PROTISTA: EASY WAY TO EXPLAIN UNICELLULAR EUKARYOTES
INTRODUCTION: The kingdom protista includes diverse kinds of unicellular, eukaryotic micro-organisms which are predominantly water dwelling. Phylogenetically this kingdom links prokaryotic kingdom monera with the multicellular kingdoms Plantae, Fungi and Animalia. The protistan organisms exhibit various kinds of distinct life styles, which resemble with those of the plants, fungi and animals. Some of them bear chlorophyll and photosynthetic in naure like unicellular algae. Some are saprophytic living on dead and decaying organic matters like fungi. Some plants, fungi and aimals have evolved from protists like ancestors.
HABITAT OF PROTISTA: These are cosmopolitan in distribution. The photosynthetic protists are found in fresh water and ocean alike, where they occur as phytoplankton. These execute as chief producers in aquatic food chains. Some protists live as parasites in or on the bodies of other organisms. Some are found in the digestive tract or gut of insects like termites and cockroaches. Some protista are present on decaying organic matter.
STRUCTURE OF A TYPICAL PROTISTA: A protista has a typical eukaryotic cell. It possesses membrane bound distinct organelles like nucleus with nuclear membrane and nucleolus, mitochondria, endoplasmic reticulum, golgii complex etc. Besides, these organelles. The protists may possess flagella or cilia for locomotion. The flagella or cilia have 9+2 internal microtubular organisation. Photosynthetic protista forms contain chloroplasts and distinct wall.
LOCOMOTION OF PROTISTA : These animals show locomotion by three different kind of structure, i.e. flagella, cilia and pseudopodia. Some protists exihibit locomotion by wriggling or mucilagepropulsion.
By Flagella: The flagella are long thread like structures which help in moving the organism in water. The whip like action of flagella helps to propel the organism in water. This type of locomotion occurs in dinoflagellates, euglenoids and zooflagellated. The rate of locomotion is 15-300µm per second .
By cilia: The cilia are fine vibratile threads which are smaller but numerous as compared to flagella. Cilia beat in coordinated maner to propel the organismi in water like many person rowing a boat. This enables the organism to move rapidly, turn, tumble and even reverse. Ciliary locomotion is found ciliates, which are fastest predatory protista. This type of locomotion occurs at the rate of (400-200)µm per second.
By Pseudopodia: The Pseudopodia or false feet are the protoplasmic outgrowths of some protists like Amoea. They help the protsts in slow creeping ype of locomoion. Pseudopodial locomotion is found in sarcodines and slime moulds.
Types of pseudopodia
Broad and Blunt Lobopodia
Slender with support of axial filament Axopodia
Slender branched and reticulate Reticulopodia
With the help of mucilage secretion some protista like diatoms move by secreting mucilage. In which direction the mucilage direction occurs, opposite to that movement of protista occurs.
NUTRITION IN PROTISTA
They have diverse types of nutrition like,
- PHOTOSYNTHETIC or HOLOPHYTIC: Several of protists possess chlorophyll and prepare their food from carbon di oxide and water utilizing sunlight by the process of photosynthesis. Examples of protista doing photosynthesis are dinoflagellates, diatoms and euglenoids.
- HOLOZOIC or ZOOTROPHIC (INGESTIVE PHAGOTROPHIC): A number of protists capture and ingest food like animals e.g. many protozoans like Amoeba, Paramacium.
- SAPROBIC or SAPROTROPHIC (OSMOTROPHIC): Some protists like slime moulds obtain their food from decaying organic matter. After that whole body surface of protista absorbs these products.
- PARASITIC : This type of organisms obtain food from other organisms body. The individual which obtain food from the other organisms is called parasite and the organism from which parasite gets food is called host i.e. Trypanosoma, Giardia, Entomoeba, Plasmodium.
- MYXOTROPHIC: it is a mixed type of nutrition in which organisms can have two types of nutrition. For example, in Euglena is both holophytic and saprophytic.
REPRODUCTION IN PROTISTA
- Fission: In this method of reproduction the parent body split into two or more daughter cells. Each daughter cell receives a nucleus a nucleus by mitotic division. When cell splits into two daughter cells, the process is called Binary fission. Splitting of a cell into numerous daughter cells simultaneously we term as Multiple fission.
- Cyst formation: Under unfavorable condition such as drought, scarcity of water, some protists secrete a thick resistant covering to form a structure called cyst. In a cyst the cell become metabolically out of it. The cyst formation is helpful in dispersal as well as to pass over the unfavorable conditions. Many protozoal diseases like amoebic dysentery are spread by way of cyst.
It involves two fundamental processes i.e.
- Meiosis: That reduces the chromosome number from diploid (2N) to haploid (N)
- Syngamy or Fertilization: The fusion of two haploid (1N) gametes or sex cells to form a diploid (2N) zygote. In certain forms such as Paramecium only the fusion of nuclei takes place to form a diploid zygote nucleus. We term it as conjugation.
MAJOR GROUPS OF PROTISTA
It includes following major groups
Photosynthetic protists- the protistan algae
Slime moulds – The consumer decomposer protists
- PHOTOSYNTHETIC PROTISTS or PROTISTAN ALGAE: They possess cellulose wall in the form of distinct interlocking plates giving them an armored appearance which term as theca or lorica. Most species have brown, green or yellow chromotophores with chlorophyll a, chlorophyll c, ἀ carotene, Xanthophylls. In this group we can see diatoms and desmids or golden algae. These are an important food source for aquatic animals. Diatoms reproduces both asexually or sexually. It is considered that petroleum is probably the oil of the fossilized diatoms of the geological past.
- SLIME MOULDS or CONSUMER DECOMPOSER PROTISTA: They consist of a spreading slimy mass of protoplasm and share the character of both animals and fungi. Due to this peculiarity we term them fungus animals or mycetozoa. Acellular slime moulds have multinucleate protoplasm called plasmodium. It is covered with slime. Slime moulds have uninucleate haploid amoeba like cells into composite structure called PSEUDOPLASMODIUM. It is also known as grey or slug.
- PROTOZOAN PROTISTA : They are microscopic unicellular, free living or parasitic organisms. The body may be covered by a delicate membrane or pellicle or calcarious or silicious shell. They show holozoic, saprobic or parasitic nutrition. They form cysts during unfavourable periods of perennation. It includes some disease forming parasites.
Trypanosoma gambiens causes AFRICAN SLEEPING SICKNESS
Leishmania donovani causes KALA AZAR or DUMDUM FEVER
Giardia intestinalis causes GIARDIASIS
Trichonympha or Lopomonas causesLEUCORRHOEA (Burning sensation and frothy discharge from vagina)