KINGDOM - PROTISTA

All the organisms included in Protista are unicellular (acellular) eukaryotes. Members of Protista are primarily aquatic. This kingdom forms a link with the others dealing with plants, animals, and fungi. Boundaries of this kingdom are not well defined.

Living organism included in Protista are as follow :

(1) Dinoflagellates (Pyrrophyta) :

Dinoflagellates are mainly marine. They are found on the surface of the water. They appear yellow, green, brown, blue or red depending on the main pigment present in their cells. The pigment present in them is chlorophyll 'a', chlorophyll 'c' and xanthophylls (Dinoxanthin and Didinoxanthin). In dinoflagellates, nutrition is mainly holophytic (Plant-like nutrition/photosynthesis). They have starch as stored food. Their cell wall is divided into plates, which are made up of cellulose. Therefore the covering of dinoflagellates is seen as armoured so they are called as armoured algae. They have two flagella, one lies longitudinally and the other transversely in a furrow between the wall plates. They show a special type of movement which is like whirling whips, therefore they are called "whirling whips". They are called mesokaryotes due to the absence of histone protein in their chromosomes. They show 'bioluminescence' due to the presence of photogenic granules in the cytoplasm, so that these dinoflagellates are also known as 'night light'. They are also called as "fire algae"  because they appear as glowing light due to bioluminescence. e.g. of dinoflagellates - Ceratium, Gonyaulax, Gymnodinium, Pyrocystis. Gonyaulax spreads on the surface of seawater, through rapid multiplication due to which the seawater appears red. It is called red tide. Gymnodinium and Gonyaulax are toxic dinoflagellates. They secrete toxins. These toxins cause paralysis in human beings. Humans acquire these toxins through the food chain. These algae also affect marine animals (water bloom).

(2) Diatoms (Chrysophyta) :

This group includes diatoms and golden algae (desmids). They are found in freshwater as well as in marine (mainly diatoms) environment. They are found in different shapes such as circular, rectangular, triangular, elongated and boat-shaped. The cell wall of Diatoms is made up of cellulose in which silica particles are embedded in many places. Due to which the cell wall appears to be made up of silica. This silicated cell wall is called "shell" or "frustule". Their cell wall is made up of two halves, which are arranged like the lids of soapbox. Their cell walls have silica in very large quantities. Due to this reason, their cell wall is hard. The cell wall does not get destroyed after their death so, at the bottom of the sea, very huge rocks of dead diatoms are formed which are known as "diatomite" or "diatomaceous earth" or "keiselgurh". Diatoms have pigments are Chlorophyll 'a', chlorophyll 'c' and xanthophyll (fucoxanthin). They are chief producers in the ocean. Their stored foods are Leucosin (Chrysolaminarin) and fats (oil). They are immotile because flagella are absent in them. They float passively on the surface of water due to two low molecular weight of stored fats. In diatoms during reproduction special type of spores are formed which are known as "Auxospore".

Use of diatoms :

1. sound proofing
2. Filteration of oils and syrups 
3. Stone polishing
4. As "Heat insulator" in steam boilers because of the keiselgurh bad conductor of heat.

(3) Euglenoids (Euglenophyta) :

Previously euglenoids were placed in plant kingdom due to their photosynthetic ability. But due to the absence of cell walls and animals like nutrition, some scientists placed them in the animal kingdom. But now according to the five-kingdom classification they are included in Protista. They are found as free-living organisms in freshwater lakes, ponds (stagnant water), etc. But some times they are also found in damp soil and brackish water. Though they are photosynthetic in the presence of sunlight, when deprived of sunlight they behave like heterotrophs by predating on other smaller organisms. They are unicellular, the cell wall is absent around them. They are surrounded by a cell membrane which is made up of lipoprotein and this cell membrane is covered with a pellicle. The pellicle is mainly made up of protein and it is elastic in nature. At the anterior end of Euglenoids, a cavity is present, which is known as a reservoir. The flagellum is originated from the base of reservoir. Euglenoids have only one functional flagellum and one non-functional flagellum. One eyespot is present in the anterior position. They have a contractile vacuole and it helps in osmoregulation they have chlorophyll-containing pigments chlorophyll a, chlorophyll b and xanthophyll (zeaxanthin) which is identical to pigments of higher plants. The stored food of euglenoids are paramylum and fat.

(4) Slime moulds:

These organisms develop a slimy mass at the time of their vegetative phase, therefore they are called slime moulds. They are also called as false fungi. They are saprophytic found on decaying twigs and the leaves, their body moves along decaying twig ingulfing organic material. Under suitable conditions, they form an aggregation which may grow and spread over several feet called plasmodium. During unfavorable condition plasmodium from fruiting bodies, which bear ports at their tip. The spores possess true walls. There are extremely resistant and survive many years even under adverse condition. The spores are dispersed by the air current.

(5) Protozoans:

All protozoans are heterotrophs and live as predators and parasites. They are believed to be a primitive relative of animals. They are four major group of protozoans-amoeboid protozoans (amoeba, entamoeba), flagellated protozoans (Trypanosoma), ciliated protozoans(paramoecium) and sporozoans(plasmodium-malarial parasite).