Bioprocess Engineering

A suitable strain can give more stable product output. For exams connect strain selection with production efficiency.

Seed culture provides active cells to start the main process. For exams remember it as inoculum preparation.

The governing concept is aseptic processing and contamination prevention. Aerobic cultures require air, but untreated incoming air can carry bacteria, fungal spores or other unwanted organisms. A suitable air filter removes or retains these contaminants before the air enters the fermenter, helping maintain a sterile or low-contamination environment. Therefore option C is correct. The filter does not sweeten the medium, freeze the product or colour the vessel. Sterile air is especially important when the desired production organism must grow without competition and when the product must meet quality and safety requirements. Filtration supports sterility, although it works together with sanitation, sterilisation and controlled operation.

Baffles reduce unwanted vortex and improve mixing. For exams connect baffles with mixing control.

A cooling jacket removes excess heat and controls temperature. For exams remember it as a temperature control device.

A sampling port allows clean collection of culture samples. For exams connect it with process monitoring.

A pressure gauge helps in safe operation of the system. For exams connect it with safety and control.

An exhaust gas line removes gases from a fermenter in a controlled way. For exams remember it as part of the aeration system.

The direct answer is A: the amount of oxygen dissolved in the medium. A dissolved oxygen, or DO, probe detects oxygen available in the liquid phase of a bioreactor, usually as a concentration or percentage of air saturation. This is important because aerobic cells need oxygen for respiration and growth. The probe sends a signal to the control system, which may adjust stirring or air supply when oxygen becomes too low. Option A is correct because it states exactly what the probe measures. Option B is wrong: fermenter height is measured by physical dimensions or a level instrument, not a DO probe. Option C is wrong: the product name is recorded as information and cannot be measured by this sensor. Option D is wrong: sound is measured by an acoustic instrument, not by an oxygen probe. A helpful exam cue is to connect DO with aerobic culture, aeration, and agitation; it is not a measurement of vessel size or product identity.

A pH probe shows acidity level and helps control it. For exams connect pH with enzyme activity.

Optimized medium gives proper nutrients and can increase yield. For exams connect medium optimization with better production.

A substrate is used by cells and helps product formation. For exams remember it as raw material.

Some products can slow the process when present in high amount. For exams remember it as a yield control problem.

Immobilized cells remain attached to a support and can be reused. For exams connect it with cost reduction.

An immobilized enzyme is attached to a support and can be used many times. For exams connect it with industrial enzyme use.

In a packed bed liquid can pass through immobilized biological material. For exams connect it with immobilized enzyme processes.

In an airlift bioreactor air moves the liquid up and down. For exams remember it as a system with lower mechanical damage.

A stirred tank uses an impeller for mixing and oxygen distribution. For exams remember it as a common industrial bioreactor.

High shear stress can break delicate cells. For exams remember the balance between mixing and cell safety.

A control system keeps conditions such as temperature and pH stable. For exams connect it with safe and consistent production.

In lag phase cells adapt before active growth. For exams consider it the initial preparation phase.

In exponential phase cells divide rapidly. For exams remember it as the highly active growth phase.

In stationary phase new cell formation and death may nearly balance. For exams remember nutrient limitation as a reason.

In death phase living cells decrease due to unfavorable conditions. For exams remember it as the final part of the growth curve.

Cell viability is the proportion or percentage of living cells in a cell population. Only viable cells can grow and contribute to the formation of the desired biological product. The rate of product formation may be affected by viability, but it is not the definition of viability. Exam tip: associate viability with the percentage of living cells.