Cell Structure and Membrane Transport

Cell Structure Review

Plant and Animal Cells

• Labeling Cell Diagrams

  • Animal Cell Components:

  • Cytoplasm

  • Lysosome

  • Rough Endoplasmic Reticulum (Rough ER)

  • Vacuole

  • Mitochondria

  • Nucleus

  • Plant Cell Components:

  • Cell membrane

  • Rough ER

  • Nucleolus

  • Smooth Endoplasmic Reticulum (Smooth ER)

  • Mitochondria

  • Central Vacuole

  • Cell wall

  • Chloroplast

  • Golgi body

  • Peroxisome

Membrane Transport Mechanisms

• Endocytosis: The process by which the cell membrane engulfs substances to bring them into the cell.

  • Types of Endocytosis:
  • Pinocytosis: Engulfs small droplets of extracellular fluid and dissolved substances.
  • Phagocytosis: Engulfs larger particles, such as bacteria; occurs in specialized cells.
  • Receptor-assisted Endocytosis: Involves the intake of specific molecules through receptor proteins.

• Exocytosis: The process where vesicles fuse with the cell membrane to expel substances out of the cell.

Types of Transport

• Passive Transport:

  • No energy required.
  • Follows the concentration gradient (from high concentration to low concentration).
  • Diffusion: Movement of molecules from higher to lower concentration.
  • Osmosis: The diffusion of water across a semi-permeable membrane.
    • Isotonic: Equal water concentration inside and outside the cell.
    • Hypotonic: Higher water outside the cell; water moves into the cell.
    • Hypertonic: Higher water inside the cell; water moves out of the cell.
  • Facilitated Diffusion: Requires transport proteins to help move substances too large to pass directly through the membrane.

• Active Transport:

  • Requires energy (often from ATP) to move substances against their concentration gradient.
  • Active transport functions through specific proteins that can recognize and transport only certain types of molecules or ions.
  • Example: Carrier proteins for glucose, channel proteins for ions.

Cell Membrane Structure

• Phospholipid Bilayer: Composed of hydrophobic (water-fearing) tails and hydrophilic (water-loving) heads.
  • Selectively Permeable: Allows certain substances to pass while blocking others.
  • Embedded Proteins:
  • Channel Proteins: Provide passage for small hydrophilic molecules.
  • Carrier Proteins: Change shape to transport larger molecules.

Key Concepts

• Gradient: A term describing a difference between two adjacent areas (e.g., concentration gradient).
• Energy Transfer: ATP is essential for active transport; energy is released when a phosphate group is cleaved from ATP.

Summary of Mechanisms

• Diffusion:
  • Follows concentration gradient, requires no energy.
• Osmosis:
  • Specific to water molecules, requires no energy.
• Facilitated Diffusion:
  • Needs transport proteins, requires no energy.
• Active Transport:
  • Moves against gradient, requires energy.
• Endocytosis & Exocytosis:
  • Processes for material intake and expulsion, can involve vesicles.