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.
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.