Cell Membrane Transport Mechanisms to Know for AP Biology

Cell membrane transport mechanisms are vital for maintaining cellular function and homeostasis. They include passive processes like diffusion and osmosis, as well as active transport methods that require energy. Understanding these processes is key in AP Biology.

1. Passive transport

   • Movement of molecules across the cell membrane without the use of energy (ATP).
   • Relies on concentration gradients; substances move from areas of high concentration to low concentration.
   • Includes processes like simple diffusion, facilitated diffusion, and osmosis.

2. Simple diffusion

   • The process by which small, nonpolar molecules (e.g., O2, CO2) pass directly through the lipid bilayer.
   • Does not require any transport proteins or energy.
   • Rate of diffusion is influenced by factors such as temperature, size of molecules, and concentration gradient.

3. Facilitated diffusion

   • Involves the use of specific transport proteins to help larger or polar molecules (e.g., glucose, ions) cross the membrane.
   • Still a passive process; does not require energy.
   • Can be saturated, meaning there is a maximum rate of transport when all transport proteins are occupied.

4. Osmosis

   • The diffusion of water molecules across a selectively permeable membrane.
   • Water moves from areas of low solute concentration to areas of high solute concentration.
   • Important for maintaining cell turgor pressure and overall homeostasis.

5. Active transport

   • Movement of molecules against their concentration gradient, requiring energy (ATP).
   • Allows cells to maintain concentrations of ions and other substances that differ from their surroundings.
   • Essential for processes like nutrient uptake and waste removal.

6. Sodium-potassium pump

   • A specific type of active transport that moves sodium ions out of the cell and potassium ions into the cell.
   • Helps maintain the electrochemical gradient essential for nerve impulse transmission and muscle contraction.
   • Operates by using ATP to transport three sodium ions out for every two potassium ions in.

7. Endocytosis

   • The process by which cells engulf external substances, forming vesicles to bring them into the cell.
   • Includes phagocytosis (cell eating) and pinocytosis (cell drinking).
   • Important for nutrient uptake, immune response, and cellular signaling.

8. Exocytosis

   • The process of vesicles fusing with the plasma membrane to release their contents outside the cell.
   • Used for the secretion of hormones, neurotransmitters, and waste products.
   • Plays a key role in communication between cells and maintaining membrane integrity.

9. Vesicular transport

   • Involves the movement of materials in and out of cells via vesicles.
   • Includes both endocytosis and exocytosis.
   • Allows for the transport of large molecules and particles that cannot pass through the membrane directly.

10. Ion channels

    • Protein structures that allow specific ions (e.g., Na+, K+, Ca2+, Cl-) to pass through the membrane.
    • Can be gated (open or close in response to signals) or non-gated (always open).
    • Critical for generating action potentials in neurons and muscle cells, contributing to cellular signaling and homeostasis.