Kingdoms - SS1 Biology Lesson Note

Whilst Carolus Linnaeus divided life into just the plant and animal kingdom, modern biology recognizes the existence of five distinct kingdoms for classifying life on Earth:

1. Monera

Protista

Fungi

Plantae

Animalia

In the classification, however, viruses do not fit into any of the kingdoms.

A virus is a microscopic infectious agent that can only replicate inside the cells of living organisms. It is a non-living particle composed of genetic material, either DNA or RNA, enclosed in a protein coat called a capsid. Some viruses may also have an outer envelope made up of lipids.

Viruses are considered obligate intracellular parasites because they require a host cell to reproduce and carry out their life cycle. They cannot carry out essential metabolic processes on their own and lack the machinery necessary for replication. Instead, viruses invade host cells and hijack their cellular machinery to replicate and produce more viruses.

When a virus infects a host cell, it injects its genetic material into the cell. The viral genetic material then takes control of the host cell's machinery, forcing it to produce viral proteins and replicate the viral genome. The newly formed viral components assemble to form complete viruses, which can then infect other cells and continue the cycle of infection.

image from lecturio.com

Viruses can infect a wide range of organisms, including animals, plants, and microorganisms. They are responsible for various infectious diseases, such as the common cold, influenza, measles, HIV/AIDS, Ebola, and COVID-19. However, it is important to note that not all viruses cause diseases, as some have more benign or even beneficial effects.

Due to their unique nature, viruses are distinct from other forms of life. They lack the ability to grow, respire, or carry out metabolic functions outside of a host cell. Viruses are often classified based on their genetic material, shape, replication strategy, and the type of host they infect.