Bioprocess Engineering

Pure culture reduces the effect of unwanted microbes. For exams connect pure culture with correct product formation.

Starter culture is added to begin the production process. For exams connect it with the idea of inoculum.

Mineral salts support enzyme activities and cell growth. For exams remember the role of micronutrients.

The governing concept is pH buffering. A buffer contains a weak acid and its conjugate base, or a related chemical pair, that can absorb limited additions of acid or alkali and thereby resist sudden pH changes. Microbial metabolism often produces acidic or basic substances, so an uncontrolled culture may move away from the pH needed for growth, enzyme activity and product formation. Option D is correct because the buffer keeps pH relatively stable, though it does not hold it perfectly constant under unlimited disturbance. It is not primarily a killing agent, a sweetener or a material for converting product into metal. Larger pH corrections may still require controlled addition of acid or base.

Stainless steel is useful for cleanliness and durability. For exams connect fermenter material with industrial cleaning.

A HEPA filter is designed to remove a very high proportion of airborne particles from a stream of air. In a bioprocess, clean air is important because unwanted dust and microorganisms can contaminate the culture, medium or equipment. Air supplied to a fermenter or other controlled processing area may therefore pass through suitable high-efficiency filtration before use. This supports aseptic or low-contamination operation. A HEPA filter does not freeze a medium, colour a product or cut a fermenter. Consequently, option B, removing fine particles and microbes from air, is the correct choice.

The reasoning depends on the material being filtered: HEPA equipment is an air filter, not a cooling, colouring or cutting device. It traps airborne particles, including many particles carrying microorganisms, and helps provide cleaner process air. It should not be confused with a guarantee that every system is completely sterile; proper sterilisation and aseptic practices may also be needed. For the school-level question, however, its recognised use is supplying filtered, clean or sterile air in bioprocessing. The supplied answer B and its explanation are scientifically appropriate.

A laminar air flow cabinet supplies HEPA-filtered clean air in a uniform direction, reducing contamination by airborne microorganisms and dust in the work area. Hence, its main advantage is enabling aseptic handling of cultures and media. Boiling a medium is a separate sterilisation procedure. Exam tip: associate a laminar air flow cabinet with aseptic transfer and contamination control.

A culture bank preserves good strains for future use. For exams connect it with strain preservation.

A master cell bank is a stable source of cells with consistent quality. For exams remember it as a standardized cell source.

A working cell bank is a source of cells for repeated production use. For exams understand it as a practical stock derived from the master cell bank.

Low inoculum can slow the start of growth. For exams connect inoculum amount with process time.

An old culture may have reduced cell viability. For exams connect inoculum age with active growth.

In some processes limited nutrients influence product formation. For exams connect nutrient control with production control.

Excess substrate is not always beneficial because it can affect the process. For exams remember balanced feeding.

Mass transfer helps oxygen and nutrients reach cells. For exams connect it with mixing and aeration.

Aerobic microbes need enough oxygen. For exams connect oxygen transfer with aerobic production.

Gas removal keeps internal conditions controlled. For exams connect exhaust gas with process control.

The governing concept is pH regulation in a biological culture. Acids release hydrogen ions and generally lower pH, whereas alkalis neutralize acidity and generally raise pH. During fermentation, microbial metabolism can change the acidity of the medium, so sensors and a control system may add acid or base to keep pH within the range required for growth, enzyme activity and product formation. Option B is therefore correct. Temperature control uses heating or cooling, pressure control changes vessel pressure, and light control concerns illumination; none is identified by adding acid or alkali. The addition must be gradual and monitored because an excessive dose can create local pH shock or harm cells.

Proteins and air bubbles can form foam. For exams connect foam with aeration and medium composition.

The direct answer is A, oxygen transfer may be affected. Antifoam is added to reduce or control foam in a fermenter, because excessive foam can cause contamination, blocked filters, loss of culture and operating problems. However, an excessive amount is not automatically harmless. Step by step: antifoam spreads at the liquid surface and breaks bubbles; too much may change surface properties, reduce gas-liquid contact area or alter mixing and mass transfer; oxygen may then move less efficiently from air into the culture; microorganisms may receive less dissolved oxygen, so growth or product formation can suffer. Option A is correct because excessive antifoam can reduce oxygen transfer in some systems. Option B, the fermenter always becoming bigger, is not a normal physical consequence. Option C, changing microbe names, is unrelated to antifoam chemistry. Option D, the product becoming glass, is also unrelated and is not a general outcome. The exact effect depends on antifoam type, dose and organism, so ‘may’ is important. Memory cue: antifoam controls bubbles, but too much can interfere with oxygen transfer.

Computer control helps keep conditions such as temperature and pH stable. For exams remember it as automated control.

Temperature is an important controlled parameter in a bioprocess. For exams consider temperature pH and oxygen as key parameters.

Online monitoring means observing and measuring important conditions while a bioprocess is actually running. Sensors or other measuring devices can record values such as temperature, pH, dissolved oxygen, pressure, or the amount of a substance at the required time. The purpose is not merely to collect information, but to notice changes early and support suitable control of the process.

Option D is correct because it directly describes continuous measurement during the process. Guessing later from memory cannot provide reliable real-time information, selling the product is a later business activity, and giving a fermenter an internet name has no connection with monitoring. Online monitoring helps the operator respond promptly if a value moves away from the desired range, improving consistency and safety.

In offline testing a sample is analyzed separately. For exams distinguish it from online monitoring.

Calibration helps sensors and instruments give reliable measurements. For exams connect it with quality control.