Summary of Chapter 20: The Nature of Living Things

Five Characteristics of Living Things:

1. Metabolism:

• Ability for chemical reactions to sustain life (e.g., humans metabolizing food, plants absorbing water and sunlight).

1. Generation:

• Living things can reproduce and create copies (not necessarily clones).

1. Responses:

• Interaction with the environment and stimuli (e.g., flinching from pain).

1. Control:

• Maintaining homeostasis (balance within internal and external environments).

1. Structural Components:

• All living things have identifiable structures that sustain life.

Biological Organization:

• Ranges from atomic to universal levels, focusing on cells for this chapter.

Discovery of the Cell:

• Robert Hooke coined the term "cell" in 1665 while observing cork under a microscope.
• Historical context: 1665, England, a time dominated by religious beliefs over scientific inquiry.

Cell Theory:

• Developed by Schwann, Schleiden, and Virchow:

1. All living things are composed of cells.
2. New cells arise from existing cells.
3. Cells are the fundamental unit of life.

Types of Cells:

• Prokaryotic (simpler, e.g., bacteria) vs. Eukaryotic (complex, e.g., human body cells).

Cell Functionality:

• Major components of eukaryotic cells include:
  • Cell Membrane:
  • Semipermeable, allowing selective movement of substances in and out.
  • Mitochondria:
  • Energy production center of the cell.
  • Nucleus:
  • Contains DNA and regulates cell activity.
  • Endoplasmic Reticulum:
  • Important for protein synthesis.

Cell Division:

• Mitosis:
  • Asexual reproduction; one division creates two identical cells.
• Meiosis:
  • Sexual reproduction; two divisions create four genetically diverse cells.
  • Ensures genetic diversity by halving genetic material from parents.

Conclusion:

• Cells are fundamental components of all living beings. Understanding cells is crucial to understanding life itself.