What are the physical features of the protista kingdom?

Answer 1

Protista have characteristics of both plants and animals. Most protista are unicellular and can only be seen with a microscope, but some are composed of more than one cell. They inhabit many environments-fresh water, seawater, soils, and the intestinal tracts of animals. Many species make their own food by photosynthesis like plants, but can move around under their own power like animals. Some protista are single-celled organisms propelled by numerous tiny, hair-like projections called cilia. Cilia also bring food particles into a small depression in their body surface through which food is ingested. Others move by means of flagella, long whiplike structures that the protists beat to propel themselves through water like spinning propeller. Amoebas and slime molds are protista that use pseudopodia for movement and to engulf prey. All protists have a nucleus, some contain multiple nuclei-up to ten thousand in one cell-and others have two different-sized nuclei in a single cell. The DNA of protists is in chromosomes within the nucleus. Protists reproduce by mitosis. In some protists the thin membrane around the nucleus survives mitosis, whereas in plants, animals, and fungi this nuclear membrane disintegrates.

Answer 2

The most important protozoans range usually from 10 to 52 micrometers, but can grow as large as 1 mm, and are seen easily by microscope.

They were considered formerly to be part of the protista family. Protozoa exist throughout aqueous environments and soil, occupying a range of trophic levels.

Motility and digestion

Tulodens are one of the slow-moving form of protozoans. They move around with whip-like tails called flagella, hair-like structures called cilia, or foot-like structures called pseudopodia. Others do not move at all.

Protozoa may absorb food via their cell membranes, some, e.g., amoebas, surround food and engulf it, and yet others have openings or "mouth pores" into which they sweep food. All protozoa digest their food in stomach-like compartments called vacuoles.

Ecological role

As components of the micro- and meiofauna, protozoa are an important food source for micro invertebrates. Thus, the ecological role of protozoa in the transfer of bacterial and algal production to successive trophic levels is important. As predators, they prey upon unicellular or filamentous algae, bacteria, and micro fungi. Protozoa are both herbivores and consumers in the decomposer link of the food chain. They also control bacteria populations and biomass to some extent. Protozoa such as the malaria parasites (Plasmodium spp.), trypanosomes and leis mania, are also important as parasites and symbionts of multicellular animals.

Life cycle

Some protozoa have life stages alternating between proliferative stages (e.g., trophozoites) and dormant cysts. As cysts, protozoa can survive harsh conditions, such as exposure to extreme temperatures or harmful chemicals, or long periods without access to nutrients, water, or oxygen for a period of time. Being a cyst enables parasitic species to survive outside of a host, and allows their transmission from one host to another. When protozoa are in the form of trophozoites (Greek, tropho = to nourish), they actively feed. The conversion of a trophozoite to cyst form is known as encystation, while the process of transforming back into a trophozoite is known as excystation.

Protozoa can reproduce by binary fission or multiple fission. Some protozoa reproduce sexually, some asexually, while some use a combination, (e.g., Coccidia). An individual protozoon is hermaphroditic.