Use of Biological Resources · 3 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 7% of your exam marks.
Microorganisms in food production (yeast, yoghurt, fermenter conditions) and glasshouse/fertiliser yield questions recur across most series.
When a useful product (such as the protein insulin from genetically engineered bacteria in topic 18, mycoprotein, or an antibiotic) is made by culturing microorganisms on a large scale, the microorganisms are grown in a large stainless-steel vessel called an . The fermenter must provide and maintain the conditions the microorganisms need to grow quickly and make the product, while keeping unwanted microorganisms out.
| Condition the fermenter provides | Why it is needed | How the fermenter does it |
|---|---|---|
| Aseptic (sterile) conditions | Stop other microorganisms contaminating the culture, competing for nutrients or spoiling the product | The vessel and the nutrient medium are sterilised (e.g. with steam) before use, and only filtered air is let in |
| Nutrient medium | Supply the carbon, nitrogen and mineral ions the microorganisms need to respire and build new cells | A measured supply of nutrients (such as sugars and a nitrogen source) is added |
| Optimum temperature | Enzymes work fastest at the optimum; too hot and they denature, too cold and growth is slow |
When all of these are kept at their best values, the microorganisms multiply rapidly and make large amounts of the product, which is then extracted and purified.
| A water jacket around the vessel removes the heat released by respiration and a temperature probe keeps it steady |
| Optimum pH | Enzymes work best at a particular pH; the wrong pH slows growth | A pH probe monitors the culture and acid or alkali is added automatically to correct it |
| Oxygenation | Aerobic microorganisms need oxygen for respiration to release energy and grow | Sterile air is bubbled in through a sparger at the base |
| Agitation (stirring) | Keeps the microorganisms, nutrients, oxygen and heat evenly distributed so every cell has the conditions it needs | A motor-driven paddle or stirrer mixes the contents continuously |