Kingdom Protista is a diverse group of eukaryotic organisms. Protists are unicellular, some are colonial or multicellular, they do not have specialized tissue organization. The simple cellular organization distinguishes the protists from other eukaryotes. The cell body of the protists contain have a nucleus which is well defined and membrane bound organelles. Some have flagella or cilia for locomotion. Reproduction in protists is both asexual and sexual. They live in any environment that contains water.

 

 

Characteristics of Kingdom Protista

General characteristics of Kingdom Protista are as follows: 

• They are simple eukaryotic organisms.

• Most of the organisms are unicellular, some are colonial and some are multicellular like algae.

• Most of the protists live in water, some in moist soil or even the body of human and plants.

• These organisms are eukaryotic,  since they have a membrane bound nucleus and endomembrane systems.

• They have mitochondria for cellular respiration and some have chloroplasts for photosynthesis. 

• Nuclei of protists contain multiple DNA strands, the number of nucleotides are significantly less than complex eukaryotes.

• Movement is often by flagella or cilia.

• Protists are multicellular organisms, they are not a plant, animal or fungus.

• Respiration - cellular respiration is primarily aerobic process, but some living in mud below ponds or in digestive tracts of animals ares strict facultative anaerobes.

• Nutrition - they can be both hetreotrophic or autotrophic. 

• Flagellates are filter feeding, some protists feed by the process of endocytosis (formation of food vacuole by engulfing a bacteria and extending their cell membrane).

• Reproduction - some species have complex life cycle involving multiple organisms. Example: Plasmodium. Some reproduce sexually and others asexually. 

• They can reproduce by mitosis and some are capable of meiosis for sexual reproduction.

• Some protists are pathogens of both animals and plants. Example: Plasmodium falciparum causes malaria in humans.

• Protists are major component of plankton.

Economic Importance of Protists

Protists are useful in the following manners:
Source of food - Some protists like kelps are edible.
Source of commercial products - Marine protists are source of useful substances like algin, agar, carragean and antiseptics.
Primary producer of aquatic ecosystem - Many protists are primary producers, they play a basic role in food cahins, providing food and oxygen.

Source of medicines - Sodium laminaria sulphate, Fucoidin, Heparin are algal products used as blood coagulants. Lyngbya produces an anti-cancer compound. 

Source of mineral - Kelps are rich in sodium, potassium, iodine etc, they are good source of minerals. 

Biological research - They are used in biological research, e.g., Chlorella is unicellular, non-motile alga.

Pathogens - Thhese ar pathogenic organisms and may cause many disease in man and also in fruits and vegetables it causes late blight potatoes and causes disease in some fishes.