Chapter 21: Kingdom Fungi
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)
- Cell wall made of chitin
- Granular cytoplasm
- Asexual by mitosis in a process known as ‘budding’.
Rhizopus (Common bread mould)
- Cell wall made of chitin
- Hyphae – thin, microscopic, thread-like tubules.
- Sporangia – structures that hold spores.
- Asexual – by means of formation of spores, a process known as sporulation.
- Sexual – by means of formation of a diploid zygospore.
- 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.
- Pink colonies form on the agar of the test.
- The controls showed no growth of leaf yeast.