give a brief description about protista
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Answer:
Protists are eukaryotic organisms that cannot be classified as a plant, animal, or fungus. They are mostly unicellular, but some, like algae, are multicellular. Kelp, or 'seaweed,' is a large multicellular protist that provides food, shelter, and oxygen for numerous underwater ecosystems.
KINGDOM PROTISTA
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.
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.
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 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.
They show movement by flagella or cilia.
Most protists have mitochondria (organelle which generates energy for cells to use). 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.
The mode of nutrition can be either heterotrophic or autotrophic in protists.
Some protists feed by the process of endocytosis (formation of food vacuole by engulfing a bacterium and extending their cell membrane) for example in case of Amoeba.
Mode of reproduction in protists is both asexual and sexual. They can reproduce by mitosis and some are capable of meiosis for sexual reproduction.
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 human.
The kingdom Protista is divided into three groups:
Animal-like protists: They are heterotrophs and have the ability to move.
Plant-like protists: They are autotrophs and have the ability photosynthesize.
Fungi-like protists: They are heterotrophs. Their cells have cell walls and have the ability to reproduce by forming spores.