Fungi and Protists
Beyond Animals and Plants
Fungi
Fungi are eukaryotic heterotrophs that absorb nutrients from organic matter. Key features:
- Body = mycelium (mass of hyphae = thread-like filaments)
- Cell walls made of chitin (not cellulose like plants)
- Saprotrophic: decomposers; also parasites and mutualists (e.g., mycorrhizae, lichens)
- Reproduce sexually and asexually via spores
- Major groups: Ascomycetes (sac fungi — yeasts, morels), Basidiomycetes (club fungi — mushrooms), Zygomycetes (bread mould)
Fungi are essential decomposers cycling nutrients, and commercially important (penicillin, bread, beer, cheese).
Protists
Protists are a paraphyletic assemblage — the catch-all kingdom for eukaryotes that are not plants, animals, or fungi. They include:
- Protozoa (animal-like): amoeba, paramecium, Plasmodium (malaria parasite)
- Algae (plant-like): diatoms, green algae, dinoflagellates — photosynthetic, major O₂ producers
- Slime moulds (fungus-like): aggregate into multicellular slug forms
Protists are ecologically vital — marine algae produce ~50% of Earth's oxygen.
Which polysaccharide makes up the cell walls of fungi?
Fungi have cell walls of chitin — the same polymer found in arthropod exoskeletons. Plants use cellulose; bacteria use peptidoglycan.
Correct answer: Chitin
Plasmodium falciparum, the malaria parasite, belongs to which group?
Plasmodium is an apicomplexan protozoan — a complex single-celled eukaryotic parasite. Malaria is NOT caused by a bacterium or virus.
Correct answer: Protists (protozoa)
Explain why fungi are classified as heterotrophs rather than autotrophs, and how they obtain nutrition.
Fungi = saprotrophic absorbers, not photosynthesisers.
Correct answer: Fungi cannot photosynthesise — they lack chloroplasts and cannot make their own food. They are heterotrophic absorbers: they secrete digestive enzymes (extracellular digestion) into organic matter (dead organisms, food, etc.) and absorb the resulting simpler molecules through their hyphae.