Question

How many criteria does a living organism have to meet to be classified as living? Justify your answer.

Answer 1

1. Living Things are Composed of Cells:
Single-cell organisms have everything they need to be "self-sufficient". In multicellular organisms, specialization increases until some cells do only certain things.
2. Different Levels of Organization:
Living things must be able to organize simple substances into complex ones.
Living things organize cells at several levels:
Tissue - a group of cells that perform a common function.
Organ - a group of tissues that perform a common function.
Organ system - a group of organs that perform a common function.
Organism - any complete living thing
3. Living Things Use Energy:
Living things take in energy and use it, for maintenance and growth.
4. Living Things Respond To Their Environment:
Living things will make changes in response to a stimulus in their environment. A behavior is a complex set of responses.
5. Living Things Grow:
Cell division - the orderly formation of new cells.
Cell enlargement - the increase in size of a cell. Cells grow to a certain size and then divide.
An organism gets larger as the number of its cells increases.
6. Living Things Reproduce:
Reproduction is not essential for the survival of individual organisms, but must occur for a species to survive.
All living things reproduce in one of the following ways:
Asexual reproduction - Producing offspring without the use of gametes.
Sexual reproduction - Producing offspring by the joining of sex cells.
7. Living Things Adapt To Their Environment:
Adaptations are traits giving an organism an advantage in a certain environment.
Variation of individuals is important for a healthy species.