Chapter 22 Fungi

, Mycology – is the study of fungi Characteristics of Fungi:  Fungi are eukaryotic – have membrane enclosed organelles.  Fungi are heterotrophic – take in food made by other organisms and lack chlorophyll.  They have cell walls made of chitin.  Body structure – consists of tubes called hyphae – form a visible mycelium.  Reproduce asexually and sexually.

Nutrition in Fungi (Two types of fungi) Parasites - Absorb food from live hosts Saprophytes Absorb food from dead organic matter

Parasitic Fungi:  Mostly feed off plants – e.g. potato blight fungus.  Some live on animals – athlete’s foot, ringworm.athlete’s foot  Obligate Parasites live on live hosts – do not kill host e.g. mildews, smuts.  Facultative parasites – may kill host e.g. fungi causing soft rot in fruit.

Saprophytic Fungi:  Feed off dead plants and animals and cause decay – e.g. mushrooms and mould.  in the environment.

Edible and Poisonous Fungi Edible  Field Mushrooms  Morels  Truffle Poisonous  Death Cap  Destroying Angels  CordycepsCordyceps

Two types of fungi to be studied Rhizopus (Bread Mould) Saccharomyces (Yeast)

Rhizopus

Rhizopus (Bread Mould) Nutrition in rhizopus  Bread Mould is saprophytic.  It feeds of bread and fruits.  It secretes enzymes which digests the food.  It has rhizoids and hypha that absorb the digested food.

Structure of Rhizopus

Rhizopus consists of threadlike structures called hyphae and it is a multicellular fungus. Hyphae: digest and absorb the substrate on which they grow. Mycelium: is a mass of hyphae.

Stolon: is a hypha which grows over the surface of the food to allow the fungus to spread more rapidly. Rhizoids: create a larger surface area for the absorption of food. Sporangiophore: supports the sporangium and allows the spores to be more easily dispersed.

Life Cycle of Rhizopus Asexual Reproduction:  Hyphae grow upwards to form sporangiophores the tip of which swells to produce the sporangium.  Sporangium divides by mitosis to produce cells.  Each cell develops a wall and is now called a spore.

 The sporangium cracks in the wind.  Spores are dispersed.  If they fall on suitable substrate they grow into new hypha and mycelium.

RHIZOPUS– Asexual Reproduction

Sexual Reproduction Rhizopus exists as two separate strains called plus and minus strains. + Strain- Strain Sexual reproduction in Rhizopus can only occur between a plus and a minus strain.

+ Strain- 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. + Strain- Strain

+ Strain- Strain Cross-walls form to produce gametangia.

+ Strain- Strain 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. + Strain- Strain

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.

Saccharomyces (Yeast) Structure of Yeast  It is a unicellular fungus.  Yeast cells are round or oval.  Yeast cells have thin walls made of chitin.  Yeast cells have a thick granular cytoplasm.

 Usually one large vacuole present.  Each cell has one nucleus.  Yeasts respire anaerobically: Glucose → 2 ethanol + 2 carbon dioxide.

Reproduction in Yeast Reproduction in yeast is asexual by a process called budding. Budding: 1) A small bud forms at the side of the cell. 2)The nucleus divides by mitosis. 3)One of the new nuclei enters the bud.

4) The bud fills with cytoplasm 5) a) The bud can remain attached and form a colony. b) OR the bud can break free and form its own colony. N.B.: Please know and be familiar with the diagrams illustrating the process of budding

Asexual Reproduction in Yeast

Economic Importance of Fungi ( Must know two benefits and two disadvantages) Benefits 1)Yeast – used to produce alcohol. 2)Penicillium – used to produce antibiotic penicillin. 3)Puffball Mushroom – is a food (edible). Disadvantages 1)They destroy food, crops and a wide range of other materials: - Rhizopus stolonifer – causes bread mould. 2)Fungal diseases of plants, humans and animals can result in financial losses.humans 3)Death Cap Mushroom – poisonous if eaten.