Fungi - Leaving Cert Biology

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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
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