BSC 314 Lecture Notes - Lecture 49: Nuclear Material, Meiosis, Spindle Apparatus
27 Jun 2018
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Characteristics of Fungi
All fungi have some features in common, but other special structural and reproductive
features separate the four phyla.
Structure
The fungi are eukaryotic and have membrane-bound cellular organelles and nuclei. They have no
plastids of any kind (and no chlorophyll).
The hyphae of the fungi are of two general kinds: Some are septate, and are divided by septa (walls) that
separate the cylindrical hypha into cells; in the nonseptate fungi, the hypha is one long tube. (The septa
are perforated, however, permitting the cytoplasm to flow throughout the length of the filament.) Mitosis
occurs in the nonseptate hyphae, but there is no accompanying cytokinesis (division of the cytoplasm)
so the hyphae are multinucleate (with many nuclei). The special name for this condition—an organism or
part of an organism with many nuclei not separated by walls or membranes—is coenocytic, and the
organism is a coenocyte.
A few fungi—called by the general name yeasts—are single-celled, and nonfilamentous much of the time.
The only flagellated cells in the kingdom are the flagellated gametes of the chytrids.
Metabolism
The fungi are all heterotrophic, but unlike animals and many other heterotrophs thatingest their nutrients
as bits or bites of food, the fungi secrete digestive enzymes into their surroundings, in effect digesting
their food outside of their bodies. They then canabsorb the smaller particles and incorporate the nutrients
into their own cells. Some areparasites obtaining nutrients from living organisms, but more are saprobes
(saprotrophs) that digest and recycle materials from dead organisms.
In addition to potent digestive enzymes, some fungi manufacture powerful alkaloids that, when ingested
by humans, assail the nervous system, causing hallucinations and even death. The “death
angel,” Amanita, is one such well-known poisonous fungus; ergot ( Claviceps purpurea) is another.
Fungal hyphae, like the roots of vascular plants, grow primarily at the tip, elongating and branching
repeatedly. The filaments are in direct contact with their environment, obviating in the fungal body the
need for separate absorbing and conducting systems (and precluding the need for storage tissues).
Materials readily pass through the plasma membrane and cell walls of the hyphae along their entire
length, although the most active metabolism and material exchange is concentrated near the hyphal tips.
Most of the cytoplasm is located at the tips also.
Fungi: Reproduction
Nonmotile sexual and asexual spores—microscopic in size—are the common means of
reproduction and the primary agents of fungal dispersal. They are readily carried in air
or attached to the bodies of insects and other animals and are not resistant structures
like bacterial endospores. Although they can withstand desiccation, they are killed by
heat. Sexual spores often require a period of dormancy after they are formed, but
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