Characteristics of Living Things

Introduction to Living Things

• Biology: The study of living things.

• Living vs Non-Living: Distinction between biotic (living) and abiotic (non-living) factors.

• Seven Characteristics of Living Things: Necessary to define something as alive; absence of even one characteristic indicates non-living.

Characteristics of Living Things

1. Universal Genetic Code

• All living organisms use DNA to store information necessary for living, growing, and reproducing.

• Presence of DNA is a significant indicator of life, but must also have other characteristics to be considered living.

2. Growth and Development

• All living things experience growth, starting as a single cell that divides and differentiates.

• Different growth stages in organisms, e.g., larvae to adult transformations in some species.

• Growth can be simple (cellular increase) or complex (development through various life stages).

3. Response to Environment

• Organisms respond to stimuli in their environment (e.g., light, danger, nutrients).

• Stimulus is any signal that prompts a reaction from the organism; responses can be subtle or pronounced.

• Even simple organisms have mechanisms to respond to environmental stimuli.

4. Reproduction

• All living things reproduce; methods can vary.

• Asexual Reproduction: One cell divides into two, producing clones (e.g., bacteria).

• Sexual Reproduction: Combining genetic information from two parents to create genetically varied offspring, which enhances survival chances amid environmental changes.

5. Homeostasis

• Living organisms maintain stable internal conditions, a process known as homeostasis.

• Examples include regulating water balance, hunger, and fatigue.

• Homeostasis involves feedback mechanisms to ensure internal environments remain suitable for survival.

6. Metabolism

• Living things acquire and utilize materials and energy for growth, development, and reproduction.

• Metabolism comprises all chemical processes occurring within an organism.

• Requires intake of nutrients to provide the energy necessary for cellular processes and growth.

7. Cellular Structure

• All living organisms are composed of cells, which are the basic units of life.

• Can be unicellular (single-celled organisms) or multicellular (like the human body, which contains trillions of cells).

• Cells must perform vital functions such as responding to stimuli and reproducing.

Viruses: A Unique Case

• Viruses blur the lines between living and non-living due to their unique characteristics:

  • Very small and capable of infecting hosts but cannot reproduce independently.

  • Require a host cell to replicate by commandeering the host's cellular machinery.

• Antibiotics do not affect viruses as they are not considered living organisms.

Conclusion

• Understanding the characteristics of living things helps differentiate between what is truly alive and what is not.

• Observing these characteristics allows for the classification of entities in the biological world.