Page 4 - 11-Bio-8 Kingdom plantae

8. Fungi The Kingdom of Recyclers eLearn.Punjab

are absorbed back into the fungus. Saprobic fungi anchor to the substrate by modified hyphae,

the rhizoids. Fungi are the principal decomposers of cellulose and lignin, the main components

of plant cell walls (most bacteria cannot break them). Extensive system of fast growing hyphae

provides enormous surface for absorptive mode of nutrition. Saprobic fungi, alongwith bacteria,

are the major decomposers of the biosphere, contributing to the recycling of the elements (C, N, P,

0, H etc) used by living things.

Some fungi are parasites, some are even predators, and still others are mutualists. Parasitic
fungi absorb nutrients directly from the living host cytoplasm with the help of special hyphal tips
called haustoria. They may be obligate or facultative. Obligate parasites can grow only on their
living host and cannot be grown on available defined growth culture medium. Various mildews
and most rust species are obligate parasites. Facultative parasites can grow parasitically on their
host as well as by themselves on artificial growth media.

Some fungi are active predators. The oyster mushroom (Pleurotus ostreatus) is an omnivorous
(predatory) fungus. It paralyses the nematodes (that feed on this fungus), penetrate them, and
absorb their nutritional contents, primarily to fulfil its nitrogen requirements. It fulfills its glucose
requirements by breaking the wood. Some species of Arthrobotrys trap soil nematodes by forming
constricting ring, their hyphae invad and digest the unlucky victim. Other predators have other
adaptations, such as secretion of sticky substances.

Fig 8.2 Carnivorous fungi (a) The osyter mushroom decomposes wood, and also uses nematodes as a source of nitrogen (b) A nematode
is trapped in constricting ring of a soil - dwelling carnivorous fungus (Arthrobotrys sp.).

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