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Difficulty: MediumKingdom Fungi: Moulds, Yeasts, and Mushrooms

During an observation of mold growth on a slice of damp bread, a student identifies a network of hyphae secreting enzymes onto the bread substrate. Which feature of this fungal organism accounts for its heterotrophic mode of nutrition?

  1. Absence of chloroplasts and reliance on extracellular enzymatic digestionAnswer
  2. B
    Ingestion of insoluble starch particles through specialized rhizoidal pores
  3. C
    Synthesis of organic compounds from inorganic salts via rhizoidal rootlets
  4. D
    Presence of a chitinous cell wall that traps light energy for dark reactions

Answer

The absence of chloroplasts and reliance on extracellular enzymatic digestion accounts for the heterotrophic mode of nutrition in fungi.
Fungi are non-photosynthetic organisms because their cells lack chloroplasts and photosynthetic pigments. As saprophytes, they release digestive enzymes externally onto organic substrates to break down complex molecules into simple dissolved nutrients, which are then absorbed across their cell membranes.

Step-by-Step Solution

1
Identify the nutritional class of fungi
Fungi belong to Kingdom Fungi and are non-photosynthetic heterotrophs (specifically saprophytes when feeding on dead organic matter).
Fungal cells lack chlorophyll and chloroplasts, rendering them incapable of autotrophic food synthesis.
2
Analyze the fungal digestive mechanism
Hyphae secrete hydrolytic enzymes (such as amylases and proteases) onto the surrounding substrate to digest complex organic compounds externally into simple soluble forms.
Extracellular digestion breaks down insoluble food before absorption across the chitinous cell wall and plasma membrane.

Key Concept

Saprophytic Nutrition in Fungi
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Topics

Kingdom Fungi: Moulds, Yeasts, and Mushrooms

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