Fungi

Learning Objectives• Define the terms: saprophytic & parasitic• State the structure & life cycle of Rhizopus• Explain nutrition in fungi.• Outline the structure & reproduction of Yeast• Name 2 Beneficial & 2 Harmful fungi• Mention that there are Edible and Poisonous

fungi• Identify and state functions for the following

structures: rhizoid, sporangium, gametangium, zygospore.

Features of Fungi• They do not make their

own food• They are mostly multi-

cellular• They are made up of

threads called hyphae• Hyphae combine in

masses to form a mycelium

• Their walls are made of a carbohydrate called chitin

Nutrition

• All fungi are heterotrophs i.e. they take in food made by other organisms

Fungi are either:• Parasitic• Saprophytic

• Most fungi are saprophytic

• obtain nutrients from dead material

• As they digest it minerals are released and recycled

• Play a vital role in the environment as they are responsible for decay

• E.g. mushrooms and moulds

Saprophytic fungi

Parasitic Fungi• Absorb their food

from live hosts• They get their food

mostly from plants although some fungal parasites live on animals e.g. athlete’s foot

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Athletes.jpg/220px-

Athletes.jpg

Parasitic Fungi• Obligate parasites

– live on live hosts but do not normally kill them

• Facultative parasites – kill the host and

feed on the remains

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Athletes.jpg/220px-

Athletes.jpg

Symbiosis• Some fungi e.g. form

symbiotic relationships with other organisms

• A lichen is an organism which is a combination of a fungus and an alga

Edible and poisonous fungi• Some fungi are

edible, but many are poisonous if eaten

• It is often difficult to distinguish between the edible and poisonous varieties growing in the wild

Learning Check

• What is a saprophytic fungi?• Give an example of a saprophytic fungi• What is a parasitic fungi?• What is an obligate parasite?• What is facultative parasite?• Give an example of a parasitic fungi

Rhizopus

Rhizopus growing on agar

Structure of Rhizopus

Hypha

Consists of threadlike structures called Hyphae

They are tubular with no cross walls and are multinucleate. Each nucleus is haploid.

Nucleus

Large numbers of hyphae are called a mycelium

• The hyphae digest the substrate on which they grows• Rhizoids provide extra surface area for absorption of

the digested material • Stolons are arial hyphae which allow Rhizopus to

spread sideways

Structure of Rhizopus

Sporangiophore

Apophysis

Columella

Sporangium

Spores

Learning Check

• Can you draw and label the structure of Rhizopus?

• What is a hypha?• What is a mycelium?• What is the function of a rhizoid?• What is a stolon?

Life cycle of Rhizopus

Asexual reproduction• Sporangiophores

grow up from the substrate after a number of days

• Cells within the sporangium divide by mitosis to produce spores (haploid)

Asexual reproduction• Cells within the

sporangium divide by mitosis to produce spores (haploid)

Asexual reproduction• The sporangium dries

out in the right conditions and opens releasing many spores.

• Each spore will grow into a new hypha and mycelium if it lands on a suitable substrate

Sexual reproduction• Sexual reproduction

in Rhizopus can only occur between a plus and a minus strain.

+ Strain - Strain

Sexual reproduction• When hyphae from

opposite strains grow close together swellings grow on both strains and touch each other.

+ Strain - Strain

Sexual reproduction• Nuclei from both

hyphae move into these swellings which are now called progametangia.

+ Strain - Strain

Sexual reproduction• Cross-walls form to

produce gametangia.

+ Strain - Strain

Sexual reproduction• The walls of the

gametangia dissolve and a number of fertilisations take place producing diploid zygote nuclei.

+ Strain - Strain

Sexual reproduction• A zygospore forms

around these nuclei.• When conditions are

suitable the zygospore germinates by meiosis.

+ Strain - Strain

Sexual reproduction• A zygospore forms

around these nuclei.• When conditions are

suitable the zygospore germinates by meiosis.

+ Strain - Strain

Sexual reproduction• A hypha grows out of

the zygospore and produces a sporangium at the tip.

• The sporangium opens releasing many haploid spores which grow into new individuals.

Review of sexual reproduction• Sexual reproduction in Rhizopus can only

occur between a plus and a minus strain• When hyphae from opposite strains grow

close together swellings grow on both strains and touch each other

• Nuclei from both hyphae move into these swellings which are now called progametangia

• Cross-walls form to produce gametangia

• The walls of the gametangia dissolve and a number of fertilisations take place producing diploid zygote nuclei

• A zygospore forms around these nuclei• When conditions are suitable the zygospore

germinates by meiosis• A hypha grows out of the zygospore and

produces a sporangium at the tip • The sporangium opens releasing many haploid

spores which grow into new individuals

Review of sexual reproduction

Learning Check

• How does Rhizopus reproduce?• What is a prometangia?• How is a gametangia formed?• How is a zygospore formed?• What is produced at the tip of a hypha?

Yeast

Structure of yeast

Reproduction in Yeast

Asexual reproduction in yeast• Asexual reproduction in yeast occurs by

budding.• The nucleus of the parent cell divides by

mitosis. One of the daughter nuclei enters a small developing bud on the outside of the yeast cell.

Asexual reproduction in yeast

• This bud can separate from the parent to become a new individual

• This bud can separate from the parent to become a new individual

• In some cases the bud does not separate, but can itself bud. In this way long colonies of yeast cells can develop

Asexual reproduction in yeast

Budding

Budding

Economic importance of fungi

Beneficial fungi• Yeasts can be used to

make bread and alcohols such as wine and beer

• Fungi can be used as a source of food e.g. mushroom

Harmful fungi• Fungi can attack crops

e.g. corn and wheat and cause major financial losses as a result

• Fungi such as athletes foot and ringworm can infect animals

• Fungi can spoil food e.g. rhizopus grows on bread

Economic importance of fungi

Learning Check

• Can you draw the structure of yeast?

• Describe how yeast reproduces

• Give an example of how yeast is important economically

Syllabus: Depth of treatment

• Saprophytic and parasitic forms• Rhizopus (Structure and life cycle)• Nutrition• Yeast: structure and reproduction

(budding).

• Mention of edible and poisonous fungi.• Economic importance of fungi:

examples of any two beneficial and any two harmful fungi.

Practical Activities

• Investigate the growth of leaf yeasts using agar plates and controls

Contemporary issues and Technology