What are protozoa?

The animals that are unicellular without any tissue grade of organisation but multiply asexually by binary or multiple fissions or by budding, in some cases sexual reproduction by conjugation are regarded as the protozoan. The word protozoa have been derived from the two Greek words, protos which means the first and zoon which means the animal. The protozoa are the first group of organised but simplest animals in animal kingdom. Nearly 30,000 species of unicellular microscopic animals have been included in this phylum. Protozoa are the first group of animals that appearnon this earth surface.

Characteristic of Protozoa: -

i) The protozoa are simple and most primitive animals that are included under the phylum.
ii) Protozoa are very minute and microscopic animals, that is , protozoan cannot be observed only through naked eye, but it may be seen with the help of microscope. However foraminifferan protozoan like Globigerina, Elpidium etc are shelled protozoa and are also microscopic.
iii) Protozoa are unicellular animal, that is, their body is made up of single cell. In the cell body there is a single nucleus though some protozoa posses more than one nucleus. They contain other cell organelles. So, there is no development of tissue or organ system. They maintain their all physiological processes only with the help of single cell.
protozoaiv) Protozoa are solitary. Though in some cases they form colony but the individuals of a colony are similar and independent.
v) The protozoa are off various shapes. Some of them are oval or round, some are cylindrical or disc-like, and also may be of irregular shaped.
vi) In general the protozoan possesses definite locomotory organs. Though in some species, move meant and locomotion is affected by the contraction and relaxation of the protoplasm instead of a definite locomotory organ.
Vii) In some of the Protozoa, cysts are formed during extreme condition.
viii) There are free livings, parasitic or symbiotic natures of animals are present in protozoa.
ix) The protozoan takes oxygen from the surroundings by diffusion process and eliminates carbon dioxide which is produced as a byproduct of their metabolism.
x) Nutrition in protozoan generically takes place by holozoic process. In some cases saprozoic or holophytic mode of nutrition may also occur.
xi) The organelle Contractile Vacuole is present in many protozoa which helps in the excretion of dissolved wastes, specially the excess of water of the body and so it is known as osmoregulatory organ.
xii) In majority of the protozoa, asexual reproduction takes place by binary or multiple fission even by budding process. In some cases sexual production take place by conjugation process.

What is the importance of Protozoa?

The man and the protozoa have some close relationship. Though some of the protozoa are quite harmful for man yet some are beneficial to man, which are as follow: –
i) Some concepts about the protozoa are essential in fish culture. Aquatic insect larvae and small crustaceans use the protozoa as their food material; again the fishes consume the aquatic insect larvae and small crustaceans as their food material. Thus the protozoa are playing a vital role in the food chain.
ii) During exploration of oil in the geological layer, the existence of protozoan fossil shell is helping to find out the oil field.
iii) Many protozoa are used in the laboratory as an experimental material.
iv) Some protozoa create diseases to man, domestic animals, fishes and insects. These are regarded as harmful protozoan.