1. Systematic Position
Kingdom: Fungi
Division: Eumycota
Subdivision: Zygomycotina
Class: Zygomycetes
Order: Mucorales
Genus: Rhizopus
👉 Commonly known as black bread mould.
2. Habitat
Saprophytic fungus
Grows on bread, fruits, vegetables, damp organic matter
Cosmopolitan in distribution (common in warm, humid conditions)
3. Thallus Structure
Body consists of well-developed mycelium
Mycelium is:
Aseptate (coenocytic)
Multinucleate
Hyphae are differentiated into three types:
(a) Stolons
Horizontal hyphae spreading over substratum
Help in vegetative propagation
(b) Rhizoids
Root-like hyphae penetrating the substratum
Function: absorption and anchorage
(c) Sporangiophores
Upright aerial hyphae
Bear sporangia at their tips
4. Cell Wall & Protoplasm
Cell wall made of chitin + chitosan
Cytoplasm contains:
Multiple nuclei
Mitochondria
Vacuoles
Oil droplets (reserve food)
5. Nutrition
Mode of nutrition: Saprophytic
Feeds on dead organic matter by:
Secreting extracellular enzymes
Absorbing soluble nutrients
6. Reproduction in Rhizopus
Occurs by three methods:
A. Vegetative Reproduction
By fragmentation of mycelium
Each fragment grows into a new mycelium
B. Asexual Reproduction
Occurs by sporangiospores
Sporangium Structure
Spherical, black in color
Wall encloses many non-motile spores
Central sterile dome-shaped structure → Columella
Process
Sporangiophore develops at the node opposite rhizoids
Tip swells to form sporangium
Cytoplasm divides into many spores
Sporangium ruptures → spores released
Each spore germinates into new mycelium
C. Sexual Reproduction
Type: Gametangial copulation
Condition: Unfavourable conditions
Process
Two compatible hyphae (+ and – strains) come close
Terminal parts swell → progametangia
Septa form → gametangia
Fusion of cytoplasm (plasmogamy)
Fusion of nuclei (karyogamy)
Formation of thick-walled zygospore
Zygospore
Dark, thick-walled
Resting structure
Germinates after dormancy to form a sporangiophore
7. Life Cycle
Haploid dominant
Diploid phase restricted to zygospore nucleus
8. Economic Importance
Harmful Effects
Spoilage of bread and fruits
Causes soft rot in vegetables
Useful Aspects
Used in production of organic acids
Important decomposer in ecosystem
9. Diagnostic Features (Exam Points)
Aseptate coenocytic mycelium
Presence of stolons, rhizoids & sporangiophores
Asexual reproduction by sporangiospores
Sexual reproduction by zygospore formation
