Cells and Cell Environments

Cell Biology: Prokaryotes, Eukaryotes, and Osmosis

Introduction to Cells

• Cells as Units of Life: Cells are the fundamental, smallest units of life; all living organisms are composed of cells.
• Two Main Cell Types:
  • Prokaryotic Cells: Form prokaryotic organisms (prokaryotes).
  • Eukaryotic Cells: Form eukaryotic organisms (eukaryotes).

Prokaryotic Cells and Organisms

• Taxonomic Domains:
  • Domain Bacteria: Comprises the bacteria, which are single-celled organisms.
  • Domain Archaea: Comprises archaea, which are also single-celled organisms, often found in extreme environments.
• General Characteristics:
  • Significantly smaller than eukaryotic cells, typically ranging from $0.1$ to $5 \mu m$ in diameter.
  • Lack membrane-bound organelles, including a true nucleus. Their genetic material (DNA) is located in a region called the nucleoid.
  • Have a cell wall, a cell membrane, cytoplasm, and ribosomes.
  • Reproduce primarily through binary fission.

Eukaryotic Cells and Organisms

• Taxonomic Domains:
  • Domain Eukarya: Comprises organisms made of eukaryotic cells, including animals, plants, fungi, and protists.
• General Characteristics:
  • Generally larger and more complex than prokaryotic cells, typically ranging from $10$ to $100 \mu m$ in diameter.
  • Possess a true nucleus, which houses their genetic material (DNA) organized into chromosomes.
  • Contain various membrane-bound organelles, each with specialized functions (e.g., mitochondria for energy production, endoplasmic reticulum for protein and lipid synthesis, Golgi apparatus for modification and transport).
  • Reproduce through mitosis for somatic cells and meiosis for germ cells.

Osmosis

• Definition: Osmosis is the net movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.
• Key Principles:
  • Selectively Permeable Membrane: Allows certain molecules (like water) to pass through while restricting others (like solutes).
  • Water Potential: Water moves from an area of higher water potential (lower solute concentration) to an area of lower water potential (higher solute concentration) until equilibrium is reached.
• Types of Solutions (relative to a cell):
  • Isotonic Solution: The solute concentration outside the cell is equal to that inside the cell, resulting in no net water movement.
  • Hypotonic Solution: The solute concentration outside the cell is lower than that inside the cell, causing water to move into the cell.
  • Hypertonic Solution: The solute concentration outside the cell is higher than that inside the cell, causing water to move out of the cell.