Basic mycology concept: Saprophytic fungi obtain nutrition primarily by which mechanism?

Introduction / Context:
Saprophytic fungi play vital ecological roles as decomposers, recycling complex organic matter into simpler molecules. Unlike phagocytic protozoa, fungi use extracellular digestion coupled with absorption to obtain nutrients.

Given Data / Assumptions:

• The focus is on saprophytes, not parasites or mutualists.
• Fungal cells have rigid cell walls that preclude engulfment (phagocytosis).
• Substrates include leaf litter, wood, and other dead biomass.

Concept / Approach:
Fungi secrete hydrolytic enzymes (cellulases, ligninases, proteases, lipases) into their environment. These enzymes degrade macromolecules into soluble monomers and oligomers that can be absorbed across the fungal cell wall and plasma membrane. This absorptive nutrition is fundamental to fungal biology and ecosystem nutrient cycling.

Step-by-Step Solution:
Contrast fungal cell wall architecture with phagocytic cells: phagocytosis is not typical for fungi. Describe extracellular enzyme secretion onto dead organic matter. Explain absorption of soluble breakdown products across the cell envelope. Identify option describing enzyme secretion and absorption as correct.

Verification / Alternative check:
Wood-decaying basidiomycetes and soil molds exemplify this process by clearing zones on polymer-containing plates (e.g., cellulose) due to extracellular enzyme activity.

Why Other Options Are Wrong:

• Engulfment (a): Incompatible with rigid fungal cell walls.
• Both / None: Incorrect because only absorptive extracellular digestion is accurate.
• Photosynthesis: Fungi lack chloroplasts and chlorophyll.

Common Pitfalls:
Confusing fungal absorptive nutrition with phagocytosis or plant photosynthesis.

Final Answer:
Securing nutrients by secreting enzymes onto dead organic material and absorbing the breakdown products.