In plant and microbial biotechnology, suspension cultures consist of single cells and small aggregates growing dispersed in which type of medium?

Introduction / Context:
Suspension cultures are widely used in plant tissue culture and microbial bioprocessing for rapid growth, homogenous sampling, and scalable product formation (for example, metabolites, recombinant proteins). Recognizing the correct growth environment is essential for selecting agitation, aeration, and bioreactor configuration.

Given Data / Assumptions:

• Cells are present as discrete single cells or small clumps (aggregates).
• A well-mixed environment is required to keep cells suspended.
• Nutrient and gas transfer must be adequate throughout the culture.
• Shear should be controlled to avoid aggregate disruption or cell damage.

Concept / Approach:
By definition, a “suspension” implies particles freely dispersed in a fluid. In biological suspensions, cells are suspended in a liquid phase, maintained by agitation (shakers, stirrers) and sometimes by baffles or impellers in bioreactors. Solid media (agar plates) support colonies but do not produce cell suspensions; that is a hallmark of liquid systems.

Step-by-Step Solution:
Match the word “suspension” to a fluid phase compatible with mixing. Exclude solid media, which yield colonies rather than suspended cells. Identify liquid medium as the only environment that keeps cells dispersed. Select “liquid medium.”

Verification / Alternative check:
Standard protocols for plant cell suspensions begin with callus on solid media, then transfer friable callus to liquid medium for shake-flask culture—validating the definition.

Why Other Options Are Wrong:

• Solid nutrient medium: Supports colonies, not suspensions.
• Solid or liquid medium: Overbroad; suspension specifically refers to liquid.
• None of these: Incorrect because liquid medium is correct.

Common Pitfalls:
Assuming any medium that supports growth qualifies. “Suspension” specifically denotes dispersed growth in a liquid phase.

Final Answer:
liquid medium.