What it shows
To make a product with microbes (an enzyme, an antibiotic, or human insulin from recombinant bacteria) you need billions of cells, grown in large bioreactors. The most common is the stirred tank: a steel vessel with a stirrer, an air pipe (sparger) bubbling air in at the bottom, a cooling jacket, probes that measure temperature, pH and dissolved oxygen, and pumps that add acid or base.
Growing cells keep pushing the tank away from the best conditions: they give off heat, they make acid, and they use up oxygen. Each of these has a control loop: a probe measures the value, and the controller acts (more cooling water, a little base, a faster stirrer) to pull it back to its set point.
This page simulates a 24-hour batch of bacteria on 20 g/L of sugar. Switch each loop off to see what it was doing.
It fits Class 12 Biology: biotechnology, principles and processes (obtaining the foreign gene product: bioreactors, the stirred-tank reactor, downstream processing) and microbes in human welfare (industrial products). The cells being grown might carry the gene from recombinant insulin; their growth curve is the logistic shape in population growth, and why temperature and pH matter so much is shown in enzyme activity lab.
How to use it
- Leave all three loops on, then switch one off at a time.
- Slide the set points: temperature, pH and the oxygen level to keep above. With oxygen control off, set the fixed stirring instead.
- Drag the Hour slider: the gauges by the tank show the values at that hour, and the sentence says what is wrong, if anything.
- Read the growth graph and the facts: bacteria at 24 h, when the sugar runs out, and the highest temperature, lowest pH and lowest oxygen.
Worked example
With every loop on (37 °C, pH 7, oxygen above 30 %), the bacteria grow from 0.1 to 10.1 g/L and use up the sugar after about 9.7 hours: 20 g/L of sugar × 0.5 g of cells per gram of sugar = 10 g/L of new cells. The temperature never goes above 37.8 °C and the pH never below 6.85.
Switch temperature control off and the tank heats up to about 44.9 °C; growth slows and sugar is still left after 24 hours. Switch pH control off and the acid takes the pH down to about 5.64, with 9.15 g/L of bacteria. Switch oxygen control off with fixed stirring 2 per hour, and the oxygen falls to about 2.8 %: the cells still finish, but only after about 14.4 hours.
Check yourself
Five fresh questions: cells from sugar using the yield, kilograms in a tank, and why tanks are cooled, stirred and followed by downstream processing. Nothing is saved.
FAQ
Why not just grow cells in a flask? Flasks work for small amounts. A bioreactor keeps conditions right for thousands of litres, keeps the culture sterile, and lets samples be taken.
What happens after the batch? Downstream processing: the product is separated from the cells and broth, purified, tested for quality, and formulated with preservatives before it can be used.
Is this from my textbook? It covers the standard school topic with its own model and examples. It is an independent study aid.
Where the numbers come from
- Standard school biotechnology: stirred-tank bioreactors (agitator, sparger, temperature and pH control, sampling) and downstream processing. Growth follows the Monod equation with yield on sugar; temperature, pH and oxygen effects and the simple proportional control loops are teaching choices. Written for fibub; no textbook text, figures or exercises are used.
- All numbers (growth rate, yield, heat, acid and oxygen per gram of growth, the best temperature 37 °C and pH 7) are round, made-up teaching values, not data for any real organism.
- Checked against scipy.integrate.solve_ivp (LSODA, rtol 1e-10) on the same equations at 6 and 12 hours, with all loops on and with each switched off.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.