Chapter 31Chapter 31FUNGI FUNGI (Part 1)(Part 1)

Introduction, Ecological Impacts and PhIntroduction, Ecological Impacts and Phylogenetic Relationshipsylogenetic Relationships

Wesley Jensen, Andrew Kam, Frank Zhang, Jeff ZhangWesley Jensen, Andrew Kam, Frank Zhang, Jeff Zhang

IntroductionIntroduction Fungi are mostly eukaryotic, and multicellulFungi are mostly eukaryotic, and multicellul

ar. ar. Fungi are unique organisms that differ from Fungi are unique organisms that differ from

other eukaryotes in nutritional mode, structother eukaryotes in nutritional mode, structural organization, growth, and reproduction.ural organization, growth, and reproduction.

Fungi and Animals rose from the same ancFungi and Animals rose from the same ancestor.estor.

Absorptive NutritionAbsorptive Nutrition Fungi acquire their nutrients by Fungi acquire their nutrients by

absorptive nutrition. absorptive nutrition. Small organic molecules are absorbed Small organic molecules are absorbed

from surrounding medium.from surrounding medium. Fungi digest food outside its body by Fungi digest food outside its body by

secreting powerful hydrolytic enzymes secreting powerful hydrolytic enzymes into the food.into the food.

Absorptive Nutrition Absorptive Nutrition cont.cont.

The absorptive mode of nutrition specializeThe absorptive mode of nutrition specializes fungi into three types:s fungi into three types: Saprobic (decomposers): absorb nutrients froSaprobic (decomposers): absorb nutrients fro

m nonliving organisms.m nonliving organisms. Parasitic: Absorb nutrients from cells of living Parasitic: Absorb nutrients from cells of living

hosts. Some are pathogenic.hosts. Some are pathogenic. Mutualistic: Absorb nutrients from host, yet reMutualistic: Absorb nutrients from host, yet re

ciprocate with functions that aid partners.ciprocate with functions that aid partners. (aid with uptake of minerals from soil)(aid with uptake of minerals from soil)

Fungi GrowthFungi Growth Bodies of fungi are constructed of units calBodies of fungi are constructed of units cal

led hyphae.led hyphae. Hyphae: minute threads composed of tubular Hyphae: minute threads composed of tubular

walls surrounding plasma membranes and cytwalls surrounding plasma membranes and cytoplasm.oplasm.

Hyphae form a network called mycelium, which Hyphae form a network called mycelium, which is the “feeding” network of the fungus.is the “feeding” network of the fungus.

Fungi Growth cont.Fungi Growth cont. Most fungi are multi-cellular with hyphae diMost fungi are multi-cellular with hyphae di

vided into cells by cross-walls (septa).vided into cells by cross-walls (septa). The The septasepta have pores large enough to allow rib have pores large enough to allow rib

osomes, mitochondria, and nuclei to flow from osomes, mitochondria, and nuclei to flow from cell to cell.cell to cell.

The hyphae are built from The hyphae are built from chitinchitin (polypeptid (polypeptide similar to chitin found in external skeletoe similar to chitin found in external skeletons of insects)ns of insects)

Fungi Growth cont.Fungi Growth cont. Some fungi are Some fungi are aseptateaseptate, meaning their hy, meaning their hy

phae are not divided into walls. phae are not divided into walls. They are known asThey are known as coenocytic coenocytic fungi. fungi.

Instead, they consist of a continuous cytoplasInstead, they consist of a continuous cytoplasmic mass with hundreds or thousands of nuclemic mass with hundreds or thousands of nuclei.i.

Fungi usually have modified hyphae called Fungi usually have modified hyphae called hhaustoriaaustoria which penetrate tissues of a hos which penetrate tissues of a host cell.t cell.

Fungal Reproduction Fungal Reproduction (Asexual)(Asexual)

They reproduce by releasing spores which They reproduce by releasing spores which are produced from specialized hyphal strucare produced from specialized hyphal structures.tures. Spores are created asexually, and are carried Spores are created asexually, and are carried

by wind or water.by wind or water. They germinate if they are in a moist area.They germinate if they are in a moist area.

Fungal Reproduction Fungal Reproduction (Sexual)(Sexual)

Sex is a contingency mode of Sex is a contingency mode of reproduction that occurs when there reproduction that occurs when there has been a change in the has been a change in the environment.environment.

Sexual reproduction results in Sexual reproduction results in greater genetic diversity among greater genetic diversity among offspring.offspring.

Fungal Sex CycleFungal Sex Cycle Syngamy is the sexual union of cells that fSyngamy is the sexual union of cells that f

orm two individuals. orm two individuals. There are two stages:There are two stages:

Plasmogamy: Fusion of CytoplasmPlasmogamy: Fusion of Cytoplasm Karyogamy: Fusion of nuclei.Karyogamy: Fusion of nuclei.

PlasmogamyPlasmogamy In plasmogamy, the nuclei from each parenIn plasmogamy, the nuclei from each paren

t cell pair up but do not fuse, this forms a t cell pair up but do not fuse, this forms a dikaryon (two nuclei)dikaryon (two nuclei)

Instead they coexist, providing advantages Instead they coexist, providing advantages in the cell’s life.in the cell’s life. One haploid genome compensates for harmful One haploid genome compensates for harmful

mutations in the other nucleus.mutations in the other nucleus.

KaryogamyKaryogamy In karyogamy, the nuclei fuse, forming a diIn karyogamy, the nuclei fuse, forming a di

ploid cell that undergoes immediate meiosiploid cell that undergoes immediate meiosis.s.

Ecosystems Depend on Ecosystems Depend on Fungi as Decomposers and Fungi as Decomposers and

SymbiontsSymbionts Breakdown of wood, which makes Breakdown of wood, which makes

nutrients available to living organism, nutrients available to living organism, became a dominant group of became a dominant group of organisms about 250 million years organisms about 250 million years agoago

Without fungi and bacteria, plants and Without fungi and bacteria, plants and animals would starve because animals would starve because elements taken from soil wouldn’t be elements taken from soil wouldn’t be returnedreturned

ContinuedContinued Fungi’s invasive hyphae enter the tissues and Fungi’s invasive hyphae enter the tissues and

cells of dead organic matter and hydrolyze cells of dead organic matter and hydrolyze polymers. polymers.

Fungi can decompose anything from Fungi can decompose anything from fruits/dung/forest litter to shower curtains and fruits/dung/forest litter to shower curtains and wooden boats.wooden boats.

We lose 10% to 50% of the world’s fruit harvest We lose 10% to 50% of the world’s fruit harvest due to fungal attack.due to fungal attack.

Ethylene, a plant hormone that causes fruit to Ethylene, a plant hormone that causes fruit to ripen also stimulates fungal spores on the fruit ripen also stimulates fungal spores on the fruit surface to germinate, causing the invasion of surface to germinate, causing the invasion of the fungi.the fungi.

Some Fungi are Some Fungi are PathogensPathogens

Plant diseases caused by fungi:Plant diseases caused by fungi: Ascomycete that causes Dutch elm disease has Ascomycete that causes Dutch elm disease has

drastically changed the landscape of NE United drastically changed the landscape of NE United StatesStates

Aspergillus which is a species of mold which could Aspergillus which is a species of mold which could contaminate improperly stored grain secretes contaminate improperly stored grain secretes aflatoxins which is a carcinogenicaflatoxins which is a carcinogenic

Ergots, caused by one type of ascomycete, that Ergots, caused by one type of ascomycete, that are ground with rye could cause humans to have are ground with rye could cause humans to have hallucinations, temporary insanity, nervous hallucinations, temporary insanity, nervous spasms, gangrene spasms, gangrene

Phylogenetic Phylogenetic Relationships of FungiRelationships of Fungi

Fungal ancestors were aquatic flagellated Fungal ancestors were aquatic flagellated organisms.organisms.

Flagellated cells were lost as they became Flagellated cells were lost as they became adapted for life on land.adapted for life on land.

The differences between the Zygomycota, The differences between the Zygomycota, Ascomycota, and Basidiomycota are focused Ascomycota, and Basidiomycota are focused on their solutions to reproducing and on their solutions to reproducing and dispersing on land.dispersing on land.

Comparisons of RNA show that fungi are more Comparisons of RNA show that fungi are more closely related to animals than to plants.closely related to animals than to plants.

Many Animals, including Many Animals, including humans, eat fungihumans, eat fungi

A variety of mushrooms are A variety of mushrooms are consumed in various cultures.consumed in various cultures.

Only an expert can determine safe to Only an expert can determine safe to consume mushrooms.consume mushrooms. There is no simple rule to determine There is no simple rule to determine

poisonous and nonpoisonous. poisonous and nonpoisonous. Truffles are the most commonly Truffles are the most commonly

consumed mushroom.consumed mushroom.