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ch 31 - BIO EXAM II ch 31 I Fungi Some fungi are...

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BIO EXAM II   ch 31 I) Fungi: Some fungi are single-celled, but most form complex multicellular bodies; are also essential for the well-being of most  terrestrial ecosystems. They break down organic material and recycle nutrients A) fungi are heterotrophs—they cannot make their own food as plants and algae can, but fungi do not ingest (eat) their food.  Instead, they digest their food while it is still in the environment by secreting powerful hydrolytic enzymes, called  exoenzymes into their surroundings. Exoenzymes break down complex molecules to smaller organic compounds that the fungi can absorb  into their bodies and use. B) Among the fungi are species that live as decomposers (also called saprobes), parasites, and mutualistic symbionts.  i) Saprobic fungi break down and absorb nutrients from nonliving organic material, such as fallen logs, animal corpses, and  the wastes of living organisms.  ii) Parasitic fungi absorb nutrients from the cells of living hosts.  iii) Mutualistic fungi also absorb nutrients from a host organism, but the mutualistic fungi reciprocate with functions beneficial  to the host in some way, such as aiding a plant in the uptake of minerals from the soil. C) hyphae     : network of tiny filaments formed by the multicellular bodies  i) hyphae are composed of tubular cell walls surrounding the plasma membrane and cytoplasm of the cells; fungal cell walls  contain  chitin , a strong but flexible nitrogen- containing polysaccharide that is also found in the external skeletons of  insects and other arthropods. ii) Fungal hyphae form an interwoven mass called a  mycelium  (plural,  mycelia ) that surrounds and infiltrates the material on  which the fungus feeds.  (a) maximizes the ratio of its surface area to its volume, making feeding more efficient. (b) Fungal mycelia are nonmotile, But the mycelium makes up for its lack of mobility by swiftly extending the tips of its  hyphae into new territory; fungus concentrates on adding hyphal length (c) hyphae are divided into cells by cross-walls, or  septa generally have pores large enough to allow ribosomes,  mitochondria, and even nuclei to flow from cell to cell (1) Some fungi lack septa. Known as  coenocytic  fungi, these organisms consist of a continuous cytoplasmic mass  containing hundreds or thousands of nuclei (d)
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