What is Kingdom Protista ?

All singled celled eukaryotes are placed under protista, bit the boundaries af this kingdom are not well defined what may be a photosynthetic protistan to on biologist May be a plant to another. In this we include chrysophytes , Dinoflagellates , Euglenoids, slime moulds and protozoa under protista. Member of protista are primarily aquatic. This kingdom forms a link with the others dealing with plants, animals and fungi, Being eukaryotes the protistan cell body contains a well defined nucleus and other membrane bound organelles .Some have sexually and asexually by a process involving cell fusion and zygote formation.

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Pro­tista

Chrys­o­phytes:

This group includes diatoms and gold­en algae(desmids) . They are found in fresh water as well as in marine environments . 

They are micro­scop­ic and float pas­sive­ly in water con­tain (plank­ton). Most of them are photosynthetic.

In diatoms the cell worms two thin over­lap­ping shells which fit togeth­er as in a soap box . The walls are embed­ded with sil­i­ca and thus the walls are inde­struc­tible. That’s why diatoms have left behind large amount of cell wall deposit in their habi­tat ; this accu­mu­la­tion over bil­lions of years is ref­ered as ‘diatoma­ceous earth’.

This soil is used in pol­ish­ing , fil­tra­tion of oils and syrups . Diatoms are the chif pro­duc­ers in the ocean.

Dinofla­gel­lates :

These organ­isms are most­ly marine and pho­to­syn­thet­ic. They appear yel­low, green , brown, blue or red depend­ing on the main pig­ments present in their cells ..

The cells has stiff cel­lu­lose plates on the out­er surface . 

Most of them have two fla­gel­la ; one lies lon­gi­tu­di­nal­ly and the oth­er trans­verse­ly in a fur­row between the wall plates .

very often red Dinofla­gel­lates ex ; Gonyaulaux under­go such rapid mul­ti­pli­ca­tion that they make the sea appear red (red tides)

Tox­in released by such large num­bers may even oth­er marine ani­mals such as fishes. 

Eug­le­noids

Most­ly found in stag­nant water . they have a pro­tein rich lay­er called pel­li­cle which makes their body flexible .

They have two fla­gel­la a short and a large one. 

They are pho­to­syn­thet­ic in pres­ence of sun­light and in absence of sun­light they behave as het­erotrophs by pre dat­ing on oth­er small­er organisms.

The pig­men­sts of Eug­le­noids are iden­ti­cal to those present in high­er plants.

eg. Eugle­na

Slime moulds :

Slime moulds are sapro­phyt­ic protista. 

Teh body moves along decay­ing twigs and leaves engulf­ing organ­ic material.

Under. Suit­able con­di­tions they form an aggre­ga­tion called plas­mod­i­um which may grow and spread over sev­er­al feet .

Dur­ing unfa­vor­able con­di­tions the plas­mod­i­um dif­fer­en­ti­ates and forms fruit­ing bod­ies bear­ing spores at their tips.

The spores poss­es true wall. They are extreme­ly resis­tant and sur­vive for many years even under adverse conditions.

Pro­to­zoans :

All pro­to­zoans are het­erotrophs and live as preda­tors or par­a­sites. They are believed to be prim­i­tive rel­a­tives of animals.

They are four major groups of protozoans.

Amoe­boid protozoans :

These organ­isms live in fresh water , sea water or moist soil. They move and cap­ture their prey by putting out pseudopo­dia (false feet) as in Amoeba

eg Enta­moe­ba

Fla­gel­lat­ed Protozoans :

The mem­bers of this group are either free liv­ing or parasitic .

they have fla­gel­la the par­a­sitic forms cause dis­ease such as sleep­ing sickness .

ex Try­panoso­ma

Cil­i­at­ed Protozoans

These are aquat­ic , active­ly mov­ing organ­isms because of the pres­ence of thou­sand of cilia.

They have a cav­i­ty (gul­let) that opens to the out­side of the cell surface . 

The coor­di­nat­ed move­ment of rows of cil­ia caus­es the water laden with food to be steered into gullet 

ex : Paramoecim

Sporo­zoans :

This includes diverse organ­ism that have an infec­tious spore like stage in their life cycle. 

The most noto­ri­ous is plas­mod­i­um (malar­i­al par­a­site) which caus­es malar­ia , a dis­ease which has a stag­ger­ing effect on human population.

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