Characteristics of Living Things

Introduction

• Toys that grow in water increase in size but are not alive.
• Biological growth and development differ from mere increase in size.
• Definition of life is complex and debated among biologists.
• Characteristics of life help explore what it means for an organism to be alive.
• Disclaimer: Characteristics can change and are debated. Not a definitive list.

Key Characteristics of Life

Organization

• Cell Theory: Living organisms are made of cells.
  • Unicellular organisms: Made of one cell.
  • Multicellular organisms: Made of multiple cells, organized into tissues, organs, and organ systems.
    • Example: Pony made of many cells.
• Bathtub-grown pony has no cells.

Homeostasis

• Importance of maintaining a regulated balance for biological processes.
  • Example: Enzymes need certain pH ranges.
  • Maintaining temperature and water concentration is crucial.
• Feedback systems in organisms maintain homeostasis.
  • Example: Amoeba relies on cell membrane.
• Bathtub-grown pony does not maintain homeostasis.

Metabolism

• Living organisms must capture and use energy for processes, including homeostasis.
  • Example: Plants use photosynthesis to make glucose.
  • Animals eat and digest to obtain glucose, which is used in cellular respiration to make ATP energy.
• Bathtub pony has no metabolism.

Reproduction

• Simple reproduction: Unicellular bacteria copy DNA and split.
• Complex reproduction: Involves sperm and egg combining to form a zygote.
  • Example: Real pony reproduction.
• Bathtub-grown pony cannot reproduce.

Growth and Development

• Genetic material codes for development and growth.
  • Example: Baby pony grows into an adult pony.
• Bathtub-grown pony only grows due to water, not genetic instructions.

Response to Stimuli

• Living organisms respond to internal and external stimuli.
  • Example: Hunger (internal) and danger (external) sensed by a pony.
  • Plants respond to light by bending towards it.
• Bathtub-grown pony does not respond to stimuli.

Evolution

• Life as a "self-sustaining system capable of Darwinian evolution."
• Gene frequencies in populations change over time due to natural selection.
  • Traits providing reproductive fitness are selected for.
  • Traits lowering fitness are selected against.
• Bathtub-grown pony cannot evolve as it does not reproduce.

Challenges and Exceptions

• Characteristics of life can be adjusted and have exceptions.
  • Example: Viruses can reproduce and evolve but lack other characteristics of life.
• Potential for extraterrestrial life might not follow Earth's characteristics of life.

Conclusion

• Characteristics of life are intriguing and raise many questions.
• Stay curious and open to new information.

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