Kingdom protists

kingdom protista

1. You must have seen ponds covered with green plants. You always thought that those are mosses. Didn’t you? Well no! We will see what those are. It is time to peek deeper into another kingdom in this chapter: Protista . We will also take a look at their characteristics and examples . We place all single-celled eukaryotes under Protista. 

2. A protist is a group of eukaryotic organisms which are not classified as either an animal, plant or fungus. They possibly share certain morphological and physiological characteristics with animals or plants or both. The term protist typically is used in reference to a eukaryote that is not a true animal, plant, or fungus the cells of protists have highly organized nucleus and specialized cellular organelles. Some protists have flagella or cilia for locomotion. They inhabit an environment that contains water.

3. Characteristics of Kingdom Protista Protists are simple eukaryotic organisms. Most of them are unicellular , some are colonial and some are multicellular like algae but they do not have specialized tissue organization. Most of the protists live in water. Some live-in moist soil and even in the body of humans and plants. Like all eukaryotic cells, the protists also possess a characteristic central compartment called the  nucleus , where the genetic material is present.

4. They also have specialized cellular organelles that perform definite functions within the cell. Their nucleus is membrane bound. Nuclei of protists contain multiple DNA strands. Photosynthetic protists like various types of algae contain these organelles that are the site of photosynthesis (the process of harvesting sunlight to produce nutrients in the form of carbohydrates). The plastids of some protists are similar to those of plants.

5. Some protists that live in anoxic conditions (environments that lack oxygen) use an organelle called the  hydrogenosome  ( a modified version of mitochondria) for some of their energy production; for example, in  Trichomonas vaginalis .) In protists that have mitochondria, aerobic respiration takes place, the protists , that live in the mud below ponds or in digestive tracts of animals are strict facultative anaerobes, the respiration occurs with the help of hydrogenosome .

6. They form cysts in adverse conditions. When the protozoan parasites, are exposed to very harsh conditions during various stages in their life cycle, they form cysts around them. An encysted form allows them to survive in extreme conditions. Some protists are pathogens for both animals and plants. Example:  Plasmodium falciparum  causes malaria in humans. They show movement by flagella or cilia. Most protists have mitochondria (organelle which generates energy for cells to use).

7. Mode of Nutrition

8. Locomotion in Protists

9. Pseudopodia They are projections of the  cytoplasm  of  unicellular   protists or  eukaryotic cell  membrane. 

10. Lobopodia Lobopodia refer to the finger-shaped pseudopod and is the most common type observed in nature. They are characterized as short, blunt, and bulbous projections that contain both endoplasm and ectoplasm of the  organism . An example is the lobose amoebae, which is considered the largest of all pseudopodia.

11. Filopodia Characterized by having thin and thread-like pseudopod, filopodia has the ability to branch out or anastomose.   They are filiform and slender with pointed ends that are mostly made of ectoplasm. The projections are supported by microfilaments. Examples include Lecithium  and  Euglypha .

12. Reticulopodia Imagine pseudopodia being used as a means to communicate with other cells. Reticulopodia is a specialized pseudopod that communicates with another pseudopodium, thus creating a network called reticulum. Also called reticulosepseudopodia , they create complex projections wherein the individual pseudopodium fuses with one another to create what looks like irregular nets. This type of pseudopodium also functions in both ingestion of food and locomotion. Examples - Foramineferans .

13. Axopodia Axopodia are pseudopods supported by arrays of microtubules. The pseudopodia are enveloped by cytoplasm; thus, it is used most for  phagocytosis  or ingestion of food particles. Protists from the  genus   Radiolaria  and  Heliozoa  are examples of this type of pseudopodium.