Protists are the first eukaryotes to evolve about 1000 million years back. Protists are all unicellular and colonial eukaryotes except green and red algae. They are broadly divided into- photosynthetic, slime moulds and protozoans.
Leeuwenhoek was the first to see and sketch protozoan’s protists including Vorticella and Giardia.
Characteristics of protists are:
*They are solitary unicellular, colonial unicellular, eukaryotic organism.
*They are mostly aquatic organism.
*A well defined nucleus (uninucleate, binucleate or multinucleated). Genetic material is RNA, enclosed by nuclear envelope, complexed with protein with distinct chromosome.
*Almost 95% of the protists are consisting of phytoplankton and 80% of the total photosynthesis is carried out by photosynthetic protists.
*If cell wall is, it is made up of cellulose.
* Cytoplasm contains ribosomes, a variety of organelles such as mitochondria, plastid, lysosome, cytoskeleton, endoplasmic reticulum and Golgibodies. Some contains centriole and ribosomes are 80S and 70S.
*Cytoplasm is always in motion which is called cytoplasmic streaming or cyclosis.
*Locomotory organs are flagella, cilia, pseudopodia contractions, mucilage and extrusion.
*Food reserve is starch, glycogen, paramylon, chrysolaminarin and fat.
*Asexual reproduction is quite common and occurs through budding, binary fission, multiple fission, plasmotomy, sporulation, Cyst formation etc.
*Sexual reproduction occurs with the help of nonjacketed gametangia by meiosis and karyogamy.
*Three types of life cycle occur in protists are- plant, animal and fungal.
*Protistans serve as the linkage between monerans and rest of the kingdom.
*Mitotic apparatus is formed during cell division.
*No embryo is formed.
Protists can be divided into-
1. Euglenophyta - This include Euglinoids organism. This phylum category includes flagellate protists of freshwater, damp soils. Previously they were included in phytomastigophora by zoologist. They have tinsel and tactellum type of flagellum with the roots developing from an invagination and an eye spot nearby. E.g. Euglena, Paranema, Phacus, Rhabdomonas.
2. Xanophyta-This phylum includes yellow green algae.
3. Chrysophyta- They are also called Golden algae. This phylum includes Chrysophyceae and Bacillariophycea.
4. They are also called Dinophyceae (dinoflagellate), Cryptomonads. They include golden brown photosynthetic protists and have two flagella. E.g. Noctiluca, Gonyaulax, Gymnodinium, Ceratium.
5. Hypochytridiomycota- They includes Hyphochytrids. Included in slime moulds.
6.Plasmodiophoromycota - The phylum includes plasmodiophores. They are also included in slime moulds.
7. Sporozoa- The phylum includes sporozoans. Malarial parasites Plasmodium are example of sporozoans.
8. Cnidosporidia- This group of protozoans are able to form spore that covered by wall.This include cnidosporidia-. E.g. Myxosporidia, Microsporidia.
9. Zoomastigina- This phylum contains zooflagellates means this protistans protozoans contain flagella as their locomotory organ. It is then categorize according to number of flagella.E. g Trichomonas, Giardia, Lophomonas.
10. Sarcodina- organismsof sarcodina contains pseudopodia. According to presence of pseudopodia it can be divided into different category. E.g. amoebids, heliozoans, foraminiferans, radiolarians.
11. Ciliophora - This phylum includes cilia as their locomotory organs. E.g. Vorticella, Paramecium, Balantidium.
Short Questions and answers on Kingdom Protista:
1. What is capillitium?
Sterile threads in sporangia of acellular slime moulds for dispersal of spores.
2. What is pyrenoids?
In euglinoids, chloroplast contains a proteinaceous body called pyrenoids.
Which is called consumer decomposer protists?
Slime moulds due to feeding on microorganisms and decaying organic matter through ingestion.
3. What is Hydramoeba?
Ectoparasitic protozoans protists feeding on epidermal cells of Hydra is called Hydramoeba.