Kingdom Protista

Kingdom Protista is a diverse group of organisms. It includes all eukaryotes that aren't animals, plants, or fungi, including single-celled and multicellular creatures. There are an estimated 60,000 to 200,000 protist species, with many more yet to be discovered. Apart from a relatively simple organization, the eukaryotes that make up this kingdom have little in common. Some protists are small and unicellular, like an amoeba, while others, like seaweed, are enormous and multicellular. Multicellular protists, on the other hand, lack highly specialized tissues and organs. Protists are distinguished from other eukaryotes, such as fungi, mammals, and plants, by their basic cellular arrangement. Protista is largely an aquatic phylum. This kingdom is linked to the kingdoms of plants, animals, and fungus.

The Protista cell body, like other eukaryotes, has a well-defined nucleus and other membrane-bound organelles. Some have flagella or cilia, while others don't. Cell fusion and zygote development are used by protists to reproduce both asexually and sexually. Many protists, such as algae, are photosynthetic and play an important role in ecosystems as primary producers. Other protists cause a variety of deadly human diseases, including malaria and sleeping sickness.Chrysophytes, Dinoflagellates, Euglenoids, Slime molds, andProtozoans come under Protista.

A. Chrysophytes:

Diatoms and golden algae (desmids) are members of this category. They can be found in both freshwater and marine habitats. They are tiny and float on water currents passively (plankton). They are mostly photosynthetic. The cell walls of diatoms produce two thin overlapping shells that fit together like a soapbox. Because the walls are embedded with silica, they are unbreakable. As a result, diatoms have left behind a vast amount of cell wall deposits in their habitat, which has been referred to as 'diatomaceous earth' over billions of years. Because this soil is rough, it is utilized for polishing and filtration of oils and syrups. In the oceans, diatoms are the primary 'producers.'

Figure 4: Diatoms observed under a light microscope.

B. Dinoflagellates:

These organisms are mostly marine and photosynthetic.They appear yellow, green, brown, blue, or red dependingon the main pigments present in their cells. The cell wallhas stiff cellulose plates on the outer surface. Most ofthem have two flagella; one lies longitudinally and theother transversely in a furrow between the wall plates.Very often, red dinoflagellates (Example: Gonyaulax)undergo such rapid multiplication that they make thesea appear red (red tides). Toxins released in such largenumbers may even kill other marine animals such as fish.

Figure 5: Dinoflagellates.

C. Euglenoids:

The majority of them are freshwater organisms found in stagnant water. Instead of a cell wall, they have a protein-rich layer called pellicle which makes their body flexible.They have two flagella, a short and a long one. Thoughthey are photosynthetic in the presence of sunlight, whendeprived of sunlight they behave like heterotrophs bypredating on other smaller organisms. Interestingly, thepigments of Euglenoids are identical to those present in higher plants. Example: Euglena.

Figure 6: Euglena

D. Slime Molds:

Slime molds are protists that feed on their surroundings. The organism eats organic matter as it glides along with rotting twigs and leaves. They create a plasmodium, which can grow and spread over severalfeet if the conditions are right. The plasmodium develops and generates fruiting bodies with spores at their tips in unfavorable conditions. True walls exist within the spores. They are highly hardy and may live for many years in harsh environments. Air currents disseminate the spores.

Figure 7: A slime mold.

E.Protozoans:

They are all heterotrophic organisms that exist as predators or parasites. Animal relatives are thought to be their ancestors. Protozoans are divided into four categories.

1. Amoeboid protozoans dwell in freshwater, seawater, or moist soil. As in Amoeba, they move and seize their prey by putting out pseudopodia (false feet). Silica shells cover the surface of marine organisms. Some of them are parasites, such as Entamoeba.

2. Flagellated protozoans: This group includes both free-living and parasitic protozoans. They have flagella on their bodies. Sleeping sickness is caused by a flagellated parasitic protozoan. Trypanosoma is a good example.

3. Ciliated protozoans: Ciliated protozoans are aquatic, actively moving organisms with thousands of cilia. They have a cavity (gullet) on the cell surface that opens to the outside. The water-containing food is directed towards the gullet by the coordinated movement of rows of cilia. Paramoecium is a good example.

4. Sporozoans: This term refers to a group of organisms that have a spore-like stage in their life cycle. Plasmodium (malarial parasite), which causes malaria, is the most well-known. Malaria is a disease that has a devastating impact on the human population

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Figure 8 (a) Ameoba (b) Trypanosoma (c) Paramecium (d) Plasmodium