Science

Kingdom Protista – Plant like Protists & its Characterstics

Kingdom Protista – Plant like Protists

 In Five Kingdom Classification by R.H. Whittaker, Algae is included in three kingdom i.e. Kingdom Monera, Kingdom Protista, Kingdom Plante. Three group of Algae like Protists i.e. Chrysophytes, Dinoflagellates and Euglenoids are included in Kingdom Protista.

    Plant like Protists or Algae like Protists are chlorophyll bearing Photosynthetic Protists of Kingdom Protista.

    Autotrophic in Nutrition – use light energy to make their own food.

    These are mostly Planktonic i.e. occurs near water surface.

    About 50 to 60% of Earths oxygen is released by plant-like protists.

    Many organisms rely on plant-like protists for food.

    Many plant-like protists are flagellates, called phytoflagellates – (phyto- means plant).

Classification of Plant like Protists

    They have been classified in 3 main groups –

1.    Chrysophytes

2.    Dinoflagellates

3.    Euglenoids

Chrysophytes

    This group includes diatoms and golden algae (desmids) and Yellow green Algae.

    They are found in fresh water as well as in marine environments.

    Chrysophytes are microscopic and float passively in water currents (plankton).

    Characteristic Pigment of this group is Chlorophyll a and c and Fucoxanthin, Carotenoid.

    They store their food in the form of Fats, oils and unique polysaccharide called Laminarin.

Diatoms

    Dominant member of group.

    Mostly unicellular but some forms colonies. The cell is of Variable shapes.

    The cell wall is formed of two thin overlapping shells, which fit together as in a soap box.

    The two part overlapping cell wall is called Frustule. The upper half is called Epitheca and lower half is called Hypotheca.

    The walls are embedded with silica due to which they are indestructible. Thus, diatoms have left behind large amount of cell wall deposits in their habitat. This accumulation over years is known as ‘diatomaceous earth’.

    Being gritty this soil is used in polishing, filtration of oils and syrups. Being heat resistant, it is also used in insulators of boilers and blast furnace. Also used in manufacture of switches and fuse boxes with Bakelite.

Dinoflagellates

    Also known as Pyrrhophyta (“fire algae”; Greek pyrrhos, fire).

    These organisms are unicellular, mostly marine and photosynthetic.

    The chief pigments are Chlorophyll a and c and variety of Carotenoids. They appear yellow, green, brown, blue or red depending on the main pigments present in their cells.

  The Cellulosic cell wall has stiff plates on the outer surface which gives them armoured appearance.

   Most of them usually have two flagella which lies longitudinally and transversely in a grooves between the wall plates.

 Known as Dinoflagellates due to spinning caused by activity of transverse flagellum and longitudinal flagellum represent Spinning whips.

    Starch is the main food reserve.

    They have single layer nuclear membrane (double layered in all other Eukaryotes).

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

    Dinoflagellates reproduce asexually through cell division or by the formation of zoospores and cysts.

   Red Tides – population explosions (“blooms”) that can color the water with pigmented dinoflagellate cells; red tides kill marine life due to the high concentration of toxins from the dinoflagellates. E.g. Gonyaulax, Gymnodinium etc.

 Zooxanthellae – symbionts (live in mutually beneficial relationship) in other organisms (jellyfish, sea anemones, mollusks, corals) zooxanthellae in corals do photosynthesis and make carbon products absorbed by coral.

 Bioluminescent – many planktonic dinoflagellates emit light when disturbed which creates sparkling waves. It is due to light producing protein luciferin are called fire algae. E.g. Noctiluca, Pyrocystis, Pyrodinium etc.

Euglenoids

    Euglenoids are free living, found in Freshwater Pond and ditches or damp soil.

 They are Heterotrophic.  Some are facultative heterotrophs, photosynthetic forms that can switch to being heterotrophs if kept in the dark, and switch back to autotrophs if given enough light.

    Some form are photosynthetic (using chlorophylls a and b, like green algae and plants).

    Instead of a cell wall, they have a protein rich layer called Pellicle which makes their body flexible.

The Pellicle encloses cytoplasm which is divisible into two zonesEctoplasm (dense clear peripheral zone) and Endoplasm (Fluid like granular central zone). Endoplasm contains various cell organelles.

 Two flagella are present, one is long and other is short. The two flagella join with each other at a swelling called paraflagellar body.

    Attached to the membrane of reservoir at the level of paraflagellar body, an orange-red coloured eye-spot or stigma which act as a Photoreceptor.

    Only asexual reproduction by Binary fission.

So, this was all about the Kingdom Protista –Plant like Protists and their Characteristics. In the next post (Click here), we will discuss about the Fungi like Protists in detail.

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