CHAPTER 31: FUNGI

How do Fungi acquire nutients?

They are Heterotrophs that get nutrition from absorption

-- secretes hydrolytic enzymes into food then absorbs

-- therefore they are decomposers, parasites, or mutualistic symbionts (Lichens – fungi and algae living together)

Because of this mode of nutrition, fungi have evolved what structure to provide for both extensive surface area and rapid growth?

Mycelium – interwoven mats made of hyphae

Hyphae – small threads made of tubular cell walls (made of chitin)surround the plasma membrane. They are divided into cells by cross walls called septa.

http://biodidac.bio.uottawa.ca/ftp/BIODIDAC/FUNGII/BASIDOMY/DIAGBW/BASI007B.GIF

Images from your book. Figures 31.2 and 31.3

How do cell walls of fungi differ from the cell walls of plants?Plants cell walls are made of celluloseFungi cell walls are made of chitin

What are the septa comparable to in plant cells (even though septa are bigger)?

Plasmodesmata

Define these terms:Mycelium – Densely branched network of hyphae in a fungus

Septa – A cross wall that divides a fungal hypha into cells. Pores are large enough to allow ribosomes, mitochondria, and nuclei to flow from cell to cell.

Coenocytic fungi – a fungus that lacks septa. It’s body is made up of a conitnuous cytoplasmic mass that may contain hundreds or thousands of nuclei.

Haustoria – modified hyphae on parasitic fungi enabling it to penetrate the cell walls of plants (however, it remains enclosed in the plasma membrane of the plant).

Mycorrhizae – mutualistic relationship between plant roots and fungi-- Plant provides fungus with a steady supply of sugar-- Fungus increases the suface area for water uptake and also supplies plant with phosphate and other minerals absrobed from the soil. Fungus also secretes growth factors that stimulate roots to grow and branch and antibiotics that help protect the plant from disease.

Ectomycorrhizal Fungi – Forms a dense sheath over the surface of the root

Arbuscular mycorrhizal fungi – (aka Endomycorrhizae) – microscopic fungal hyphae extend into the root. Makes extensive contact with the plant through brancing of hyphae that forms arbuscules.

Reproduction

Fungal spores

a. reproduced sexually or asexually (Sexual reproduction only occurs when there has been some change in environment)

b. unicellular or multicellular

c. produced in specialized hyphal structures

d. carried by wind or water

a. contributes to adaptation in changing environment

Heterokaryotic Stage “different nuclei” Dikaryon (n+n)“two nuclei”, one cell

Diploid Stage (2n)

Spore producing structures (n)

Spores

Mycelium (n)

KaryogamyHaploid nuclei fuse producing a diploid cell

Meiosis immediately

Germination

PlasmogamyUnion of 2 parent mycelia

(n)

Mycelium (n)

Spore Producing Structures (n)

Spores (n)

Germination

How do fungi contribute to an ecosystem?DecomposersSome produce antibioticsFoodYeast (alcohol, bread)Cholesterol lowering drugsHigh blood pressure medicineMolecular genetics research (easy to culture and manipulate)

What are some examples of how fungi are important to humans?

Diversity of Fungi (4 divisions)

1. Chytridiomycota

a. may be link between fungi and other Eukaryotics

b. mainly aquatic

c. decomposers or parasitic

d. make uniflagellated spores called zoospores

e. coenocytic hyphae

f. most primitive

2. Zygomycota – “zygote fungi”

a. mostly terrestrial

b. live in soil or on dead plants and animals

c. major group forms mycorrhizae

d. coenocytic – septa only found where reproductive cells are formed.

e. common one is black bread mold 3. Glomeromycetes (formerly thought to

be Zygomycetes)

a. Many plants form mycorrhizal associations with this fungi

4. Ascomycota – “sac fungi”

a. all habitats

b. lichens, mycorrhizae, live on leaves and release toxins to protect plant from insects

c. defining feature – production of sexual spores in saclike asci

This is the sexual stage – dikaryon – seen in macroscopic fruiting bodies called ascocarps

Dikaryon hypae give rise to asci

Karyogamy takes place withing asci

Meiosis produces ascospores (8 in a row) ****Think meiosis lab!!!!!!

5. Basidiomycota – “Club Fungi”

a. mushrooms, puff balls

b. decomposers, mycorrhizae, parasites

c. long lived dikaryotic mycelium

d. reproduces sexually

6. Lichens

a. Symbiotic association of millions of photosynthetic microorganisms held in a mesh of fungal hyphae.

Algae provides fungus with food

Fungus gives algae a suitable environment for growth