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How do factories grow microorganisms in huge tanks and keep the conditions perfect for making a product?

Describe the use of a bioreactor (fermenter) for large-scale culture and the conditions it controls

A focused answer to the O-Level outcome on bioreactors. The parts of a fermenter, the conditions it controls, batch versus continuous culture, and calculating product yield.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this dot point is asking

This outcome asks you to describe a bioreactor (fermenter) for large-scale culture and the conditions it controls. It is where the laboratory techniques scale up to industry: the same growth conditions you met for microbial cultures, now controlled precisely in a large vessel. Examiners reward each condition paired with its reason.

The answer

What a bioreactor is

A bioreactor, or fermenter, is a large vessel in which microorganisms (or cells) are grown under carefully controlled conditions to make a useful product such as insulin, an antibiotic, an enzyme or ethanol.

The conditions it controls

To grow the microorganisms well and maximise the product, a bioreactor controls:

  • Temperature. Kept at the optimum for the microorganisms' enzymes; a water jacket or cooling coils remove the heat released by respiration to prevent overheating.
  • pH. Monitored and adjusted to stay near the optimum, because enzymes are sensitive to acidity and microbial activity can change the pH.
  • Oxygen. Sterile air is bubbled in for aerobic microorganisms, which need oxygen for aerobic respiration.
  • Stirring. A stirrer keeps cells, nutrients and oxygen evenly mixed and in contact.
  • Nutrients. Supplied as food so the microorganisms can grow and make the product.
  • Sterility. The whole vessel and its contents are sterilised first and kept free of contaminating microorganisms.

Batch versus continuous culture

  • Batch culture. A fixed amount of nutrients and microorganisms is added at the start, grown, and the product harvested all at once; then the vessel is cleaned and restarted. It is easier to keep sterile and manage, and a contaminated batch can simply be discarded.
  • Continuous culture. Fresh nutrients are added and product (with some culture) removed continuously, so growth does not stop. This keeps the cells in their productive phase and gives a steady supply, which can be more efficient.

Harvesting

When enough product has formed, it is removed from the vessel and purified.

Examples in context

Example 1. Industrial insulin. Engineered bacteria carrying the insulin gene are grown in large bioreactors with tightly controlled temperature, pH, oxygen and nutrients, all kept sterile, so they produce insulin in bulk. The fermenter is what turns a single transformed cell into a commercial supply.

Example 2. Antibiotic production. Penicillin is made by growing a mould in a large fermenter, with conditions controlled to maximise how much antibiotic the mould produces. It shows the same controlled-culture principle applied to a fungus rather than a bacterium.

Try this

Q1. State three conditions controlled inside a bioreactor. [3 marks]

  • Cue. Temperature, pH and oxygen (stirring, nutrients and sterility are also acceptable).

Q2. Explain why a large fermenter often needs cooling. [2 marks]

  • Cue. The microorganisms release heat during respiration, so cooling removes this heat to keep the temperature at the optimum and prevent overheating.

Q3. A fermenter makes 30 kg30\ \text{kg} of product from 500 kg500\ \text{kg} of sugar. Calculate the percentage yield. [2 marks]

  • Cue. 30500×100=6%\dfrac{30}{500} \times 100 = 6\%.

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original6 marksDescribe the conditions that are controlled inside a bioreactor (fermenter) when growing microorganisms, and explain why each is important.
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Examiners want the controlled conditions, each with a reason linked to growth or product.

Temperature is controlled (often using a water jacket or cooling coils) because the microorganisms' enzymes work best at a particular temperature, and respiration releases heat that must be removed to stop overheating.

pH is monitored and adjusted because enzymes are sensitive to acidity, and the microorganisms' activity can change the pH, so it must be kept near the optimum.

Oxygen is supplied by bubbling in sterile air for aerobic microorganisms, because they need it for aerobic respiration. The contents are stirred to keep cells, nutrients and oxygen evenly mixed and in contact.

Nutrients are supplied so the microorganisms have food to grow and make the product, and the whole vessel is kept sterile to prevent contamination.

What markers reward: temperature (enzymes and removing heat), pH (enzymes, keeping near optimum), oxygen (aerobic respiration) with stirring to mix, nutrients (food), and sterility (no contamination), each with a correct reason.

Original5 marksExplain the difference between batch culture and continuous culture in a bioreactor, giving one advantage of each.
Show worked answer →

The answer should contrast the two methods and give an advantage of each.

In batch culture, a fixed amount of nutrients and microorganisms is added to the fermenter at the start, the culture is grown, and the product is harvested all at once at the end before the vessel is cleaned and restarted. An advantage is that it is easier to keep sterile and to manage, and a contaminated batch can be discarded without affecting others.

In continuous culture, fresh nutrients are added and product (with some culture) is removed continuously while the culture keeps growing, so it does not stop. An advantage is that it keeps the microorganisms in the productive growth phase and gives a steady, ongoing supply of product, which can be more efficient.

What markers reward: batch as a fixed amount grown and harvested all at once then restarted, continuous as constant addition of nutrients and removal of product, with a valid advantage of each (batch easier to keep sterile and manage; continuous steady output and cells kept productive).

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