Fungi - BIOLOGY JUNCTION

Fungi
All Materials © Cmassengale

Characteristics

Eukaryotic
Do not contain chlorophyll
Nonphotosynthetic
Absorptive heterotrophs – digest food first & then absorb it into their bodies
Release digestive enzymes to break down organic material or their host
Store food energy as glycogen
Most are saprobes – live on other dead organisms
Important decomposers & recyclers of nutrients in the environment
Most are multicellular, but some unicellular like yeast
Some are internal or external parasites; a few are predators that capture prey
Nonmotile
Lack true roots, stems, & leaves
Cell walls are made of chitin (a complex polysaccharide)
Grow as microscopic tubes or filaments called hyphae that contain cytoplasm & nuclei
Hyphal networks are called mycelium
Some are edible
Reproduce by sexual & asexual spores
Antibiotic penicillin comes from Penicillium mold
Classified by their sexual reproductive structures
Grow best in warm, moist environments preferring shade
Mycology – study of fungi
Fungicide – chemicals used to kill fungi
Includes yeasts, molds, mushrooms, ringworm, puffballs, rusts, smuts, etc.
Fungi may have evolved from prokaryotes by endosymbiosis

Vegetative (nonreproductive) Structures of Fungi

HYPHAE

Each hyphae is one continuous cell
Hyphae continually grow & branch
Septum (septa-plural) are cross walls with pores to allow the movement of cytoplasm in hyphae
Hyphae with septa are called septate hyphae
Hyphae without septa are called coenocytic hyphae

Tangled mats of hyphae are known as mycelium
All hyphae within a mycelium share the same cytoplasm so materials move quickly
Hyphae grow rapidly from the tips by cell division
Stolon is a horizontal hyphae that connects groups of hyphae to each other
Rhizoids are rootlike parts of hyphae that anchor the fungus

Reproductive Structures

Most fungi reproduce asexually & sexually
Asexual reproduction produces genetically identical organisms & is the most common method used
Sexual reproduction in fungi occurs when nutrients or water are scarce
Fruiting bodies are modified hyphae that make asexual spores
Fruiting bodies consist of an upright stalk or sporangiophore with a sac containing spores called the sporangium

SPORANGIOPHORES

Types of fruiting bodies include basidia, sporangia, & ascus
Spores – haploid cells with dehydrated cytoplasm & a protective coat capable of developing into new individuals
Wind, animals, water, & insects spread spores
When spore lands on moist surface, new hyphae form

Asexual Reproduction in Fungi

Fungi reproduce asexually when environmental conditions are favorable
Some unicellular fungi reproduce by mitosis
Yeast cells reproduce by budding where a part of the cell pinches off to produce more yeast cells

Athlete’s foot fungus reproduce by fragmentation from a small piece of mycelium
Most fungi reproduce asexually by spores
Penicillium mold produces spores called conidia without a protective sac on the top of a stalk called the conidiophore

Sexual Reproduction in Fungi

Fungi reproduce sexually when environmental conditions are unfavorable
No male or female fungi
Two mating types — plus (+) and minus (-)
Fertilization occurs when (+) hyphae fuse with (-) hyphae to form a 2N or diploid zygote
Some fungi show dimorphism (ability to change their form in response to their environmental conditions)

Classification of Fungi

Fungi are classified by their reproductive structures
The 4 phyla of fungi are Basidiomycota, Zygomycota, Ascomycota, & Deuteromycota

Zygomycota

No septa in hyphae (coenocytic)
Asexual reproductive structure called sporangium & produces sporangiospores
Rhizoids anchor the mold, release digestive enzymes, & absorb food
Asexual reproductive structure called sporangium & produces sporangiospores
Sexual spore produced by conjugation when (+) hyphae & (-) fuse is called zygospore
Zygospores can endure harsh environments until conditions improve & new sporangium

Basidiomycota

Called club fungi
Includes mushrooms, toadstools, puffballs, bracket fungi, shelf fungi, stinkhorns, rusts, & smuts
Some are used as food (mushroom) & others cause crop damage (rusts & smuts)
Seldom reproduce asexually
Basdiocarp made up of stalk called the stipe & a flattened cap
Stipe may have a skirt like ring below cap called the annulus
Gills are found on the underside of the cap & are lined with basidia
Basidium – sexual reproductive structure that make basidiospores
Basidiospores are released from the gills & germinate to form new hyphae & mycelia
Vegetative structures found below ground & include rhizoids (anchor & absorb nutrients), hyphae, & mycelia

Ascomycota

Some are parasites causing Dutch elm disease & chestnut blight
Sac Fungi can reproduce both sexually and asexually
Yeast reproduce asexually by budding (form small, bud-like cells that break off & make more yeasts)
Asexual spores called conidia form on the tips of specialized hyphae called condiophores
Ascocarp – specialized hyphae formed by parent fungi during sexual reproduction
Ascus – sacs within the ascocarp that form spores called ascospores

Lichens

Symbiotic association between a sac fungus & a photosynthetic green algae or cyanobacteria
Both organisms benefit (algae makes food & fungus supplies moisture, shelter, & anchorage)
Grow on rocks, trees, buildings, etc. & help form soil
Crustose lichens grow on rocks & trees; fructose lichens grow shrub-like; foliose lichens grow mat-like on the soil

Mycorrhizae

Importance of Fungi