Kingdom Protista

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Introduction

Kingdom Protista is composed of eukaryotic organism that can be unicellular or multicellular. They are heterotrophic which means they eat other organisms for their food. They are unicellular or multicellular. They have cell walls and nucleus. Protista include organisms in their kingdom that have a variety of life styles, feeding habits, reproduction methods and cell structure. They are the simplest of all the eukaryotic organisms. They are found in variety of places. They are found in soil, water and air.

Classification of Protista

On the basis of locomotry organs kingdom protista is divided into five major groups:

  • Chrysophytes
  • Dinoflagellates
  • Euglenoids
  • Slime Moulds
  • Protozoans

Chrysophytes

Chrsophytes are also known as diatoms and golden algae. The chrysophytes are a group of unicellular green algae. They occur in freshwater lakes and ponds, as well as in marine environments. Their chloroplasts are arranged in circular patterns. They are plant-like in that they contain an internal membrane system. The chrysophytes are found in freshwater lakes and ponds. They are also found in marine environments. They are found in temperate environments. They are autotrophs, meaning they can produce their own food. They use the process of photosynthesis to make food. Some of them will photosynthesize at night whilst others will photosynthesize during the day. They are the primary producers of the ocean.

Dinoflagellates

Dinoflagellates are unicellular and colonial marine planktonic eukaryotes. They are a part of the phylum Dinoflagellata and are commonly found in the waters of the ocean, lakes, and rivers. However, these organisms may also be found in soil and fresh water.

Dinoflagellates can be found in a variety of colors. Species are typically red, pink, orange, yellow, green, or brown. These organisms may have anywhere from one to several thousand flagella. The flagella are used to propel these organisms through the water. Dinoflagellates contain chloroplasts. Dinoflagellates have a cell wall made of cellulose. The cell wall helps protect these organisms from the environment. These organisms have a cell membrane composed of phospholipids and sterols. This membrane helps regulate what goes in and out of the cell.

Euglenoids

Euglenoids are a diverse group of flagellated protists found in a wide range of environments. Their defining feature is their large, highly refractive, and complex eye spot, called the macronucleus. Eyespots are found in the majority of euglenoids, though they are absent in certain species. The macronucleus is a large spherical cell, which contains a multitude of smaller eyespots, called micronuclei. The macronucleus is used to determine the direction of light, which is then relayed to the flagellum via a unique system of photoreceptors. The flagellum then moves in a way that is optimized for the organism’s environment. Euglenoids are usually found in freshwater environments, though many species are found in marine or brackish waters. They are either free-living or parasitic.

Slime Moulds

Slime moulds are eukaryotic organisms that belong to the group of amoebozoa and are non-cellular. The body of the slime mould is soft and pliable, consisting of a mass of protoplasm containing many nuclei. Slime moulds are heterotrophs and feed on decaying organic matter. They are also known to prey on microorganisms, using the amoeboid stage to engulf them and then digest them. Some of the slime moulds are pathogenic while some are used in the preparation of some medicines and food. Slime moulds are able to demonstrate various complex behaviors. Some of these behaviors include formation of fruiting bodies and plasmodium.

The lifespan of a slime mould is usually short. However, in unfavorable conditions the life cycle can be prolonged. The growth rate of slime moulds is determined by the availability of food. In favorable conditions, the life cycle of slime moulds can be as short as a few days.

Protozoans

Protozoans are one of the simplest forms of life. A protozoan consists of a single cell. The cell consists of protoplasm surrounded by a cell wall. The cell is bounded by a plasma membrane. The protozoan moves by means of flagellum. The flagellum is a very long cilium that is attached to the cell. The flagella allows the protozoan to swim. They move by propelling the cell forward by means of the flagellum. They move by beating their flagella.

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