Chapter 21: Kingdom FungiChapter 21: Kingdom FungiLeaving Certificate BiologyLeaving Certificate Biology

Higher LevelHigher Level

FungiFungi

• Fungi are eukaryotic organisms meaning that they have membrane-bound nuclei and organelles

• Types of fungi:– Saprophytic: fungi that feed on dead organic

matter, e.g. mushrooms and moulds• Some mushrooms are edible but many are

poisonous (method for identification of mushrooms involves using an expert mycologist or a mushroom key)

– Parasitic: fungi that feed on living organic matter

Edible v Poisonous FungiEdible v Poisonous Fungi

• Edible:– St. George’s mushroom

(Calocybe gambosa)– Horse mushroom

(Agaricus arvensis)

Edible v Poisonous FungiEdible v Poisonous Fungi

• Poisonous:– The Death Cap

(Amanita phalloides)– The Destroying Angel

(Amanita virosa)

Rhizopus – common bread mouldRhizopus – common bread mould• Rhizopus is a saprophytic fungus that feeds on

bread and soft fruits by secreting enzymes into the starchy substrate

• Reproduction in Rhizopus is either sexual or asexual

Structure Structure of of RhizopusRhizopus

Asexual Reproduction in RhizopusAsexual Reproduction in Rhizopus• Hyphae grow and form sporangiophores with a

sporangium on the end of each one• Each sporangium contains

many cells that develop a

tough wall – they are

now called spores• Spores are eventually

released and germinates

to produce a new

mycelium

Sexual Reproduction in RhizopusSexual Reproduction in Rhizopus• Two hyphae (plus and minus strains) grow close together• Swellings called pro-gametangia form opposite each other

eventually coming together• Nuclei enter the swelling followed by formation of a cross

wall separating the swelling from the hypha – swellings now called gametangia

• The two gametangia that are in contact with each other fuse and fertilisations occur in the gametangia to form zygospore

• Zygospore can remain dormant for a long time before germinating under favourable conditions

Yeast (Yeast (SaccharomycesSaccharomyces))• Structure:

– Yeast are single-celled fungi with a cell wall (made of chitin), nucleus, vacuoles, and a very granular cytoplasm

Yeast ReproductionYeast Reproduction

• Yeast cell reproduce asexually by a process called ‘budding’

• The yeast cell reproduces itself by mitosis and the new nucleus enters a small bud, which either remains attached to the parent cell or detaches completely

• If bud remains attached a colony can be formed by continuous budding of the new buds – however, they eventually detach to form single yeast cells

Yeast ReproductionYeast Reproduction

Economic Importance of FungiEconomic Importance of Fungi• Beneficial fungi:

1) Yeast is used in brewing beer2) Edible mushrooms (St. George’s

mushrooms and Horse mushrooms)

• Harmful fungi:1) Rhizopus (bread mould) spoils bread and

other food2) Athlete’s foot – fungal infection of the skin

between the toes3) Potato blight – can destroy an entire potato

field

Culturing MicroorganismsCulturing Microorganisms• Care should always be taken when dealing with

microorganisms – even harmless microorganisms

• Before growing microorganisms in agar everything must be sterile or otherwise be sterilised

• Asepsis is a procedure that involves avoiding all possible sources of contamination (more commonly called ‘aspetic technique’)

• Sterility involves everything be free from microorganisms

Culturing MicroorganismsCulturing Microorganisms• Before culturing microorganisms the following

should be carried out:– Hands should be washed and surgical gloves should be

worn as well as a clean lab coat– The bench/work surface should be sterilised by washing

with disinfectant such as Milton– Keep hands away from mouth and face during lab

procedures– Keep all sterile containers closed until ready to use –

such as the petri dishes (which are sterile)– Ensure the prepared agar is sterile prior to pouring into

dishes by boiling for a few minutes– Flame inoculating loops in Bunsen prior to inoculation of

dishes and after inoculation– Open all dishes for the shortest possible time to avoid

air-borne microorganisms