Fungi

What are examples of fungi?

Diversity and Importance of Fungi

Fungi come in a variety of shapes and sizes.

For example, Ontario forests have a variety of

natural growing mushrooms. The part of the

mushroom above ground is just a small portion of

the entire organism.

The “fairy ring” mushroom may be 100 m in diameter

with some documented cases of more than 5.5 km.

Diversity and Importance of Fungi

Fungi can often be mistaken for plants, given that

they can be seen growing off logs or wet leaves on

the ground.

However, evolutionarily speaking, fungi are more

closely related to animals then they are to plants.

Characteristics of Fungi

Unlike plants, fungi cannot photosynthesize to make

their own food.

They are heterotrophic organisms that breakdown

organic matter in the environment into nutrients

using digestive enzymes.

These nutrients can then be absorbed by the fungi.

Fungi also take in oxygen from the environment for

cellular respiration.

Mushrooms, moulds, mildew, yeast, truffles, and rusts

are common representatives of the fungi kingdom.

Ecological Roles

Many fungi play an important ecological role as decomposers.

Fungi recycle nutrients such as nitrogen and carbon by breaking down organic material.

Common food sources of fungi include fallen logs, bodies of dead animals, or wastes of living organisms.

Fungi often live in a symbiotic relationship with plants in which they exchange nutrients

Fungi can also be parasites, absorbing nutrients from the cells or body fluids of living hosts.

Parasitic fungi can cause a variety of plant diseases including wheat rust, corn smut, rot, and blight

Parasitic fungi can also cause diseases in humans, such as ringworm and athlete’s foot.

Structure and Function

Yeast is an example of a unicellular fungus, though

most fungi are multicellular.

The general structure of most multicellular fungi

includes several structures: hyphae, mycelium, and

fruiting bodies.

Hyphae

Hyphae are threads of cytoplasm surrounded by a

plasma membrane and covered by a cell wall

composed of chitin.

Hyphae usually have cell walls called cross-walls or

septum which divide the long filaments into many

separate cells. However large pores allow

cytoplasm and organelles to flow from cell to cell.

This movement helps to redistribute nutrients from one

part of its body to another.

Mycelium

The branching of the hyphae forms an interwoven

mat known as the mycelium (plural is mycelia).

The mycelium forms a large underground mass,

forming the majority of the organism.

It functions as the feeding structure of the fungi. Its

fibrous structure increases surface area for

absorption of nutrients.

Fungi are not mobile but the mycelium can grow

and branch out to expand their network.

Mycorrhizae

The large underground networks of mycelia can

form mycorrhizae, which are fungi that form

mutualistic association with plant roots.

The fungus receives sugars, starches, proteins, and

lipids from the plant roots. In return, the fungus acts

as an extension of the plant roots and collects

nutrients and water for the plant.

Since hyphae are tiny in diameter, they can

penetrate places that plant roots cannot.

Fruiting Body

In larger mushrooms, the part that appears above

ground is known as the fruiting body.

This is the reproductive structure of the mushroom.

Reproduction

Fungi can reproduce both sexually and asexually.

Asexual reproduction

A fungi releases spores which can be dispersed by the

wind or other factors.

Spores are haploid cells with thick cell walls that can

withstand unfavourable conditions.

When conditions are favorable, the spores can

germinate to form mycelium.

Reproduction

Sexual reproduction

The two sexes of fungi are assigned the symbols “+” or

“-”.

The haploid hyphae of opposite sexes will grow

towards each other a fuse to form a diploid

zygospore.

The zygospore generates haploid spores that are

genetically unique, increasing genetic diversity.

Reproduction

Sexual reproduction in fungi with fruiting bodies

When the haploid hyphae fuse, they produce a

dikaryotic hyphae.

The dikaryotic hyphae has two nuclei per cell.

This grows into the fruiting body above ground.

When the nuclei eventually fuse to form a diploid

nucleus, the cell can then divide into haploid spores to

begin the cycle again.

Major Phyla of Fungi

Phylum Reproductive Structure Examples

Zygomycota

(common moulds)

Zygospores that contain sexual

spores which are resistant to

unfavorable conditions

Black bread mould,

‘hat thrower’

Basidiomycota

(club fungi)

Club-shaped cell that contains

sexual spores

Mushrooms, club fungi,

shelf fungi, puffballs,

rusts

Ascomycota

(sac fungi)

Asci sacs that contain sexual

sporesYeast, truffles, morels

Chytridomycota

(chytrids)

Only fungi type with flagellated

sporesChytrids