Question

Virus is (a) Completely non-living (b) Inert crystalline structure outside the living cell (c) Cellular organism (d) One of Whittaker's classification

Short answer

(b) Inert crystalline structure outside the living cell

Step-by-step solution

Understanding Viruses

Viruses are unique biological entities because they display both living and non-living characteristics. They aren't composed of cells, they aren't able to perform any metabolic function on their own, and can't reproduce independently. Their existence is entirely contingent upon the cells they infect.

Examining the Answer Choices

(a) Completely non-living: This option is incorrect, viruses exhibit some characteristics of life, such as the ability to reproduce, but only within a host cell.\n(b) Inert crystalline structure outside the living cell: This option is correct. Outside of a host cell, viruses exist as a dormant particle, or virion. These particles can form crystalline structures when subjected to certain conditions.\n(c) Cellular organism: This option is incorrect, viruses aren't considered cellular organisms as they aren't composed of cells.\n(d) One of Whittaker's classification: This option is incorrect. Whittaker's five-kingdom classification does not include viruses. It divided organisms into five kingdoms - Monera, Protista, Fungi, Plantae, and Animalia based on characteristics such as complexity of cell structure.

Selecting the Correct Answer

Based on the information from Steps 1 & 2, the correct answer is (b) Inert crystalline structure outside the living cell.

Key concepts

Viruses

Viruses are fascinating entities, straddling the line between living and non-living. When outside a living host, they remain dormant. This form is often described as an inert crystalline structure. Although they don't perform metabolic activities like cellular organisms, they can become active when they enter a host.

Here, they hijack the host's cellular machinery to reproduce. Notably, viruses are not composed of cells themselves. Their structure is rather simple compared to cellular organisms. Viruses consist primarily of genetic material (DNA or RNA) enclosed in a protein coat.

Despite showing some characteristics of living organisms once inside a host, they lack some critical life features such as growth and self-repair without a host. These nuanced characteristics make viruses a unique study subject in biology.

Whittaker's classification

Whittaker's classification was a groundbreaking system developed in the late 1960s for dividing life forms into five distinct kingdoms. These kingdoms are Monera, Protista, Fungi, Plantae, and Animalia. The criteria for classification were based on characteristics such as cell structure, cellularity, mode of nutrition, and reproduction.

Importantly, viruses do not fit into any of these kingdoms. Since they are not cellular organisms, Whittaker's system didn't include them. This classification generally deals with organisms that have clear cellular organization, unlike viruses, which depend on other organisms' cells to function.

By focusing on more traditional structures of life, Whittaker's classification highlights the diversity and complexity within living kingdoms but also leaves a gap that underscores the unique nature of viruses in the biological world.

Cellular Organisms

Cellular organisms differ fundamentally from viruses. They are defined by a singular characteristic: being composed of one or more cells. This cellular structure is the basis of life forms as we understand them.

Cellular organisms fall into two categories based on their complexity. Prokaryotic cells are simpler and do not have a nucleus, like bacteria. Eukaryotic cells, on the other hand, have a nucleus and are more complex, as seen in plants, animals, fungi, and protists.

Unlike cellular organisms, viruses lack any cellular organization. They do not have cell membranes, organelles, or the cellular machinery for energy production or reproduction. While cellular organisms grow and reproduce independently, viruses require a host cell to replicate. These differences are crucial in understanding why viruses are considered distinct from traditional forms of life.