Bioprocess Engineering

A production target helps in process planning and control. For exams connect target with production efficiency.

A suitable organism can grow fast and make useful product. For exams connect organism selection with productivity.

At lab scale a process can be tested safely and cheaply. For exams remember it as an early step before scale up.

The distinction is based on the intended function of the medium. Production medium is formulated to support high biomass formation or efficient synthesis of a desired product, so its nutrients and conditions are selected for process output. Maintenance medium is designed to keep a culture viable and stable during storage or routine transfer, often without maximizing product formation. Its purpose is preservation, not necessarily the highest yield. Option A is correct because it identifies these different objectives. Options B and C are false generalizations: media are not necessarily metal and normally provide suitable nutrients. Option D is also false because maintenance medium is not inherently toxic.

Growth factors may be needed for normal growth of some cells. For exams treat them as special nutrients.

Resistant cells can survive in presence of an antibiotic. For exams connect selection with markers.

Working volume is the useful part where culture runs. For exams keep total volume and working volume separate.

Headspace can play a role in gas exchange and foam control. For exams remember it as the space above liquid.

Residence time is the average time for which liquid, culture medium, or cells remain in a bioprocess system, especially in a continuous fermenter. Therefore, option A is correct. The total time needed to complete a batch is not residence time; it refers to the duration of a batch process. Exam tip: In continuous processes, relate residence time to vessel volume and flow rate.

Dilution rate affects cell growth in continuous culture. For exams remember it as a continuous process parameter.

In a chemostat fresh medium enters and culture fluid leaves. For exams remember it as a controlled continuous system.

The direct answer is A: cells can be washed out when too many leave a continuous culture. In a continuous bioreactor, fresh medium enters while an equal volume of culture leaves. The dilution rate is the flow rate divided by the culture volume, often written as the reciprocal of the residence time. If the dilution rate becomes greater than the cells’ effective growth rate, cells cannot reproduce quickly enough to replace the cells leaving. Their concentration falls greatly, and the culture may be lost; this is washout. Option A is correct because it describes this loss of cells from the system. Option B is wrong because giving a fermenter a clean name has no biological meaning. Option C is wrong because washout does not guarantee product purity. Option D is wrong because freezing the medium is a different event and usually stops growth. The exam cue is: continuous culture plus dilution rate higher than growth rate leads to washout.

The governing concept is oxygen transfer in an aerobic bioprocess. Oxygen has limited solubility in aqueous culture medium, so the dissolved oxygen available to cells can fall below their metabolic requirement. When oxygen becomes limiting, cell growth, respiration, and product formation may decrease. Agitation and aeration increase gas–liquid contact and help replenish dissolved oxygen, while sensors can monitor its concentration. Therefore, option A is correct because supplying enough oxygen to aerobic cells may be difficult. Option B concerns physical state, option C is unrelated to oxygen transfer, and option D is not a consequence of oxygen solubility.

More active cells can use more oxygen. For exams remember the relation between growth rate and oxygen demand.

Oxygen and carbon dioxide in exhaust gas can indicate cell activity. For exams connect it with process monitoring.

Cells perform energy conversions during growth which may produce heat. For exams connect temperature control with metabolism.

High temperature can affect enzymes and cells. For exams remember the need for temperature control.

Acidic products can make the medium more acidic. For exams remember relation between product formation and pH change.

A controlled acid addition can reduce alkalinity. For exams understand pH adjustment as controlled process.

Direct answer: Option A is correct. In a bioprocess, a nutrient feed supplies substrate or other nutrients to growing cells, especially in a fed-batch process. The feed rate must match the organism’s ability to use the nutrient and the desired product pathway. If feed is too low, cells may lack nutrients and growth or product formation may slow. If feed is too high, unused substrate may accumulate, unwanted by-products may form, oxygen or heat demand may rise, and the culture may become unbalanced. Therefore an incorrect feed rate can disturb growth or product formation, as option A states. Option B is wrong because a feed rate cannot make a fermenter become new. Option C is too absolute and unsupported; product does not necessarily disappear immediately, although poor feeding can reduce production or cause loss. Option D is impossible because the medium does not become metal. Option A is scientifically cautious because the exact consequence depends on the organism, nutrient and process. Memory cue: fed-batch means controlled feeding; wrong feeding can mean too little growth or too many unwanted effects.

High salts can put water balance pressure on cells. For exams connect osmotic stress with cell growth.

In solid state fermentation available water affects cell growth. For exams connect water activity with solid medium.

When viscosity increases, flow and circulation of the medium may decrease. This weakens mixing and can reduce oxygen transfer from the gas phase to the liquid, so option A is correct. In contrast, a more viscous medium generally requires more energy for agitation, making option C incorrect. Exam tip: associate high viscosity with poor mixing and reduced oxygen transfer.

Delicate animal cells can be damaged easily by shear stress because their cell membranes are fragile. Therefore, bioprocesses for such cells use gentle mixing, suitable agitation, and low-shear conditions. Vigorous mixing produces high shear stress and may reduce cell viability. Exam tip: associate animal-cell culture with low shear and gentle handling.

Some cells need a surface for growth. For exams connect microcarriers with animal cell culture.