Biology of Kingdom Protoctista: Protozoa and Algae

Kingdom Protoctista: Eukaryotic Organisms

Protoctists are eukaryotic organisms with a nucleus containing genetic material and cytoplasmic organelles. They live in aquatic environments, humid areas, or internal liquids.

Protozoa: Heterotrophic Organisms

Protozoa are mobile, heterotrophic organisms. They primarily use asexual reproduction, although sexual phenomena exist for the exchange of genetic information between members. Some present forms of resistance, such as cysts and spores, to survive. They are classified into four phyla according to their locomotion and lifestyle:

• Sarcodina: They use pseudopods and are mostly free-living, such as amoebae.
• Flagellates: They use flagella; some are photosynthetic. An example is Trypanosoma gambiense.
• Ciliates: They have cilia arranged in formations with several functions, including locomotion and feeding. They usually have two nuclei and are free-living, such as the Paramecium.
• Sporozoans: They lack structures for locomotion and are all parasites.

Unicellular Algae

Unicellular algae have chloroplasts with chlorophyll and other pigments, along with a cellulose cell wall. All are aquatic and are the main component of plankton. They utilize asexual and sexual reproduction with a haploid biological cycle. This group includes diatoms.

Multicellular Algae

Multicellular algae have a simple organization known as a thallus (talo). Living in aquatic or wet environments, they obtain all substances and pigments for photosynthesis. They contain chlorophyll and other photosynthetic pigments, a cellulose cell wall, and starch molecules as energy reserves. They live in shallow waters because they need light for photosynthesis. Reproduction is both sexual and asexual. Depending on their habitat, the dominant pigments change. They are classified as:

• Green algae (Chlorophyta): Found in marine and freshwater. Their primary pigment is chlorophyll. They are believed to be the origin of higher plants. An example is sea lettuce.
• Brown algae (Phaeophyceae): Marine organisms containing fucoxanthin, a brown pigment that allows for light gathering at greater depths. An example is Fucus.
• Red algae (Rhodophyta): Marine organisms found at greater depths. They possess phycoerythrin, a red pigment. Their cell membranes become impregnated with calcium salts, giving them great consistency. Due to their branched thallus, they are sometimes called coralline algae.

Slime Molds

All slime molds are heterotrophic and reproduce by spores.