There are many ways to define the characteristics of a living creature, and the number of characteristics can vary depending on the level of detail. However, five core characteristics are widely accepted:

1. Organization: Living things are highly organized, with specialized structures (cells, tissues, organs) that work together to perform specific functions.

2. Metabolism: Living things carry out chemical reactions to obtain and use energy. This includes processes like respiration, photosynthesis, and digestion.

3. Growth and Development: Living organisms increase in size and complexity over time. This involves processes like cell division and differentiation.

4. Response to stimuli: Living things react to changes in their environment, such as temperature, light, or the presence of food or predators. This is known as irritability.

5. Reproduction: Living things produce offspring, ensuring the continuity of their species.

These characteristics, taken together, define what it means to be alive.