joined into it — the ordered sequence for that is covered in the process of genetic modification.