Fungi
Fungi are heterotrophic organisms that can be single-celled or multicellular. They do not contain chlorophyll.
All fungi are eukaryotic – meaning they have a membrane-bound nucleus and membrane-bound organelles.
All fungi have cell walls made of chitin.
Nutrition: way in which organisms obtains and uses food.
All fungi are heterotrophic – of which there are two types: saprophytic and parasitic.
Saprophytic fungi: obtain their food from dead organic matter; e.g. fungi of decay.
Parasitic fungi: obtain their food from living organisms; e.g. Athlete’s foot
Yeast (Saccharomyces cerevisiae)
Structure
Single-celled
Cell wall made of chitin
Granular cytoplasm
Reproduction
Asexual by mitosis in a process known as ‘budding’.
Rhizopus (Common bread mould)
Structure
Multicellular
Cell wall made of chitin
Hyphae – thin, microscopic, thread-like tubules.
Sporangia – structures that hold spores.
Reproduction
Asexual – by means of formation of spores, a process known as sporulation.
Sexual – by means of formation of a diploid zygospore.
Picture
Laboratory procedures when handling microorganisms:
Use aseptic technique: procedure where contact with, or contamination by, microorganisms is avoided.
Always wear a lab coat.
Wash your hands before and after the experiment.
Wear protective gloves where appropriate.
Wear safety glasses where appropriate.
Keep your hands away from your face at all times in the laboratory.
Clean the bench thoroughly before and after use and swab with disinfectant, such as 70% ethanol or Milton.
Clean and sterilise all glassware involved in the experiment before and after use by placing in an autoclave or a pressure cooker for 15 minutes.
When using Petri dishes and containers to grow microorganisms, only open very slightly and for the shortest possible time to avoid contamination.
If using forceps or an inoculating loop, use a Bunsen flame to sterilise before and after use.
Practical activity: to investigate the growth of leaf yeast using agar plates and controls.
Follow aseptic technique as described above.
Make up a 1.5% solution of agar (1.5 g agar in 100 ml distilled water).
Sterilise by boiling the agar solution.
Carefully pour the agar into three Petri dishes and allow to set solid.
Obtain old leaves from your local park.
Disinfect one of the leaves (this acts as a control).
Attach this leaf to the inside of the lid of one Petri dish using some petroleum jelly and ensuring the underside of the leaf is facing the agar.
Attach the test leaf (not sterilised) to the inside of the lid of the other Petri dish.
Ensure neither leaf is touching the agar.
Leave the third Petri dish closed – this acts as a negative control.
Seal the dishes shut using parafilm.
Leave the dishes upside down in the incubator set at 25˚C for 3 days.
Result:
Pink colonies form on the agar of the test.
The controls showed no growth of leaf yeast.