Describe the roles of each of the components of the cell membrane in maintaining the internal environment of the cell./Explain how concentration gradients affect the movement of molecules across membranes.

phospholipids

have both hydrophilic and hydrophobic regions. The hydrophilic phosphate regions of the phospholipids are oriented toward the aqueous external or internal environments, while the hydrophobic fatty acid regions face each other within the interior of the membrane.

endocytosis

require energy to move large molecules

exocytosis

require energy to move large molecules internal vesicles fuse with the plasma membrane and secrete large macromolecules out of the cell. the cell takes in macromolecules and particulate matter by forming new vesicles derived from the plasma membrane.

active transport

requires the direct input of energy to move molecules from regions of low concentration to regions of high concentration.

Passive transport

the net movement of molecules from high concentration to low concentration without the direct input of metabolic energy does not require energy plays a primary role in the import of materials and the export of wastes.

proteins

Embedded proteins can be hydrophilic, with charged and polar side groups, or hydrophobic, with nonpolar side groups.

active transport

Energy-requiring process that moves material across a cell membrane against a concentration difference Membrane proteins are necessary for active transport. Metabolic energy (such as from ATP) is required for active transport of molecules and/or ions across the membrane and to establish and maintain concentration gradients.

Explain how concentration gradients affect the movement of molecules across membranes.

External environments can be hypotonic, hypertonic or isotonic to internal environments of cells— a. Water moves by osmosis from areas of high water potential/low osmolarity/low solute concentration to areas of low water potential/high osmolarity/high solute concentration.

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

The selective permeability of membranes allows for the formation of concentration gradients of solutes across the membrane.

Explain how the structure of a molecule affects its ability to pass through the plasma membrane.

Membrane proteins are required for facilitated diffusion of charged and large polar molecules through a membrane— a. Large quantities of water pass through aquaporins.

Charged ions

Membranes may become polarized by movement of ions across the membrane. including Na+ and K+, require channel proteins to move through the membrane. The Na+/K+ ATPase contributes to the maintenance of the membrane potential.