2.5 Membrane Transport

Describe the mechanisms that organisms use to maintain solute and water balance.

• The selective permeability of membranes allows for the formation of concentration gradients of solutes across the membrane.
• Passive transport is the net movement of molecules from regions of high concentration to regions of low concentration without the direct input of metabolic energy.
• Active transport requires the direct input of energy to move molecules. In some cases, active transport is utilized to move molecules from regions of low concentration to regions of high concentration.

Describe the mechanisms that organisms use to transport large molecules across the plasma membrane.

• The processes of endocytosis and exocytosis require energy to move large substances or large amounts of substances into and out of cells.
  • i. In endocytosis, the cell takes in large molecules and particulate matter by folding the plasma membrane in on itself and forming new (small) vesicles that engulf material from the external environment.
  • ii. In exocytosis, internal vesicles release material from cells by fusing with the plasma membrane and secreting large molecules from the cell.