Kingdom Protista (Protozoa): General Characters and Major Groups of Protozoa

The Kingdom Protista includes mostly unicellular eukaryotes such as protistan algae, Slimemoulds and Protozoans.

On evolutionary point of view this kingdom acts as as a connecting link between prokaryotic monera and multicellular eukaryotic kingdom.(fungi, plant and  animals)

Examples: Euglena, Paramecium, Gonyaulax,

Diatoms, Amoeba, Entamoeba

General Characters of Protozoa:

• Protoplasmic level of organization ; no organs or tissues.
• Their shape may be constant or variable(Amoeba).

Nutrition: Euglena like protists show a double life; auto trophic and heterotrophic.

Many of the protists are photosynthetic autotrophs found mainly in fresh water and oceans. They are called phytoplankton e.g. diatoms.

• Structure: Mostly unicellular and posses typical cell organelles like nucleus, mitochondria, endoplasmic reticulum (ER), Golgi bodies and plastids.
• Locomotion:  Some of them have cilia or flagella with 9+2 internal microtubular structure.
• Reproduction: Asexual Methods (Binary Fission, Multiple fission, budding and spore formation) and Sexual methods by fusion of gametes.
• Life Cycles: Zygotic Meiosis and Gametic Meiosis

Classification of Protozoa : Major groups of Protista

1. Photosynthetic Protists

• Examples: Dinoflagellates, Diatoms and Euglenoids

2. Slime moulds : 

• Cellular Slime moulds ( Dictyostelium)
•  Acellular Slime moulds (Physarella and Physarum)

3. Protozoan Protists

• Zooflagellates (Trypanosoma, Leishmania, Trichomonas, Trichonympha)
• Amoebae (Amoeba, Entamoeba)
• Sarcodines (Radiolarians and Foraminiferans)
• Ciliates (Paramecium, Opalina, Vorticella)

Learn more: Protozoan diseases |  MCQ on Kingdom Protista