fungi

• Fungi


  • Can be unicellular or multicellular
  • They are eukaryotic
  • Their cell wall contains chitin
  • They are heterotrophic
  • They reproduce by means of spores
• Fungi


  • field mushroom
  • toadstool
  • Athlete's foot
  • yeast
• Unicellular fungi


  e.g. Yeast
• Multicellular fungi


  e.g. Mushroom
• Multicellular fungi


  • Made of thread like structures called hyphae
  • A mass of hyphae is called a mycelium
  • They secrete digestive enzymes and then absorb the digested material (food)
• Saprophytes


  Feed on dead organic matter
• Parasites


  Feed on a live host
• Most fungi are saprophytic
• Fungi play a vital role in the environment as they are responsible for decay - decomposers
• Obligate parasites


  Live on live hosts but do not normally kill them
• Facultative parasites


  Kill the host and feed on the remains
• Lichens


  • An organism which is a combination of a fungus and an algae
  • The fungus gives the algae shelter, and the algae supply the fungus with food, which they produce by photosynthesis
  • Lichens are good bioindicators of air quality as they only grow in clean air
• Every year people die in the pursuit of edible wild mushrooms
• Very many species of mushrooms are poisonous and can cause death
• Symptoms of Death Cap poisoning

  • Dizziness, vomiting, diarrhoea and dehydration
  • Death usually occurs 6 days after consumption due to liver and kidney failure
• 0.5g of a Death Cap can kill 100,000 mice
• Rhizopus


  • The black bread mould (Rhizopus Stolonifer), normally called Rhizopus is a mould commonly found on stale bread and rotting fruit
  • Rhizopus is a saprophytic fungus – it secretes enzymes onto the bread and absorbs the digested material
• Rhizopus structure


  • Comprised of thread like structures called hyphae
  • Hyphae in a group is called a mycelium
  • Three types of hyphae: Stolons, Rhizoids, Sporangiophores
• Rhizopus hyphae


  • No cross walls – aseptate
  • Multinucleate
  • Each nucleus is haploid
• Rhizopus asexual reproduction


  1. Tip of sporangiophore swells to form a columella

  2. Columella produces numerous haploid spores (sporulation) by mitosis that are held in the sporangium

  3. Sporangium eventually dries out and burst, releasing hundreds of haploid spores

  4. Spores germinate, producing a hyphae that grows and forms a new organism
• Rhizopus sexual reproduction


  1. Requires a plus and a minus strain

  2. Hyphae from opposite strains grow close together, forming progametangia

  3. Nuclei from both hyphae move into the progametangia

  4. Cross-walls form to produce gametangia

  5. Walls of gametangia dissolve, producing diploid zygote nuclei

  6. A zygospore forms around the nuclei

  7. When conditions are suitable, the zygospore germinates by meiosis, producing a hypha that grows out and produces a sporangium at the tip
• Yeast


  • The most frequently encountered yeast is baker's yeast or brewer's yeast – Saccharomyces Cerevisiae
  • Yeast is a unicellular fungus
  • The cells are eukaryotic
  • Its cell wall contains the carbohydrate chitin
  • There are many storage vacuoles in the cytoplasm along with one large vacuole
• Yeast respiration


  1. Obtains energy in anaerobic respiration – breaks down sugars (glucose) into alcohol and carbon dioxide

  2. Carbon dioxide used to cause bread and cakes to rise

  3. Ethanol is the alcohol found in beers and wines
• Yeast reproduction


  1. Reproduces asexually in a process called budding

  2. A swelling called a bud forms at one end of the cell

  3. The nucleus and vacuole split in two, one of each part moves into the bud

  4. Bud eventually separates from the parent cell
• Yeast is used in the baking and brewing industries
• Mushrooms are a source of food
• The antibiotic penicillin, is derived from Penicillium notatum
• There are other fungal based antibiotics such as streptomycin and erythromycin
• Pathogenic fungi can cause human disease. Examples include Athlete's foot, ringworm, nail fungus and thrush
• Fungi can cause food to spoil e.g. Rhizopus on bread or fruit
• Fungal infection can destroy crops. e.g. the Great Famine was caused by the potato – blight fungus which infected the potato crop
• Experiment: To investigate the growth of leaf yeasts

  1. Collect leaves, handling as little as possible

  2. Wash and disinfect the bench and your hands

  3. Place two malt agar plates on the bench, label 'A' and 'B'

  4. Place plate 'A' upside-down on the bench

  5. Flame the forceps and allow to cool

  6. Carefully raise the base of the petri dish just enough to work with

  7. Use the forceps to attach a leaf disc to each blob of petroleum jelly on the lid

  8. Seal the plates with parafilm, label and date

  9. Store all petri dishes right way up in an incubator at 20°C for 24 hours

  10. Turn the petri dishes upside down and incubate at 20°C for 3 days

  11. Sterilise the dishes before disposal
• Many microorganisms are pathogenic (disease causing)
• Sterile


  Free from unwanted microorganisms
• Asepsis (Aseptic Techniques)


  Measures taken to remove unwanted microorganisms