Chapter 21: Kingdom Fungi Leaving Certificate Biology Higher Level

Fungi 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 Fungi Edible: –St. George’s mushroom (Calocybe gambosa) –Horse mushroom (Agaricus arvensis)

Edible v Poisonous Fungi Poisonous: –The Death Cap (Amanita phalloides) –The Destroying Angel (Amanita virosa)

Rhizopus – 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 of Rhizopus

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

Yeast 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 Reproduction

Economic Importance of Fungi Beneficial fungi: 1)Yeast is used in brewing beer 2)Edible mushrooms (St. George’s mushrooms and Horse mushrooms) Harmful fungi: 1)Rhizopus (bread mould) spoils bread and other food 2)Athlete’s foot – fungal infection of the skin between the toes 3)Potato blight – can destroy an entire potato field

Culturing 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 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