Salient Features of Protista

Introduction

Protists comprise a huge collection of unicellular and multicellular organisms that have a nucleus. They also possess highly specialized cellular organs called cell organelles that help in performing various life processes. Most protists are free-living autotrophs (such as algae) while others are heterotrophic (such as amoeba) or even parasitic (such a Trypanosoma protozoa).

Protists have certain characteristics in common with animal cells and thereby they also have mitochondria, commonly called the powerhouse of the cell and provides energy for the cell. Protists which have common features with plant cells have a cell wall and chloroplasts. Photosynthesis is made possible in these cells through chloroplasts.

Example of Protista

The protists can be unicellular or multicellular organisms. Some common examples of Protista are Amoeba, Diatoms, Dinoflagellates, Plasmodium, etc.

Amoeba

The microscopic unicellular protozoans of the rhizopoda order Amoebida are termed as Amoeba. The commonly known species, Amoeba Proteus is generally found on decaying bottom vegetation of freshwater streams and ponds. Amoeba is simply described as a simple eukaryotic organism that moves in a characteristic crawling fashion.

Amoebas move from place to place using pseudopodia, which translates to “false feet”. These short-lived, outward projections of the cytoplasm, the semifluid material inside the cell membrane helps the amoebas to grab a surface and move themselves forward. With the movement of the pseudopodium out along a surface in one direction, the back end of the amoeba contracts.

Plasmodium

Plasmodium is unicellular eukaryotes that are obligate parasite or holoparasite of vertebrates and insects. The life cycles of Plasmodium species involve development in an insect feeding on blood which harbors a smaller organism and then injects parasites into a vertebrate host during a blood meal.

Parasites grow within a vertebrate body tissue (often in the liver) to infect red blood cells before entering into the stream of blood in the body. The destruction of host red blood cells can result in the disease called Malaria. During this infection, some parasites are picked up by an insect feeding on blood (mosquitoes in majority cases), continuing the life cycle. 

Over 200 species of Plasmodium have been discovered till date and many of which have been further divided into 14 sub-genes based on parasite morphology and range of host. Evolutionary relationships among different Plasmodium species do not obey taxonomic boundaries; some species that are morphologically similar or infect the same host turn out to be related distantly.

Wherever suitable hosts are found, species of Plasmodium are distributed globally. Insect hosts are most frequently mosquitoes belonging to the genera Culex and Anopheles. Hosts that are vertebrae include reptiles, birds, and mammals. Plasmodium parasites were first identified by Charles Laveran in the 19th century.

Diatoms

Diatom that belong to the class of Bacillariophyceae, means any member of the algal class Bacillariophyceae, with about 16,000 species that are found in sediments or attached to solid substances in all the waters parts of Earth. Diatoms are among the most important microscopic sea organisms and serve directly or indirectly to many animals for food. 

Diatoms may be either unicellular or multicellular. The cell wall composed of silica material forms a shell composed of overlapping halves (epitheca and hypotheca) perforated by intricate and delicate patterns. Food is stored as droplets of oil, and the golden-brown pigment masks the green pigment chlorophyll and pigments of carotenoid are also present. Diatoms are commonly segregated into two levels on the basis of structure and shape: the round non-moving Centrals which have radial markings and the elongated Pennales, which move with a gliding motion and have featherlike markings.

Dinoflagellates

Dinoflagellates are a group of single-celled eukaryotes constituting the phylum Dinoflagellata and usually considered in the group of algae. Dinoflagellates are organisms found mostly in marine but they cannot propel themselves during currents. They also are common in organisms that live in freshwater. Their populations differ with temperature of the sea surface, the saltiness in water, and depth. Many dinoflagellates are photosynthetic, but a large fraction of these are in real mixotrophic that means they combine photosynthesis with ingestion of prey rather than having a single mode.

In terms of number of species, dinoflagellates are one of the largest groups of marine eukaryotes, anyway substantially smaller than diatoms. Some species are endobiont, organisms that live on other organisms of marine animals and play an important part in the biology of coral reefs. Other dinoflagellates are non-pigmented predators on other protozoa, and a few forms are parasitic. Some dinoflagellates produce dinoflagellate cycles which are resting stages as part of their life cycles.

Salient Features of Protista

• Single cell colonial filamentous eukaryotes

• Humid and moist environment promotes the growth of protista

• Protista can vary as photosynthetic as well as non photosynthetic

• Live plants are included in forms of animals

• Examples include protozoa, slime moulds , Englenoids and Chrysophytes protistan algae

Diversity of Kingdom Protista

Protists have a nucleus containing their DNA like all other eukaryotes. They also have other membrane-bound organelles, such as mitochondria and the endoplasmic reticulum. Most protists are single-celled. Some are multicellular. Because of the diversity of Kingdom Protista, their ways of getting food and reproducing vary widely.

Protist Habitats

Protists are mostly organisms that live in aquatic environments. They need a moist environment for survival. They are found mainly in watery areas like damp soil, marshes, puddles, lakes, and the ocean. Some protists are free-living organisms that live on themselves. Others are involved in symbiotic relationships that is they live on other organisms, including humans.

Motility of Protists

The ability of the organisms to move is known as its mobility. Protists have three types of characters for movement, namely they may have flagella, cilia, or pseudopods (better known as false feet). There may be one or more whip-like flagella. Cilia are similar to flagella, except for the fact that they are shorter and there are more of them than in flagella. They may completely cover the surface of the cell of protists. Pseudopods are temporary and are foot-like extensions of the cytoplasm.

Protist Reproduction

Life cycles of the protists are complex. Many protists have both asexual and sexual reproduction. An example is a protist called Spirogyra which is a type of algae. It usually exists as cells that reproduce by the process of binary fission. In a disturbed environment, like one that is very dry, Spirogyra may produce tough spores that can help them to survive harsh conditions. Spores means the reproductive cells produced by protists and various other organisms. When two protist spores are kept close together, they can fuse to form a diploid zygote which is a type of sexual reproduction. The zygote then undergoes meiosis, producing cells that repeat the cycle.

Protist Nutrition

Protists get food there by ingestion, or absorption, or produce their own organic molecules.

Ingestive protists ingest, or consume, bacteria and other small particles present around. They extend their cell wall and cell membrane around the food item, forming a food vacuole. Then the vacuole helps them to digest the food.

Absorptive protists absorb food molecules around their cell membranes. This occurs by the process of diffusion. These protists are organisms that easily decompose and are thereby important decomposers.

For the production of food by themselves, protists use light energy by the process of photosynthesis. They in aquatic environments are important producers.

Conclusion

We have discussed the various salient features of Protista in this discussion. We have briefly explained how protists are a huge collection of unicellular or multicellular eukaryotes. Various examples of protists are discussed thereafter explaining how Amoeba functions. The use of false feet by Amoebas to catch their prey is also discussed for better understanding of the topics.  Protists also possess various characteristics features such as their ability to move, their feature of reproduction sexually or asexually.