Overview
This lecture discusses the main characteristics that define living things, emphasizing the complexity and exceptions in classifying life.
Characteristics of Living Things
- Living organisms are made of one or more cells, as described by cell theory.
- Biological organization exists in levels: cells, tissues, organs, organ systems.
- Homeostasis is the regulation of internal conditions (like temperature and water) for stability.
- Metabolism involves all chemical reactions that obtain and use energy (e.g., photosynthesis, cellular respiration).
- Living things reproduce, either asexually (e.g., bacteria splitting) or sexually (e.g., fertilization in animals).
- Growth and development occur based on genetic material with instructions for these processes.
- Living things respond to internal and external stimuli (e.g., hunger, danger, plants bending toward light).
- Evolution occurs in populations over time, leading to adaptations through natural selection.
Exceptions and Debates
- The precise number and type of life characteristics can vary, and new discoveries may alter definitions.
- Some entities, like viruses, show some but not all characteristics of life and are generally not classified as living.
- Certain extreme or undiscovered organisms challenge existing definitions of life.
- Extraterrestrial life could potentially have different or overlapping characteristics.
Key Terms & Definitions
- Cell Theory — the concept that all living organisms are composed of cells.
- Homeostasis — the process of maintaining stable internal conditions.
- Metabolism — chemical processes that obtain and use energy in organisms.
- Reproduction — production of new organisms; can be sexual or asexual.
- Growth and Development — increase in size and complexity, guided by genetic material.
- Stimulus — a change in environment that elicits a response from an organism.
- Evolution — genetic change in populations over generations.
- Autotroph — organism that produces its own food (e.g., via photosynthesis).
- Heterotroph — organism that obtains energy by consuming other organisms.
Action Items / Next Steps
- Reflect on examples of living and nonliving things using these characteristics.
- Optional: Watch the Amoeba Sisters’ virus video for discussion on viruses and life classification.