28. Protozoa and Invertebrates

Chapter 28 of our Biology course for ENEM addresses two important topics: Protozoa and Invertebrates. These two groups of organisms are frequently required in ENEM tests, and a clear understanding of their characteristics and importance is essential for good performance.

Protozoa

Protozoa are unicellular and heterotrophic organisms, classified in the Kingdom Protista. They can be found in a variety of environments, from fresh and salt water to soil and in the bodies of other organisms such as parasites. Protozoa are divided into four main groups: amoebae, flagellates, ciliates, and sporozoans.

Amoebas are characterized by their variable shape and locomotion by pseudopods, extensions of the cytoplasm that allow movement and capture of food. Some examples of amoebas include Amoeba proteus, found in fresh water, and Entamoeba histolytica, a human parasite that causes amoebiasis.

Flagellates have one or more flagella, long, thin structures that enable locomotion. Some flagellates are parasites, such as Trypanosoma cruzi, which causes Chagas disease, and Trypanosoma brucei, which causes sleeping sickness.

Ciliates have cilia, small projections that allow locomotion and feeding. An example of a ciliate is Paramecium, commonly found in fresh water.

Sporozoans lack structures for locomotion and are all parasites. An example is Plasmodium, which causes malaria.

Invertebrates

Invertebrates are a diverse group of animals that lack a backbone. They represent the vast majority of animal species and include groups such as porifera, cnidarians, flatworms, nematodes, molluscs, annelids, arthropods and echinoderms.

Porifera, or sponges, are sessis (do not move) animals that live in aquatic environments. They have a porous body, through which water is constantly filtered for food.

Cnidarians include animals such as jellyfish, corals, and sea anemones. They have specialized cells called cnidocytes, which are used for food capture and defense.

Platyhelminthes are flatworms that can be free or parasitic. Examples include flatworms, which live in aquatic environments, and Schistosoma, a human parasite that causes schistosomiasis.

Nematodes are cylindrical worms that can be free or parasitic. Examples include Caenorhabditis elegans, a model organism in biological research, and Ascaris lumbricoides, a human parasite that causes ascariasis.

Molluscs are a diverse group that includes animals such as snails, slugs, oysters, mussels, and squid. They have a soft body, usually protected by a shell.

Annelids are segmented worms that include earthworms and leeches. They are important decomposers in the soil, contributing to the recycling of nutrients.

Arthropods are the largest group of animals and include insects, arachnids, crustaceans, and myriapods. They have a chitinous exoskeleton and jointed appendages.

Echinoderms are marine animals that include starfish, sea urchins, and sea cucumbers. They have a calcareous endoskeleton and a system of water channels used for locomotion and feeding.

In summary, protozoa and invertebrates are groups of organisms with an incredible diversity of shapes, sizes, and ways of life. They play important roles in ecosystems and, in some cases, human health. Understanding its characteristics and importance is essential for a complete understanding of biology and for a good performance in the ENEM.

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