Protoctista are unicellular eukaryotes. Protozoa, diatoms and unicellular algae are included in it.

They have membrane bound organelles such as nucleus with chromosomes enclosed in nuclear membrane, mitochondria, chloroplast (in photosynthetic protoctists only), golgi bodies and endoplasmic reticulum.

Mitochondria are the respiratory organelles. Protoctists are either photosynthetic, parasitic or saprotrophic.

For locomotion, protoctists may have cilia or flagella having 9 + 2 microtubules unlike those of bacteria, which consist of only one spirally coiled protein, called flagellin.

They reproduce both asexually and sexually.

Classification of Protoctista

The kingdom protoctista includes

Phylum Protozoa which has four classes:

  • (i) Rhizopoda: Example, Amoeba
  • (ii) Flagellata: Example, Euglena
  • (iii) Ciliata: Example, Paramecium
  • (iv) Sporozoa: Example, Plasmodium

The protistan algae belong to

  • 1. Phylum Bacillariophyta: Example, Diatoms
  • 2. Phylum Chlorophyta: Example, Chlorella