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Biology for Advanced Level Secondary Schools

and foods. Most ascomycetes have highly spores called ascospores. These spores
branched hyphae. They are multicellular can germinate to form new haploid
except yeasts, which are unicellular. hyphae.

(d) They possess conidia which are
Yeast shows a number of differences in
morphology, reproduction, and cell structure, found at the apex of hyphae called
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when compared to other ascomycetes. conidiophores, which produce millions
Besides lacking hyphae, yeast does not of resistant spores that are used in
have ascocarp, hence they are sometimes asexual reproduction.
referred to as hemiascomycetes; meaning (e) Sexual reproduction is accomplished by
“half ascomycetes,” to distinguish them mating of compatible hyphae forming a
from euascomycetes or true ascomycetes dikaryotic hyphae; that is hyphae with
that have hyphae and ascocarp. They two nuclei in their cell. The nuclei will
extracellularly secrete and produce enzymes fuse only after the formation of ascus.
such as protease (protein digesting enzymes) The diploid nucleus will later undergo
and cellulase (cellulose digesting enzyme). meiotic and mitotic divisions to form
These kinds of enzymes make this group ascospores.
very destructive to animals, and plants.
However, some ascomycetes such as yeast (f) Some ascomycetes such as yeasts
are widely used in brewing industries for are unicellular and they reproduce
production of alcohol through fermentation, asexually by budding (new cells form
while others are used in bakery and textile on the surface of the old ones).
industries.
Distinctive features of phylum

General characteristics of phylum Ascomycota
Ascomycota The following are the distinctive features
of the phylum Ascomycota:
(a) Their mycelium is made up of tightly (a) They have specialised spore producing
woven septate hyphae, except yeasts, structures called ascocarps.
which are unicellular.
(b) They reproduce asexually using conidia
(b) They are heterotrophic saprophytes; formed on the tips of conidiophores; in
in contrast to other members that some members asexual reproduction is
are parasites. For example, Candida through budding.
albicans is an infectious ascomycetes,
which causes mouth thrush. In plants, (c) Some are unicellular heterotrophs, and
they are responsible for powdery they lack typical hyphae, for example
mildews which infects cereal grains. Saccharomyces.

(c) They have a fruiting body containing Structure of Saccharomyces
several sac-like structures called asci Saccharomyces are flat, smooth, and
(singular ascus), which produce haploid

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