Summary
Contents
Fungi are eukaryotic organisms that appeared on land more than 450 million years ago. They are heterotrophs and contain neither photosynthetic pigments such as chlorophyll, nor organelles such as chloroplasts. Because fungi feed on decaying and dead matter, they are saprobes. Fungi are important decomposers that release essential elements into the environment. External enzymes digest nutrients that are absorbed by the body of the fungus, which is called a thallus. A thick cell wall made of chitin surrounds the cell. Fungi can be unicellular as yeasts, or develop a network of filaments called a mycelium, which is often described as mold. Most species multiply by asexual and sexual reproductive cycles and display an alternation of generations. Another group of fungi do not have a sexual cycle. Sexual reproduction involves plasmogamy (the fusion of the cytoplasm), followed by karyogamy (the fusion of nuclei). Meiosis regenerates haploid individuals, resulting in haploid spores.
Glossary
coenocytic hypha
single hypha that lacks septa and contains many nuclei
faculative anaerobes
organisms that can perform both aerobic and anaerobic respiration and can survive in oxygen-rich and oxygen-poor environment
haustoria
modified hyphae on many parasitic fungi that penetrate the tissues of their hosts, release digestive enzymes, and/or absorb nutrients from the host
heterothallic
describes when only one mating type is present in an individual mycelium
homothallic
describes when both mating types are present in mycelium
hypha
fungal filament composed of one or more cells
karyogamy
fusion of nuclei
mycelium
mass of fungal hyphae
mycology
scientific study of fungi
obligate aerobes
organisms, such as humans, that must perform aerobic respiration to survive
obligate anaerobes
organisms that only perform anaerobic respiration and often cannot survive in the presence of oxygen
plasmogamy
fusion of cytoplasm
saprobe
organism that derives nutrients from decaying organic matter; also saprophyte
septa
cell wall division between hyphae
sporangium
reproductive sac that contains spores
thallus
vegetative body of a fungus
yeast
general term used to describe unicellular fungi