How life defined?

How you determine whether something is alive or not? Life and living beings are defined by seven characteristics that differentiate them from everything that has life. Living beings meet all seven characteristics of life.

A living being consists of one or more cells working in an orderly fashion. The cell itself is composed of individual parts that work in coordination. Several cells can organize to form tissues, a set of tissues that performs a specific function is a body, the organs can form organ systems, etc. This structuring least complex known as hierarchical levels of organization. The tendency to self-organization is an important feature of life.

Living things need energy to grow, reproduce and maintain their complexity against the forces of entropy. For this transform chemicals and organic materials by a process of synthesis or degradation.

Living things need to resist the forces of entropy (the natural tendency toward disorganization). To maintain the constancy of the internal environment of your body (body temperature, electrolyte balance, etc.) need to expend energy.

All living things grow at some point. Growth depends on the ability to metabolize, or change external material energy. Living things grow structured manner described in number one (complexity and organization).

All living beings have the ability to reproduce in any way. Reproduction may be sexual or asexual. Asexual reproduction is usually done in simpler organisms and is an extension of the growth process. For example, bacteria grow to a certain point and then divided, producing an exact copy of the original bacteria. Sexual reproduction usually requires two individuals who combine their genetic material to create a third individual with different features.

A living detects and reacts to stimuli such as light, pressure, temperature and / or composition of the soil, air, water, etc. This reaction is active (requires energy), not passive. For example, the reaction of a plant to sunlight is different than a stone rolling down. The plant produces energy to grow toward the sun (an active reaction), while the stone does not produce requires energy to roll, but moves by physical force of gravity.

Living things change over generations; this happens on the scale of a population, not an individual. The evolution allows the adaptation of populations to their environment. The Theory of Evolution is a scientific theory, not a common theory. A scientific theory is an explanation of a phenomenon that is supported by scientific observations. In science there is always the possibility of changing our understanding of our environment with future observations and technologies that do not yet exist, so it is called a theory. However, common words, a scientific theory is a fact: it is something that has been proven with current technologies and is accepted by the scientific community.