Unit 3

Kingdom Fungi

Leaving Certificate Biology

H. Jones, St. Columba’s College

Introduction• Mycology is the study of fungi.

• The general characteristics of fungi are:

• Their bodies are long thread like tubes of cells called hyphae.

• They are unicellular or multi-cellular.

• They have cell walls made from chitin.

• They have enclosed nuclei and mitochondrion.

• They reproduce by spores

• They are heterotrophic only and do not contain chlorophyll.

• Fungi include mushrooms, moulds, mildews and yeasts.

Fungal Nutrition

• Fungi can be either saprophytic (dead material), parasitic (living material causing harm) or mutualistic (symbiotic) (living material not causing harm, e.g. lichens and mycorrhiza)

• While some mushrooms are edible, some are highly poisonous and should not be consumed if not known.

• Edible mushrooms include button mushrooms, morels, field mushrooms and truffles.

Symbiotic Fungi

Parasitic Fungi

Saprophytic Fungi

Harmful and Beneficial Fungi

Beneficial Harmful

Yeast for brewing

Mushrooms are used a food

Fizzy drinks

Bread making

Cheese

Antibiotics

Human diseases (athletes foot,

dandruff, ringworm)

Plant disease (blight)

Food spoilage (Moulds and

Mildews)

Material destruction (wood)

Rhizopus stolonifer (Bread Mould)

Rhizopus is known as the

common bread mould

and is seen if bread is

left out for a long

period.

Rhizopus 1

• Nutrition

• It feeds on starchy foods, fruit, vegetable

peelings etc and is a saprophyte.

• The fungus secretes enzymes onto the

starchy substrate and the starch is broken

down outside the fungus and the nutrients

are then absorbed.

Rhizopus 2

• Structure

• The fungus appears as dark blue circular patches.

• It is often called a pin mould because it often looks

like pins sticking out of the substrate surface.

• Rhizopus composed of thread like structures called

hyphae.

• They have no crossed walls (aseptate), and are

haploid.

• A large group of hyphae is called a mycelium.

Rhizopus 3

• There are two types of hyphae, stolons and

rhizoids

• Stolons are used to spread the fungus

throughout the substrate (food)

• Rhizoids increase surface area for absorption

of the digested nutrients.

• The pin-shaped structures are used during

reproduction.

Rhizopus Life Cycle

• Rhizopus reproduces both sexually and

asexually.

Asexual Reproduction

• After a few days some hyphae grow upwards

out of the substrate.

• These are called sporangiophores.

• These structure have swollen tips contain a

sporangium, which contains many spores.

Rhizopus Life Cycle - 2

• The base of the sporangium is called a

columella.

• In dry conditions, the spores are dispersed

and are carried on the wind.

• If they land on a suitable substrate, they will

each produce a hypha and continue to grow.

• The offspring will be genetically identical to

the parent.

Rhizopus Life Cycle - 3

Sexual Reproduction

• Rhizopus exists as two strains (minus and plus).

• During sexual reproduction, hyphae of each of the

strains come close together.

• The hyphae grow towards each other and make

contact at the tip.

• The tips swell with cytoplasm and nuclei (haploid)

on both sides.

• The swelling is known as a progametangium.

Rhizopus Life Cycle - 4

• A wall forms around the progametangium,

producing an enclosed gametangium on each hypha.

• The two gametangia fuse and the many haploid

nuclei in each fuse forming diploid zygotes.

• The cell with the diploid nuclei thickens and

become a dormant zygospore.

• The zygospore remains dormant for anything up to

a number of years, and until conditions are

favourable

Rhizopus Life Cycle - 5

• Meiosis occurs inside the zygospore, producing

numerous haploid cells yet again.

• When the zygospore opens, new hyphae grow out.

• These produce sporangiophores and reproduce

asexually.

• The offspring are not genetically identical from the

parent.

Exercise

• Using you text book and other resources

write notes on Yeast (Saccharomyces)

under the following headings:

1. Structure (including diagram)

2. Reproduction

Mandatory Investigation

Yeast Structure

Reproduction in Yeast