Question

Defining "life" is a very difficult task, and scientists don’t all agree on a common list of the characteristics of life. Some of the other characteristics that you may discover and are often listed in textbooks include those bulleted below. Many of these traits are not limited to living things. For example, fire uses energy, grows, and can reproduce, but it is not considered alive in part because it cannot evolve; its traits are necessary, but not sufficient, for life. NASA scientist Bruce Jakosky, in his book The Search for Life on Other Planets, provides a generally accepted definition of something being “alive” if it 1) utilizes energy from some source to drive chemical reactions, 2) is capable of reproduction, and 3) can undergo evolution.

All living things (organisms)
• use energy (metabolism)
• maintain a stable internal environment (homeostasis)
• detect and respond to select external stimuli
• show growth and development; that is, specialization of cells or structures. Even unicellular organisms show a tiny amount of growth, and single cells repair and use materials from the environment to replace internal structures as needed.
• reproduce
• have some form of nucleic acid as the hereditary molecule
• show adaptation or change over time
• are made of one or more cells

Are viruses alive? This debate rages among scientists. Here we see the action of a virus as it enters a human cell. Consider the passage detailing the characteristics of life and this illustration. Cite evidence to defend the point of view that viruses are alive.

Answer 1

First seen as poisons, then as life-forms, then biological chemicals, viruses today are thought of as being in a gray area between living and nonliving: they cannot replicate on their own but can do so in truly living cells and can also affect the behavior of their hosts profoundly. The categorization of viruses as nonliving during much of the modern era of biological science has had an unintended consequence: it has led most researchers to ignore viruses in the study of evolution. Finally, however, scientists are beginning to appreciate viruses as fundamental players in the history of life.

Answer 2

The debate on whether viruses are alive remains contentious among scientists. Some argue that viruses meet certain criteria for life, such as utilizing energy, reproducing, and showing adaptation over time, as detailed in NASA scientist Bruce Jakosky's definition. However, others contend that viruses lack key characteristics, such as cellular structure and independent metabolism, making their status as living entities a subject of ongoing scientific discussion.

Step-by-step explanation:

The question of whether viruses are considered alive stems from the complex nature of these entities. Viruses exhibit some characteristics associated with living organisms, such as the ability to use energy, reproduce, and undergo adaptation.

For instance, the illustration of a virus entering a human cell demonstrates its capability to interact with host cells and undergo a reproductive cycle.

The presence of nucleic acid in the form of DNA or RNA further aligns with one of the characteristics of life. However, the absence of independent metabolism and cellular structure raises questions about the status of viruses as living entities.

Bruce Jakosky's definition provides a framework that includes energy utilization, reproduction, and adaptation as criteria for life. Applying this definition to viruses, one could argue that they exhibit these traits, especially when considering their interactions with host cells.

However, the lack of cellular structure and the dependence on host machinery for replication challenge the conventional understanding of life.

The ongoing debate underscores the complexity of defining life and the need for nuanced considerations when applying criteria to entities like viruses that blur the boundaries between living and non-living.