What is life or the difference between life and non-life? To many people this seems like a silly question because in our daily lives we are perfectly capable of distinguishing their differences and not confusing them. But this is not a simple question. In a nutshell, life should have these characteristics.
1. Cells are the basic unit of living things
The cell is the basic unit that makes up an organism. Bacteria and protists consist of a single cell, and they are called unicellular organisms. Plants and animals are made up of multiple cells, and they are called multicellular organisms. Cells coordinate and cooperate with each other to perform the various life activities.
Metabolism is divided into the synthesis and decomposition of organic compound. Synthesis: the nutrients are ingested from environment and converted into the organics that compose organism. Decomposition is the breakdown of substances in the organism to obtain the energy needed for life activities. When synthesis is greater than decomposition, the organism exhibits growth. When synthesis is less than decomposition, the organism shows wasting.
3. Can respond to stimuli
Organisms respond to various stimuli, such as light, temperature, sound, chemicals, etc. Light: Plants grow toward light sources. Temperature: The vitality of cold-blooded animals depends on temperature. If the temperature is too low, their vitality will decrease or they may even hibernate. To raise their body temperature, some lizards will basking the warm sunshine on the rock. Sound: The conversations you have with others are responses to sound. Chemicals: People will resist some foods that have a bitter taste, because bitterness means certain alkaloids which are often toxic, especially after consuming in large quantities.
Organisms are capable of producing offspring similar or identical to themselves to maintain species continuity. Reproduction can be either asexual or sexual. Asexual reproduction: Single-celled organisms, such as various bacteria and protists, divide to produce offspring that are identical to themselves, if you disregard genetic mutations. Sexual reproduction: Various vertebrates produce sperm or eggs that contain half of the genetic material. The sperm and egg can then combine to develop a new individual with both maternal and paternal traits.
Organisms can ingest or synthesize various organic substances to make their bodies larger. For example, single-celled organisms make copies of their DNA before the next division, and their volume increase in size. In multicellular organisms, not only does the cell volume increase, but also the cell number increases and some cells differentiate into cells with different functions.
The conditions required for metabolism in an organism (e.g., temperature, pH, ion concentration etc.) are limited to a very narrow range. Organisms maintain the relative stability of internal conditions through a number of regulatory mechanisms, even the external environment changes drastically. For example, human body temperature fluctuates very little during one day, usually varying by at most one degree.
7. Evolution and adaptation to the environment
Organisms produce offspring that may undergo genetic mutations or recombination to acquire new characteristics. Certain traits are better adapted to the environment, so organisms with these traits are easy to outcompete their competitors and their offsprings inherit these genes. The evolution is the process of natural selection, so organisms living on this planet have the ability to adapt to their environment, otherwise they would have been eliminated by nature. The universal law of biological evolution is: the life is from simple to complex and from aquatic to terrestrial.