Fungi

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Interesting facts about fungi

There are more than 60 species of fungi that exhibit the phenomenon of emitting light from their bodies known as bioluminescence.

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People eat mushrooms of all shapes, sizes and colors. Yeasts are used in making bread, wine, beer and solvents.

Drugs made from fungi cure diseases and stop the rejection of transplanted hearts and other organs. Fungi are also grown in large vats to produce flavourings for cooking, vitamins and enzymes for removing stains.

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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.

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Features of Fungi

• Heterotrophic (Do not make their own food)

• No chlorophyll• Mostly multi-cellular• Made up of threads called

hyphae• Hyphae combine in masses to

form a mycelium• Their walls are made of a

carbohydrate called chitin (found in insect bodies)

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Features

• They reproduce by means of spores.

• They do not ingest food but instead they secrete enzymes onto their food and then absorb the nutrients through their rhizoids.

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Nutrition

All fungi are heterotrophs i.e. they take in food made

by other organisms.

Edible fungi e.g. field mushrooms, truffles

Poisonous fungi e.g. death cap

Fungi are either:• Parasitic• Saprophytic

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Nutrition

1. ParasitesLive off a live host and cause harm.e.g. athletes foot or ringworm.Obligate parasites canonly live off a host and not ontheir own. e.g. smuts and rusts.

2. SaphrophytesMost fungi are saphrophytes and these live off deadmaterial. e.g. ear fungus on dead wood. They are essential

for recycling nutrients.

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Parasitic Fungi• Obligate parasites

– live on live hosts but do not normally kill them

• Facultative parasites – kill the host and feed

on the remains

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• 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

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Rhizopus

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Bread Mould (Rhizopus)

This fungus grows on the starch in bread,

vegetable peelings and stored fruits.

Digestion takes place outside of the fungus

and the nutrients are absorbed.

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RhizopusStructure

• The mould is often called pin mould as it's reproductive

• structures look like pins.• Tubes called hyphae form a big mass called a

mycelium.• The hyphae digest and absorb the starch in the

bread.• A stolon is an aerial hyphae (stands up) which

allows the mould to spread more quickly.

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Rhizopus growing on agarC. Shevlin

Structure of Rhizopus

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Rhizopus to Label

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Functions of parts of Rhizopus

Part Function

Hyphae Spread the fungus & absorb nutrients

Mycelium Spread the fungus

Sporangium Produces the spores

Sporangiophore Holds up the sporangium

Stolon Allows fungi to spread

Columella Spore releaseC. Shevlin

Structure of Rhizopus

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Facts about bread mould:

1. Bread mould consists of threadlike structures called Hyphae

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

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3. Large numbers of hyphae are called a mycelium

4. The hyphae digest the substrate on which they grows

5. Rhizoids provide extra surface area for absorption of the digested material

6. Stolons are arial hyphae which allow Rhizopus to spread sideways

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Sporangiophore

Apophysis

Columella

Sporangium

Spores

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Rhizopus: Sporangia

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Life cycle of Rhizopus

Two types of reproduction:

1. Asexual Reproduction2. Sexual Reproduction

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Asexual reproduction in Rhizopus• Only involves one parent.• Does not involve fertilisation• Offspring are identical to parent

1. Hyphae called sporangiospores grow up into the air. Their tips swell to form sporangium.

2. Cells inside the sporangium produce haploid spores by mitosis. (Sporulation is the process of making spores).

3. In dry conditions the sporangium opens and spores are released.

4. Spores are carried by the wind and if they land on a suitable substrate they germinate.

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Spores being released from Sporangium

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Sexual Reproduction

• Involves two parents• Involves fertilisations and offspring are not

identical to parents.

Rhizopus doesn't have a male or female but we call them + or - .

Both look identical but sexual reproduction needs a plus and a minus strain to happen.

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Steps in Sexual ReproductionSteps in Sexual Reproduction

1.Hyphae from opposite strains grow close together.

2. Swellings form opposite each other.

3. The swellings touch.

4. Nuclei (gametes) move into each swelling.

5. Cross walls form and form gametangia.

6. The walls dissolve.7. Many fertilisations happen to make diploidzygote nuclei. C. Shevlin

Sexual Reproduction

8. A tough walled black zygospore forms around the nuclei.

9. Zygospore germinates by meiosis when conditions are right.

10. A haploid hyphae grows out and makes a sporangiophore with a sporangium This produce new haploid spores which can grow.

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Sexual reproduction

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

+ Strain - Strain

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Sexual reproduction

• When hyphae from opposite strains grow close together swellings grow on both strains and touch each other.

+ Strain - Strain

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Sexual reproduction

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

+ Strain - Strain

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Sexual reproduction

• Cross-walls form to produce gametangia.

+ Strain - Strain

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Sexual reproduction

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

+ Strain - Strain

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Sexual reproduction

• A zygospore forms around these nuclei.

• When conditions are suitable the zygospore germinates by meiosis.

+ Strain - Strain

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Sexual reproduction

• A zygospore forms around these nuclei.

• When conditions are suitable the zygospore germinates by meiosis.

+ Strain - Strain

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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.

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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

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• 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

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YeastThe yeast fungus consists of single

cells rather than hyphae

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Structure of yeast

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Yeast

• Another name for yeast is Saccharomyces.• They can be round or oval in shape.• They can usually only be seen with an• electron microscope.• Yeast have thin walls made of chitin.• They have a thick cytoplasm with many food

storage vacuoles.

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Respiration in YeastRespiration• Yeasts respire anaerobically (without

Oxygen) and break down glucose to produce ethanol (alcohol) and Carbon Dioxide.

• Glucose 2 Ethanol + 2 Carbon dioxide.• This process is called fermentation.• Fermentation is a type of anaerobic

respiration

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Reproduction in Yeast

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Reproduction in Yeast

Asexual Reproduction

This is done by budding.

The parent cell divides by Mitosis and the new nucleus and cytoplasm enter the new cell.

If the buds don't separate they form a colony

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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.

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Asexual reproduction in yeast

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

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• 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

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Budding

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Budding

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Economic importance of fungi

Beneficial fungi• Making bread and

alcohol e.g. wine and beer.

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

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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

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Decomposition

Certain species of fungi and bacteria are decomposers.

Over time, without decomposition, so much nitrogen would be locked up in leaves and other tissues that there would not be enough nitrogen available for the plant to make new leaves, stems and wood.

The surface of the ground would also be buried by dead leaves and wood lying forever where they fell.

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Experiment to grow leaf yeast

Sterile means that all microorganismsare destroyed. i.e. there is nothing living.For this experiment we Ash or Ivy leaves. We cut them into

circles and stick them face up to the inside of the dish lid.The yeast spores drop off the leaves onto the agar. They

start to grow and form pink colonies.Important to keep the bench sterile we wash ourhands, the desk and all equipment with disinfectant.We also put the tweezers etc. through a bunsen flame.This is Saccharomyces roseus.

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What have you learned?

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• 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

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2011 Paper > Section C > Question 15 > Part c

2011 Paper > Section C > Question 15 > Part c

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