how do you know whether something is living or not?

like someone I think told me that viruses are not really living; but I'm not sure?

http://mimi.essortment.com/characteristics_rbrc.htm

http://en.wikipedia.org/wiki/Virus

Determining whether something is living or not can be done by considering certain characteristics. Let's explore this further:

According to the first source you provided, here are the key characteristics of living things:

1. Cellular organization: Living things are composed of cells, the basic structural units of life.
2. Reproduction: Living things have the ability to reproduce and pass on their genetic information.
3. Metabolism: Living things undergo chemical reactions, such as obtaining and using energy.
4. Growth and development: Living things can grow and develop throughout their life cycle.
5. Response to stimuli: Living things can respond to their environment or external stimuli.
6. Homeostasis: Living things can maintain a stable internal environment.
7. Adaptation: Living things can change and adapt to their environment over time.

Viruses, on the other hand, have certain characteristics that make them different from living organisms. According to the second source you provided, viruses lack some of the essential characteristics of living things. Here's a brief overview:

1. Viruses are not made up of cells, so they lack cellular organization.
2. They cannot reproduce independently. Instead, they can only replicate by infecting a host cell and using the host’s cellular machinery.
3. Viruses do not possess metabolism. They do not carry out chemical reactions for energy production or other functions.
4. Growth and development do not occur in viruses. They do not increase in size or go through stages of development like organisms.
5. Viruses do not respond to stimuli or their environment. They lack the capacity to regulate their internal environment or actively interact with their surroundings.
6. While viruses can adapt to some extent, they do not evolve in the same way as living organisms. Virus evolution is driven by mutation and natural selection.

Based on these facts, it is generally accepted that viruses are not considered living organisms. However, they do possess some characteristics that blur the boundaries between living and non-living entities.

In conclusion, when determining the status of something as living or not, it is important to consider the fundamental characteristics of life and how they align with the nature of the entity in question.