Biological Classification — Visual Overview
Attribution: Wikimedia Commons — Lobaria pulmonaria (foliose lichen), CC BY-SA 3.0
The Five Kingdoms — Classification Flow
Sub-cellular Infectious Agents at a Glance
| Property | Virus | Viroid | Prion |
|---|---|---|---|
| Has nucleic acid? | Yes (DNA or RNA) | Yes (RNA only) | No |
| Has protein coat? | Yes (capsid) | No | Yes (misfolded) |
| Size relative | Largest of the three | Smaller than virus | Smallest |
| Causes disease in | Animals, plants, bacteria | Plants only | Animals only |
| Discoverer | Ivanowsky (TMV, 1892) | T.O. Diener (1971) | Prusiner (1982) |
Fungal Kingdom — Visual Organisation
| Phycomycetes | Ascomycetes | Basidiomycetes | Deuteromycetes |
|---|---|---|---|
| Coenocytic hyphae | Septate hyphae | Septate hyphae | Septate hyphae |
| Zygospores | Ascospores | Basidiospores | Conidia only |
| Aquatic/damp habitat | Diverse | Terrestrial | Diverse |
| Mucor, Rhizopus | Saccharomyces, Aspergillus, Neurospora, Claviceps | Agaricus, Ustilago, Puccinia | Alternaria, Trichoderma |
Lichen — Symbiosis Summary
A lichen is not a single organism — it is an intimate partnership between:
- Phycobiont (alga or cyanobacterium): performs photosynthesis, provides organic nutrients
- Mycobiont (fungus): provides structural support, absorbs water and inorganic minerals from the substrate
Three morphological types based on growth form:
- Crustose: Flat, crust-like, closely adhering to rock/bark
- Foliose: Leaf-like, lobed, loosely attached
- Fruticose: Shrub-like, branched, hanging or erect
Ecological significance: Lichens are pioneer colonisers of bare rock, initiating soil formation. Their extreme sensitivity to makes them invaluable air quality bioindicators.