Organisms of the kingdom protista

Protista organisms can be classified according to:

• Type : can be protozoa or algae
• Size: can be microscopic or macroscopic
• Diet: heterotrophs (organic matter) or autotrophs (photosynthesis)
• Cell formation: they can be unicellular (one cell) or multicellular (several cells)

Algae: general characteristics

For a long time, algae were considered to be plants, due to their characteristics in common with vegetables. However, they are currently considered to be part of the kingdom Protista.

Although algae can carry out photosynthesis, they are distinguished from plants because:

• They do not have proper tissues and, although some algae are multicellular, there are also other types that are unicellular.
• Algae can live fixed in one place or be mobile.
• Although their cells are similar to those of plants because they have a nucleus and chloroplasts, the composition of their cell wall is different.
• Not all algae use chlorophyll in the process of photosynthesis. Some types use pigments, so you can find algae of different colors besides green, such as black, red, brown, and others.

Habitat and reproduction

Algae generally live in aquatic environments such as seas, oceans, and lakes. Others can even live in rocks or damp wood or inside other organisms such as mollusks, corals and plants.

As for the reproduction of algae, it can be sexual or asexual. Sexual reproduction occurs through the union of male and female gametes, as occurs in other living beings. The asexual reproduction of algae is carried out by fragmentation. This occurs when a fragment of the thallus, which is a multicellular formation, breaks and a new one emerges from each part.

Protozoa: general characteristics

The name protozoan derives from the Greek terms proto “first”, and zoo , “animal”, because animals are believed to have arisen from the evolution of these organisms. In fact, their cells are very similar to those of animals and are eukaryotic, unicellular and mobile organisms. Most of them are microscopic and need water to survive. Therefore, they are also found in aquatic habitats.

According to their mobility, we can divide them into:

• Ciliates: they are the most complex protozoa. They use cilia to transport themselves. An example of this type of protozoa is the paramecium.
• Sarcodins: they move using pseudopods, which are extensions of the same cell. An example of this type is the amoeba.
• Flagellates: they have flagella and use them to move. The most common example is the Trypanosoma parasite , which causes sleeping sickness.
• Immobile – these are parasites. The most common is plasmodium , which causes malaria, or paludism.

Feeding and reproduction

Protists are heterotrophs, that is, they feed on organic matter. Its feeding is produced by phagocytosis: the protozoan membrane surrounds the substance that it is going to ingest, locking it inside to degrade it.

The reproduction of protozoa is asexual. It can be by budding, bipartition or sporulation. However, there are also some that reproduce sexually.

plankton

Plankton is made up of algae and protozoa. They are small organisms that live in water.They can be divided into two types: phytoplankton, which carry out photosynthesis; and zooplankton, which feed on phytoplankton.

Heterotrophic and autotrophic protists

Another classification of protists is based on their diet:

• The heterotrophic protists :
  • They are microscopic, unicellular and heterotrophic organisms.
  • They feed on bacteria, remains of organisms, and other microscopic organisms.
  • They live in aquatic environments.
  • Most are free-living, but there are some parasites, example:  Trypanosoma cruzi .

• Autotrophic protists :
  • They have cells similar to those of plants, since they have chloroplasts and a cell wall.
  • Most are unicellular and constitute phytoplankton (microscopic, photosynthetic , aquatic, free-living organisms).
  • All its cells have the same appearance and perform the same functions.
  • Depending on the pigment they possess, they can be classified into green, brown and red.
  • They live in freshwater or marine habitats. They are also present in habitats with high moisture content such as forests.

Other examples of protists

• Algae, amoebas, euglena, and slime molds are some of the protists that can carry out photosynthesis .
• Amoebas are amorphous and move using pseudopods.
• Fire algae: These are plankton that can reproduce quickly and produce harmful blooms.
• Diatoms are some of the single-celled algae known as phytoplankton.
• Sporozoans: they are parasites that cannot move. They reproduce by forming spores. Examples of sporozoans are the plasmadium and the sporozoan  Toxoplasma gondii  which causes the disease toxoplasmosis.
• Trypanosomes move by means of  flagella .
• Paramecia use cilia to move. The cilia are thread-like protrusions that extend from the body and perform a kind of sweep.
• Slime molds: they can be plasmodial or cellular.
• Oomycetes: They are a species of aquatic mold. They have a cell wall made of cellulose and can reproduce sexually or asexually.

Bibliography

• Mikoley, K. What are protists? (2020). USA. Gareth Stevens.
• Lopez-Ochoterena, E.; Serrano-Limón, G. The wonderful world of protozoa. (2005). Mexico. Journal of the Mexican Society of Natural History, 2(1): 231-237.
• Sleigh, MA Biology of the Protozoa . (1973). Madrid. Blume.