This document discusses the definition of life and its key characteristics. It notes that life consists of self-sustaining processes that can grow, react to stimuli, metabolize energy, and reproduce. There are different types of cells (prokaryotic and eukaryotic) that reproduce through cell division and pass on genes. Organisms maintain homeostasis, are composed of cells, have life cycles involving metabolism, growth, adaptation, response, and reproduction. New lifeforms evolve from common ancestors through genetic variation and natural selection. Estimates suggest there are between 3 million to over 100 million distinct species on Earth today.

1. What is Life?

2. hi
• What is life?
• For other uses, see Life (disambiguation). For "Life" in the personal
sense, see Personal life and Everyday life.
• For technical reasons, "Life #9" redirects here. For the song, see Life
Number 9.

3. • as signaling and self-sustaining processes, from matter that does not, and is
defined by the capacity for growth, reaction to stimuli, metabolism, energy
transformation, and reproduction.[2][3] Various forms of life exist, such
as plants, animals, fungi, protists, archaea, and bacteria. Biology is
the science that studies life.
• The gene is the unit of heredity, whereas the cell is the structural and
functional unit of life.[4][5] There are two kinds of
cells, prokaryotic and eukaryotic, both of which consist
of cytoplasm enclosed within a membrane and contain
many biomolecules such as proteins and nucleic acids. Cells reproduce
through a process of cell division, in which the parent cell divides into two
or more daughter cells and passes its genes onto a new generation,
sometimes producing genetic variation.

4. • Organisms, or the individual entities of life, are generally thought to be open
systems that maintain homeostasis, are composed of cells, have a life cycle,
undergo metabolism, can grow, adapt to their environment, respond to stimuli,
reproduce and evolve over multiple generations. Other definitions sometimes
include non-cellular life forms such as viruses and viroids, but they are usually
excluded because they do not function on their own; rather, they exploit the
biological processes of hosts.[6][7]
• Abiogenesis, also known as the origin of life, is the natural process of life arising
from non-living matter, such as simple organic compounds. Since its primordial
beginnings, life on Earth has changed its environment on a geologic time scale,
but it has also adapted to survive in most ecosystems and conditions.
New lifeforms have evolved from common
ancestors through hereditary variation and natural selection, and today,
estimates of the number of distinct species range anywhere from 3 million to
over 100 million.[3][8]

5. Death
• Death is the permanent termination of all biological processes which
sustain an organism, and as such, is the end of its life. Extinction is the
term describing the dying-out of a group or taxon, usually a species.
Once extinct, the extinct species or taxon cannot come back to
life. Fossils are the preserved remains or traces of organisms.