1. Organization: Living things are highly organized, with specialized structures (cells, tissues, organs) that work together to maintain life.
2. Metabolism: They carry out chemical reactions to obtain and use energy, synthesize new molecules, and eliminate waste. This includes processes like respiration, photosynthesis, and digestion.
3. Growth and Development: Living organisms increase in size and complexity over time, following a specific pattern of development.
4. Response to Stimuli: They react to changes in their environment, both internal and external, to maintain homeostasis.
5. Reproduction: They produce offspring, passing on their genetic information. This can be sexual or asexual reproduction.
6. Adaptation: Living things evolve over time, adapting to their environment through natural selection.
7. Homeostasis: They maintain a stable internal environment, despite external changes.
It's important to note that these are not absolute rules, and there are exceptions to each of these criteria. For example, viruses are considered by some to be living organisms, but they lack many of these characteristics, particularly metabolism and independent reproduction.
Ultimately, defining life is a complex and ongoing discussion. Biologists use these characteristics as a framework for understanding the diversity and complexity of living organisms.