Protists, Fungi and Lichens: Key Traits, Classification and Uses

Protists

Protists are eukaryotic organisms. They include protozoa and algae, most of which are unicellular. As eukaryotes, protists possess a membrane-bound nucleus (karyotheca) and membranous organelles.

Protozoa

Protozoa are eukaryotic, unicellular heterotrophs. Protozoa are classified by the organelles they use for locomotion:

• Rhizopods: move by means of pseudopodia. Example: Amoeba.
• Ciliates: move by means of cilia. Example: Paramecium.
• Sporozoans: have no locomotor structures, and parasitic protozoa lack organelles for movement. Examples: Plasmodium (malaria) and Toxoplasma gondii.
• Flagellates: move by means of flagella. Example: Trypanosoma cruzi (Chagas disease).

Algae

Algae are eukaryotic, unicellular autotrophs. They are found in various environments, such as lakes, rivers and oceans, and generally live in moist environments.

• Euglenophytes
• Chrysophytes: including diatoms.
• Pyrrophytes: including the organisms responsible for red tide.

Multicellular Algae

Multicellular algae are eukaryotic, multicellular autotrophs:

• Chlorophyta: green algae.
• Phaeophyta: brown algae.
• Rhodophyta: red algae.

Kingdom Fungi

Fungi can be unicellular or multicellular, and they are eukaryotic. They can be microscopic or macroscopic and live in humid environments and in places rich in organic matter. Fungi are heterotrophic decomposers of organic matter, feeding by absorption (extracorporeal digestion). They do not have chlorophyll and have cell walls made of chitin.

Fungi reproduce asexually by spores or sexually by the fusion of hyphae. Fungi are formed by hyphae, and the tangled mass of hyphae is called the mycelium. Wherever there is organic material, fungi may be found.

• Unicellular fungi: yeasts.
• Multicellular fungi: mushrooms and filamentous fungi (mycelium).
• Microscopic fungi: yeasts and filamentous fungi.
• Macroscopic fungi: ear fungi, mushrooms and coral fungi.

Industrial Uses of Fungi

• Bread making: yeasts (Saccharomyces cerevisiae).
• Cheese making.
• Production of alcoholic beverages.
• Medicine production: Penicillium notatum is the source of antibiotics.

Diseases caused by fungi include mycoses, thrush and athlete's foot (tinea pedis).

Lichens

Lichens result from a mutualistic association between fungi and unicellular algae or filamentous cyanobacteria (blue-green algae). They are indicators of air quality and are found on tree trunks.

Key Points

• The two main characteristics of protozoa: they are eukaryotic and unicellular.
• Classification of multicellular algae: chlorophytes, phaeophytes and rhodophytes.
• Diseases caused by protozoa: amoebic dysentery, malaria and toxoplasmosis.
• Red tide and the alga responsible: red tide is a population bloom of microalgae that occasionally occurs in certain locations on the water surface. The responsible organisms are pyrrophytes.