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Difficulty: EasyKingdom Fungi: Moulds, Yeasts, and Mushrooms

Arrange the following stages of sexual reproduction (zygospore formation) in the bread mould *Rhizopus* in the correct chronological sequence from start to finish:

  1. 1Hyphae of opposite mating strains (+ and -) make physical contact.
  2. 2Progametangia develop as lateral swellings at the point of contact.
  3. 3Septa form to cut off multinucleate gametangia from the supporting hyphae.
  4. 4The wall between gametangia dissolves, allowing nuclear fusion to form a resistant zygospore.

Answer

The correct chronological sequence of zygospore formation in Rhizopus begins with hyphae of opposite mating strains making contact, followed by the development of progametangia, then the formation of septa to isolate gametangia, and culminates in the dissolution of intervening walls to allow nuclear fusion into a thick-walled zygospore.
Zygospore formation in *Rhizopus* follows a strict sequence: contact between compatible (+ and -) hyphae occurs first, inducing progametangia outgrowth, followed by septum formation to isolate multinucleate gametangia, and ending with wall dissolution and nuclear fusion to produce the mature zygospore.

Step-by-Step Solution

1
Identify the initial stimulus for sexual reproduction.
Hyphae of opposite mating strains (+ and -) grow towards each other and make physical contact.
Physical interaction between compatible mating strains initiates the sexual pathway in mucoralean fungi.
2
Determine the early morphological response to hyphal contact.
Progametangia form as lateral, swollen outgrowths.
Hormonal signaling causes the hyphal tips at the contact zone to swell.
3
Identify the cellular isolation step.
Cross-walls (septa) form behind the tips, delimiting gametangia.
Septa isolate the apical multinucleate gametangia from the rest of the hyphae (suspensors).
4
Determine the final cell fusion and spore maturation event.
The touching walls dissolve, cytoplasm and nuclei fuse, and a thick, dark wall surrounds the resulting zygospore.
Plasmogamy and karyogamy yield a diploid zygospore capable of enduring harsh environmental conditions.

Key Concept

Sexual Reproduction and Zygospore Formation in Rhizopus
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Topics

Kingdom Fungi: Moulds, Yeasts, and Mushrooms

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