- All fungi are heterotrophic.
- They can besingle-celled (e.g. Yeasts) or multicellular (e.g. mushrooms).
- 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.
- There are two types of heterotrophic nutrition in fungi:
- 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’ – a small swelling forms on the cell; it fills with cytoplasm and the nucleus divides by mitosis with one of the resulting nuclei moving into the ‘bud’.
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.
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.
- Agar powder
- Hotplate/ heating equipment
- Petri dishes
- Ash leaves
- Petroleum jelly
- Lab coat and safety goggles and gloves
- Follow aseptic technique as described above.
- Make up a 1.5% solution of malt agar (1.5 g agar in 100 ml distilled water along with a teaspoon of malt). [NOTE: Leaf yeast will not grow without a source of maltose]
- Sterilise by boiling the agar solution.
- Carefully pour the agar into three Petri dishes and allow to set solid (~10 minutes)
- Obtain old Ash leaves from your local park. [NOTE: September/October is the best time of year to do this activity, as the leaf yeast have had the spring and summer months to reproduce on the leaves).
- Disinfect (by rubbing with alcohol or sterilising fluid) 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 24 hours and then turn them right side up for the remaining few days (4-6 days).
- Pink colonies form on the agar of the test.
- The controls showed no growth of leaf yeast.
- Leaf yeast grow best on the underside of a leaf – as they are not washed off by rain or damaged by UV light.
- Leaf yeast live in larger numbers on older leaves as they have had the spring and summer months to grow and multiply.