1.4

Membrane Transport

Cell Membrane

Acts as a barrier controlling substances entering and leaving the cell, allowing passive or active movement.

Passive Movement

Occurs without energy expenditure, driven by chemical and electrical gradients, forming an electrochemical gradient.

Diffusion

Molecules move from high to low concentration, facilitated by lipid-soluble molecules or pores in the membrane.

Osmosis

Movement of water from low to high solute concentration areas through aquaporins, generating osmotic pressure.

Facilitated Diffusion

Uses transport proteins for lipid-insoluble or large molecules, like glucose, enhancing their movement.

Ion Channels

Integral proteins aiding the facilitated diffusion of ions through selective channels in the cell membrane.

Active Transport

Uses energy, like the Na+/K+-ATPase pump, to move ions against gradients, essential for cell function.

Primary Active Transport

Directly uses ATP to transport substances, like the Na+/K+-ATPase pump.

Secondary Active Transport

Derives energy from primary transport, like cotransport (symport) or counter-transport (antiport) systems.

Endocytosis

Encloses molecules outside the cell in vesicles through processes like pinocytosis and phagocytosis.

Exocytosis

Releases intracellular substances into the extracellular space, important for removing debris and hormone secretion.

Membrane Potential

Voltage difference between cell interior and exterior, crucial for nerve impulses, muscle contractions, and hormone secretion.

Diffusion Potential

Voltage generated by ions diffusing across the membrane due to permeability and concentration gradients.