Chapter 18Fungus

18.1 Fungi are adapted for nutrition by absorption

hyphae: tiny threads of cytoplasm surrounded by a plasma membrane and covered by a cell wallCell walls made of chitin– Strong , flexible

polysaccharide

Cross-walls: divide the long filaments into many cells – Exchange cytoplasm,

organelles and distribute nutrients

Mycelium

mycelium(mycelia): interwoven mat of hyphae–Feeding structure–Maximizes surface area within food–Km of hyphae each day– In Oregon, mycelium is 5.5 km

across, 9 km2 of forest, 2400 years old

Nutrition

absorptive nutrition: method by which the fungus absorbs small organic molecules from its surroundings– Digests food outside mycelium by secreting

enzymes– Enzymes break down molecules so they can be

absorbed

Food sources– Fallen logs, dead animals, waste– Parasitic fungi: absorb nutrients from living hosts

Reproduction

spores: haploid single cells with thick cell walls – Spread by wind and can withstand unfavorable

conditions– Most are asexual– Sexual reproduction: haploid hyphae from

different mycelia fuse together and combine genetic info

Can produce trillions of spores– Puffballs– Found 200 km above the surface

18.2 Kingdom Fungi consists of diverse forms

Zygote Fungi Mostly terrestrial and live in soil or decaying materialRhizopus stolonifer Food available= asexual reprod.– Sporangia: spore-forming structures at tips of hyphae

Food depleted= sexual– Two mycelia fuse– zygosporangium: reproductive structure

Sac Fungi

Marine, freshwater, and terrestrial

Single-celled or large morels

Ascus (sac) contains spores

Similar reproduction to zygote fungus

Club Fungi

Agaricus bisporus – Most common

Important decomposers of wood and plant material– Some are parasites

Usually sexual– Spores drop from

“gills” underneath– Can grow within hours

Club Fungi Reproduction

YeastSingle-celled fungiInhabit liquid or moist habitats– Plant sap and animal tissues

Reproduce asexually – Cell division or pinching of “buds”

Some sexually – Form ascus or basidium; classified as sac or club– Imperfect fungi: no known sexual stage of

reproduction

Used for fermentation or raise dough

MoldAny fungus that grows very rapidly on a surface

Most asexual

Some imperfect

Sexual stages place some in zygote, sac, or club

Rhizopus - zygote

Penicillium - sac

Mmmmm…. cheesy

18.3 Fungi have a major impact on other life.

Symbiotic fungi– Close relationship between two different

species that benefits at least one of them– Mutualistic: both benefit

Lichen

lichen: mutualistic pairing of a fungus and an alga– Photosynthetic algae feed

the fungus– Fungal mycelium provides a

good habitat

Usually a sac fungus and either green algae or cyanobacteriaMore than 25,000 “species” of lichen

Benefits of lichen symbiosis

Environments where neither could live on its own

Pioneer organisms

Tundra

Do not tolerate air pollution; death of lichen = poor air quality

Mycorrhizae

Symbiotic relationship between fungal hyphae and plant roots

Fungus provides

more water and nutrients, plant provides sugar

Mushrooms

around trees

Disease-causing fungi

30% of fungi are parasitic

Dutch Elm disease– Eliminated most elm

trees in N Amer

50 species parasitic in humans and other animals– Yeast infections

– Ringworm• Athlete’s Foot

Commercial Uses Truffles

Cheese– Fungi “ripen” them

Yeast for baking and brewing

Antibiotics

Chemical Cycling

Decompose matter

Circulate carbon and nitrogen

Some can decompose clothing, boots, glue, and plastic