Why are protozoa the most primitive and lowest animals?

This is due to the fact that protozoa have the fewest genetic cells and the least developed ones, so they are called the lowest animals.

Protozoa are one of the simplest organisms. Although they make up a sub-world, they are not necessarily related to each other. From a biological point of view, they do not belong to a natural group, but to a large number of biological systems.

Because they have only one cell to form a complete living body, various physiological functions, such as movement, induction, digestion, respiration, excretion, reproduction and other life phenomena are completed in one cell.

Because protozoa are unicellular animals, and the subclass phytoflagella in protozoa can be autotrophic, and compared with the generally understood multicellular animals, it is the most primitive and low-level and simple; Protozoa is both a cell and an individual, and as a cell, its cytoplasm can be differentiated into various organelles to carry out various physiological functions, so the cell structure and function are more complex than ordinary cells.

Both. Plants and animals have them.

Early Paleozoic. About 100 million years ago 100 million years ago, including the Cambrian of the Paleozoic Era and the Ordovician.

and Silurian 3 era.

During this geological epoch, there were large algae blooms in the oceans before the Cambrian, and the species and number of plants were already very large. At the same time, many lower animals are active among the seaweed. After entering the Cambrian period, there was a widespread transgression on the earth, and the area of the ocean was further expanded, creating conditions for the growth of marine life, some primitive invertebrates.

It gradually evolved into invertebrates with a hard shell.

Therefore, due to the emergence of a large number of biological varieties in the Cambrian, there is a term in academic circles called "Cambrian explosion of life". It is the mushrooming appearance of different phyla of invertebrates with hard shells, including arthropods.

Molluscs, brachiopods, ancient cups, pen stones, tooth-shaped spines, etc. Their rapid emergence has formed a spectacular situation of biological giants, bringing about a major leap in the evolutionary process of organisms from shellless to shelled.

Historical archaeology proves that in the early Paleozoic, lower plants, such as single-celled lower plants, appeared first, and then animals appeared.

Protozoa belong to the phylum Protozoa, which are the most primitive, simplest, and lowest animals.

Their main feature is that the body is made up of single cells, all of which are single-celled animals.

Protozoa are single-celled organisms with specialized organelles in their cells, which have all the functions necessary to sustain life and continue to progeny, such as mobility, nutrition, respiration, excretion, and reproduction.

Every protozoa is a complete organism.

Common protozoa include: Euglena, amoeba, paramecium, malaria parasite, ciliate, flagellates, strawworms, Giardia lambli, etc.

Partial protozoa.

Protozoa are a class of protists that are closer to animals, referred to as protozoa. Composed of single cells, heterotrophic and motil. But there are species that fall somewhere between plants and animals, such as euglena because they are capable of photosynthesis; They are also able to move and eat like real animals.

Protozoa are excluded from the animals, and the remaining multicellular animals are called metazoans. Metazoans that have tissue differentiation are called true metazoans.

The main characteristic of the phylum Protozoa is that the body is made up of a single cell, hence the name unicellular animal. Although they are complex in morphological structure, they are only a differentiation of the cell itself.

Although there are groups among them, each individual cell in the group generally lives independently and is not closely related to each other, so they are low-level, primitive animals in terms of development. In addition to single-celled individuals, protozoa also have groups formed by the aggregation of several or more individuals, much like multicellular animals, but it is different from multicellular animals, mainly due to the difference in the degree of cell differentiation. The cells in the body of multicellular animals generally differentiate into tissues, or further form organs and systems, coordinate activities to become a unified whole, and the individual who makes up the group, the cells generally do not differentiate, at most only the differentiation of somatic cells and germ cells.

Somatic cells do not differentiate, and individuals within the population are relatively independent.

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