27. Viruses, Bacteria and Fungi

Chapter 27 of our e-book will cover in depth the study of Viruses, Bacteria and Fungi, an essential topic for the ENEM test. These microorganisms, although small, have a significant impact on life on Earth, from maintaining ecological balance to causing various diseases.

Viruses

Viruses are extremely small infectious agents, much smaller than cells, and are made up of a nucleic acid molecule, which can be DNA or RNA, surrounded by a protein coat. They are considered obligate intracellular parasites as they need to invade a host cell to replicate.

Viruses are classified according to the type of nucleic acid they possess, the structure of the capsid and the presence or absence of a lipoprotein envelope. Some examples of illnesses caused by viruses include influenza, AIDS, measles, Ebola, and COVID-19.

Viruses also play an important role in evolution, as they can transfer genes between different species, a process known as horizontal gene transfer.

Bacteria

Bacteria are single-celled organisms that come in a wide variety of shapes, including spheres (cocci), rods (bacilli), and spirals (spirochetes). They have a rigid cell wall, which protects the cell and gives it its shape, and a circular DNA genome.

Bacteria can be found in almost every habitat on Earth, including soil, water, air, and in the human body. They play a crucial role in biogeochemical cycles such as the nitrogen cycle and are also important for human health. For example, bacteria in the human gut aid digestion and produce vitamins.

Some bacteria, however, are pathogenic and cause diseases such as tuberculosis, bubonic plague, syphilis and cholera. Antibiotic resistance is a growing problem with pathogenic bacteria.

Fungi

Fungi are a group of eukaryotes that includes organisms such as yeasts, molds, and mushrooms. They have a cell wall made up of chitin and are heterotrophic, meaning they get their nutrients from other organic sources.

Fungi play a crucial role as decomposers in nature, breaking down dead organic matter and recycling nutrients back into the soil. They also form symbiotic associations with plants, helping to absorb water and nutrients.

Some fungi, however, are pathogenic and can cause disease in plants, animals, and humans. Examples include black bread mold (Aspergillus), which can cause lung infections, and the fungus that causes athlete's foot.

In summary, viruses, bacteria, and fungi are groups of microorganisms with a wide range of functions and impacts on life on Earth. The study of these organisms is fundamental for the understanding of biology and human health, as well as for the preparation for the ENEM test.

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65Protozoa and Invertebrates

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