Protozoa vs Protista
Living organisms are classified into five kingdoms, such as Monera, Protista, Fungi, Animalia and Plantae. Kingdom protista is a special kingdom among these. All living eukaryotes, which cannot be included into other kingdoms such as Plantae or Animalia, are grouped altogether into one group called protista.
Kingdom protista includes mostly unicellular organisms. Even multicellular organisms that do not have specialized tissues, for an example algae, are included into protista. Protista may be parasitic or free living organisms. Protista reproduce sexually and asexually and include photoautotrophic and heterotrophic organisms. These are found in different kinds of environmental habitats. Most members of protista have cell walls such as algae and slime moulds except protozoa.
Kingdom Protista is again grouped into three subkingdoms: Protophyta, protozoa and slime moulds. Protophyta are plant like organisms and similar to ancestors of the plant kingdom, which consist of several phyla. Protozoa is similar to ancestors of animals and mainly they are aquatic. Slime moulds are fungus like.
This group consists of unicellular, heterotrophic organisms, which are closely related to animals. These are found in different kinds of environmental habitats. Most of them are free living organisms in the fresh water or marine water, or some are living in the decaying organic matter. Some protozoa are parasitic to animal or plant: for an example Plasmodium, which cause malaria. Protozoa vary in size from micrometers to centimeters in diameter.
Protozoa usually does not have cell walls, but some phyla may be surrounded by a shell. Protozoa has alternative generation between vegetative form (trophozoite) and the resting spore called cyst. Most protozoa cells are multinucleate, but some have single nucleus. They have contractile vacuoles, which remove excess water. They have a special kind of motion using three types of locomotors such as flagella, cilia, and pseudopodia. Flagella and cilia have a similar structure to (9+2) system of microtubules. This characteristic is unique to protozoa.
Protozoa are divided into four phyla: Flagellates (or Mastigophora), Amoeboids (or Sarcodina), Sporozoans (or Sporozoa, Apicomplexa) and, ciliates (or Ciliophora). This classification is based on the locomotion and not phylogenetic.
What is the difference between Protista and Protozoa?
• Protozoa is a subkingdom of the protista.
• Protista Kingdom includes plant like Phytotrophs, animal like prtotozoa, and fungus like slime moulds, whereas protozoa only has animal like unicellular or multicellular organism.
• Protista consists of heterotrophic and autotrophic organisms whereas most protozoa are heterotrophs.
• Some Protista are autotrophic organisms, so they synthesize their own foods, whereas protista contains only hetrotrophs. So they ingest their foods through the membrane.
• Most of the protista have cell walls such as in algae and slime moulds, whereas protozoa do not have cell walls.
• Protozoa has a special type of motion using three types of locomotors such as flagella, cilia, and pseudopodia, whereas most protista cannot move.
• Motility is essential for the survival of protozoa, whereas all protista does not need motility for their survival.
• Some of the protista have different steps in their life cycle from sexual to asexual as example algae, whereas protozoa have vegetative form, which is called trophozoite and dormant form called cyst.