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

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.