Neutralized activated charcoal in young regenerating cultures is sometimes added to the medium to achieve which purpose(s)?

Introduction / Context:
Activated charcoal (AC) is a high-surface-area adsorbent sometimes included in plant tissue culture media, particularly during regeneration phases. Its use must be intentional because it can significantly change medium chemistry.

Given Data / Assumptions:

• Explants under stress can exude phenolic compounds that oxidize and inhibit growth.
• Carryover or residual PGRs may hinder phase transitions (e.g., from callus to organogenesis).
• Neutralized AC minimizes pH shock but still adsorbs molecules.

Concept / Approach:
AC binds small aromatic and hydrophobic molecules, reducing phytotoxic phenolics and lowering free concentrations of auxins/cytokinins if desired. This can improve morphogenesis quality and reduce browning. It does not directly buffer pH like a designated buffer system.

Step-by-Step Solution:

Verification / Alternative check:
Protocol notes commonly caution that AC may also remove vitamins or other organics, evidencing its broad adsorptive action.

Why Other Options Are Wrong:

• Maintain the pH: AC is not a primary pH buffer.
• Supply micronutrients: not a controlled nutrient source.

Common Pitfalls:
Unintended adsorption of beneficial components (e.g., vitamins, hormones); using AC without adjusting PGR/vitamin levels accordingly.

Final Answer:
Both (a) and (b)