chapter 3.3

• phospholipids with embedded protiends make up the membrane surrounding all cells
• cell membrane controls the movement of substances into and out of cells
• homeostasis: the maintenance of a constant internal environment despite changes in the external environment
• the hydrophobic interior of the lipid bilayer prevents ions charged polar from moving across it
• diffusion: the net amount of molecules from areas of higher to lower concentration as a result of their random thermal motion
• when there is no longer a concentration gradient, net movement stops but random motion of molecules in both directions continue
• passive transport: occurs when molecules move across a cell membrane by diffusion
• facilitated diffusion: diffusion across a cell membrane through a transmembrane protein, such as a channel or carrier
• channel protein: a transporter that facilitates movement of molecules through the membrane
• carrier protein: a transporter that facilitates movement of molecules across a cell membrane
• aquaporins: a protein channel that allows water to cross the cell membrane more readily than by diffusing though the lipid bilayer
• osmosis: the net movement of solvent, such as water, across a selectively permable
• active transport: the movement of substances across a cell membrane against an electrochemical gradient, requiring an input of energy
• primary active transport: active transport that uses energy of ATP directly in this manner
• ATP: adenosine triphosphate.
• ADP: adenosine disphosphate
• Pi: inorganic phosphate
• secondary active transport is the movement of ions across the membrane by using energy from respiration
• electrochemical gradient: gradient of the concentration of a substance across a cell membrane
• contractile vacoules: organelles that contract to move substances in and out of the cell
• turgor pressure: the force exerted by water pressing against an object
• vacuoles: absorbs water and contributes to turgor pressure
• cytoskeleton: internal protein scaffold