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Kingdom - Protista

Updated on October 10, 2015

It includes unicellular, eukaryotic, microscopic organisms belonging to plants and animals. The cells have distinct nucleus. Mostly they are aquatic.
This kingdom was created by Haeckel in his 3 - kingdom classification. The protistans may have cell wall or naked. They may be photosynthetic or heterotrophic like fungi and animals. The cells have membrane bound organelles. They show Mitosis and Meiosis in their life cycle.
Protista consists the following groups
1. Chrysophytes
2. Dinoflagellates
3. Euglenoids
4. Slim Moulds
5. Protozoans


1. Chrysophytes:

This includes yellow green algae (e.g.: Vaucheria), yellow golden algae (Desmids) and Diatoms. They live in fresh water or marine water. They float on water and form phytoplankton.

These are unicellular, eukaryotic, microscopic, photosynthetic, aquatic marine and chief producers of the oceans. These are also called pastures of the sea.
The cells are called Frustules.
The cell wall has 2 parts. Upper epitheca and lower hypotheca like a soap box.
Cell wall is made of cellulose and silica due to which cell wall is indestructible. Cells after death form sedimentation beds and form fossils. These fossil masses are called as Diatomaceous earth or Diatomite or Kieselguhr.
Cell walls show various kinds of ornamentation due to which diatoms are called jewels of the sea. They store food in the form of oil. Kieselguhr is gritty due to the presence of silica. So it is used in paints, nail polish, toothpaste, shoe polish, water and oil filters. It gives sparkling appearance.
Basing on symmetry there are 2 kinds of diatoms.
1. Pennales - Bilaterally symmetrical.
Example: Bacillaria
2. Centrales - Radially symmetrical
Example: Coscinodiseus Flagella are absent.

The cells are diploid. They show binary fission during vegetative, reproduction cell division occurs in the night. Sexual reproduction occurs by fusion between gametes. Zygote is formed that becomes Auxospore. It maintains the size of the cells. So it is also called rejuvenatory spores.


2. Dinoflagellates:

These are unicellular, uninucleate, eukaryotic, microscopic, biflagellated, algal protistans.
They are aquatic, marine & photosynthetic.
They have yellow, green, brown, blue or red pigments.
Of the 2 flagella, one is longitudinal anterior and the other is inserted in the groove horizontally. They show 9+2 structures.
They show spinning movements. So they are also whirling whips. The word Dinoflagellates is taken from Latin which means 'whirling swimmers'.
Cell will is stiff with cellulose plates.
Nucleus encloses permanently condensed chromosomes consisting DNA only. Histones are absent. So the nucleus is called Mesokaryon.

Noctiluca (marine) shows bioluminescence. It emits bright, blue green light when disturbed.
Gonyaulax makes the sea red coloured and causes red tides in Mediterranean sea.
The red tides kill the firlees as gonyaulax produces toxins.


3. Euglenoids:

These are unicellular, uninucleate, eukaryotic, microscopic, aquatic, fresh water motile protistans. They live in stagnant water. They show plant and animal characters. They form link between plants and animals.
Cell wall is absent. Pellicle made of protein is present around protoplasm. It is flexible.
A pain of unequal flagella are present anteriorly. The invagination in the anterior side has mouth (cytostome) gullet (cytopharynx) and reservior one below the other. Nucleus is present in the centre. Chloroplasts (Chromato phores) show pyrenoids. The pigments are similar to those of higher plants.
Eye spot or stigma is present on the reservoir membrane. It is photosensitive and helps to move near to light. They are photosynthetic (in light) and heterotrophic (in the absence of light).
Sexual reproduction is absent. Vegetative reproduction occurs by longitudinal binary fission.

Plant characters
1. Presence of photosynthetic pigments.
2. Presence of pyrenoids.
Animal characters
1. Cell wall is absent.
2. Presence of eye spot.


4. Slim Moulds:

It is a group of protists.

  • These are unicellular, eukaryotic, multi nucleate and naked.
    Cell wall is absent (A cellular)
    It looks like moving mass of slime.
    These are saprophytic in nature. They feed on decaying leaves and twigs. They feed on bacteria, yeast and organic matter. They grow up to several feet and form Plasmodium when conditions are favourable.
    When conditions are unfavourable, Plasmodium stops moving and forms fruiting body enclosing spores. These are highly resist and viable for several years.
    Example: Physarum.


5. Protozoans:

These are unicellular, eukaryotic, microscopic first animals. The term protozoa was coined by Goldfuss. They may be free living or parasitic.
There are 4 groups in it
1. Amoeboid Protozoans: They have neither flagella nor Cilia but bear pseudopodia for locomotion. They are unicellular, uninucleate, naked, irregularly shaped. They may be free living (Amoeba) or parasitic (Entamoeba). They show simple fission.
2. Flagellated Protozoans: These are unicellular, uninucleate, eukaryotic, microscopic with flagella as locomotory organs. They are free living or parasitic (Trypanosoma). This parasite causes sleeping sickness disease in Man. It shows longitudinal binary fission.
3. Ciliated Protozoans: These are unicellular, binucleate, eukaryotic, microscopic with cilia as locomotory organs. It shows nuclear dimorphism.
Example: Paramecium (Slipper animalcule).
Cilia also help in taking the food into its gullet. It shows transverse binary fission and conjugation.
4. Sporozoans: They include infections spore producing protists of diverse nature.
Example: Plasmodium Vivax. It causes Malaria.

Differences between Flagella and Cilia:

1. These are definite in number.
1. These are numerous in number.
2. These are definite in position.
2. They may be present anywhere.
3. These are long.
3. These are short.


It is a colonial, temporary, non motile a sexual stage in the life cycle of a motile algal plant or euglenoids.

Kingdom Protista and Kingdom Fungi


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