Chapter 31: Fungi (life cycles and diagrams)

Question 1

Explain the sexual life cycle of a fungi.

Answer 1

1. A hyphae (n) from one mycelium fuses with the hyphae (n) of another mycelium
2. Plasmogamy occurs
   - cytoplasms of mycelia unite
   - nuclei from each mycelia do not fuse right away (heterokaryotic stage)
3. Karyogamy occurs
   - the haploid nuclei fuse and zygotes (2n) form
4. Meiosis occurs and haploid spores are produced
5. Spores germinate (grow and develop) into a new mycelium

Question 2

Explain the sexual life cycle of Phylum Zygomycota.

Answer 2

1. Neighboring mycelia of different mating types (+/-) form hyphal extensions containing several haploid nuclei
2. Plasmogamy occurs
   - cytoplasms of mycelia unite
   - nuclei do not fuse right away (n) (heterokaryotic stage)
   - zygosporangium (w/ rough wall) forms
3. Karyogamy occurs
   - the haploid nuclei fuse and zygotes (2n) form
4. Meiosis occurs and the zygosporangium (n) germinate into a sporangium on a short stalk
5. Sporangia disperse haploid spores that germinate and grow into new mycelia

Question 3

Explain the sexual life cycle of Phylum Ascomycota.

Answer 3

1. Mycelia produce specialized hyphae, which conidia (asexual spores) fuse to.
2. Plasmogamy occurs
   - cytoplasms of mycelia unite
   - nuclei do not fuse right away (dikaryotic stage)
   - hyphae (2n) produce many asci (2n)
3. Karyogamy occurs
   - the haploid nuclei fuse and zygotes (2n) form
4. Meiosis occurs and 4 haploid nuclei are yielded within one ascus, which then proceeds to mitosis where 8 haploid nuclei are yielded within one ascus
5. The 8 haploid nuclei develop into ascospores
6. The ascospores disperse through an opening in the ascocarp and give rise to new mycelia

Question 4

Explain the sexual life cycle of Phylum Basidiomycota.

Answer 4

1. Two haploid mycelia of different types (+/-) undergo plasmogamy
2. New mycelium forms and gives rise to mushrooms (basidiocarps) as a result of environmental stress
3. Karyogamy occurs
   - in the gills of the mushroom, there are cells called basidia that produce a diploid nucleus
4. Each diploid nucleus yields 4 haploid nuclei per basidium, which develop into basidiospores
5. The basidiospores disperse by the wind when they are mature and germinate into new mycelia