Here we discuss about economic importance of phylum protozoa. We also discuss charactristics of phylum protozoa. 

protozoa (Animal like protists) 

                                                    Protozoa is a greakword.pro(first)zoa(animal)so means before animals.  Here we disscuss briefly. 

Evolutionary prospectus :

Ancient members of the Archaea were the first living organisms on this planet.
The Archaea gave rise to the kingdom Protista (also called Protoctista) about 1.5 billion years ago. 
The endosymbiont hypothesis is one of a number of explanations of how
this could have occurred. Most scientists agree that the protists probably arose from
more than one ancestral Archaean group. Depending on the classification system, zo-
ologists recognize between 7 and 45 phyla of protists.
 These phyla represent numer-ous evolutionary lineages. Groups of organisms believed to have had separate origins are said to be polyphyletic (Gr. polys, many  phylon, race). 
Some protists are plantlike because they are primarily autotrophic (they produce their own food). Others are animal-like because they are primarily heterotrophic (they feed on other organisms).

Life within a single plasma membrane :

Protozoa (Gr. proto, first  zoa, animal) display unicellular (cytoplasmic) organization, which does not necessarily imply that they are simple organisms. 
Often, they are more complex than any par-ticular cell in higher organisms. In some protozoan phyla, individuals group to form colonies, associations of individuals that are
not dependent on one another for most functions.
 Protozoan colonies, however, can become complex, with some individuals
becoming so specialized that differentiating between a colony and a multicellular organism becomes difficult.

Reproduction :

Both asexual and sexual reproduction occur among the protozoa.One of the simplest and most common forms of asexual reproduction is binary fission. In binary fission, mitosis produces two nuclei that are distributed into two similar-sized individuals when the cytoplasm divides. 
            During cytokinesis, some organelles duplicate to ensure that each new protozoan has the needed organelles to continue life. Depending on the group of protozoa, cytokinesis may be longitudinal or transverse.



Maintaining homeostasis :

A regular arrangement of microtubules, called the pellicle,underlies the plasma membrane of many protozoa. The pellicle is rigid enough to maintain the shape of the protozoan, but it is also flexible.
The cytoplasm of a protozoan is differentiated into two regions. The portion of the cytoplasm just beneath the pellicle is called ectoplasm (Gr. ectos, outside  plasma, to form). It is relatively clear and firm. The inner cytoplasm, called endoplasm (Grendon, within), is usually granular and more fluid. The conversion of cytoplasm between these two states is important in one kind of protozoan locomotion.

Symbiotic lifestyle :

Many protozoa have symbiotic lifestyles. Symbiosis (Gr. syn, with bios, life) is an intimate association between two organisms. For many protozoa, these interactions involve a form of symbiosis called parasitism, in which one organism lives in or on a second organism, called a host. The host is harmed but usually survives, at least long enough for the parasite to complete one or more life cycles.
The relationships between a parasite and its host(s) are often complex. Some parasites have life histories involving multiple
hosts. The definitive host harbors the sexual stages of the parasite.The sexual stages may produce offspring that enter another host, called an intermediate host, where they reproduce asexually.
Some life cycles require more than one intermediate host and more than one immature stage. For the life cycle to be complete, the final, asexual stage must have access to a definitive host. Other kinds of symbiosis involve relationships that do not harm the host. Commensalism is symbiotic relationship in which one member of the relationship benefits, and the second member is neither benefited nor harmed. Mutualism is a symbiotic relationship in which both species benefit.

So this is all about explain of protozoa.