In animal cell culture, which statements correctly describe how gas bubbles can damage delicate cells during aeration and mixing?

Introduction:
Animal cells lack a rigid cell wall and are highly sensitive to hydrodynamic and interfacial stresses. Aeration is essential for oxygen supply, yet bubbles and foam can harm cells through several mechanical mechanisms. Understanding these mechanisms guides the selection of sparging strategies, impeller design, and protective additives.

Given Data / Assumptions:

• Cells are shear-sensitive and adhere to interfaces.
• Aeration creates bubbles and potentially foam at the gas–liquid surface.
• Interfaces can concentrate cells and expose them to rupture forces upon bubble breakage.

Concept / Approach:
When bubbles rise and burst at the surface, the rapid retraction of the liquid film and the release of surface energy produce strong micro-eddies and capillary forces. Cells attached to bubble surfaces can experience membrane rupture. In foams, cells entrained between bubbles can be stretched or compressed as bubbles move and coalesce, creating mechanical damage.

Step-by-Step Solution:
Step 1: Identify bubble surface attachment as a risk factor for cell damage.Step 2: Recognize that bubble bursting at the gas–liquid interface releases localized energy that can disrupt membranes.Step 3: Account for foam dynamics, where cells are dragged and deformed by moving bubbles.Step 4: Conclude that both mechanisms in (a) and (b) are valid contributors to damage.

Verification / Alternative check:
Empirical studies report improved viability when bubble exposure is reduced via micro-spargers, membrane oxygenation, or by adding shear protectants that reduce interfacial adsorption of cells.

Why Other Options Are Wrong:

• UV radiation release: Physically incorrect; bubble collapse does not emit ultraviolet radiation.
• Selective lysis of only dead cells: Bubble-related damage is not selective; viable cells are also at risk.

Common Pitfalls:
Assuming that only bulk shear damages cells while ignoring interfacial stresses, or believing that higher airflow always increases oxygen transfer without considering viability loss due to foam and bursting bubbles.

Final Answer:
Both (a) and (b)