2.7 Tonicity and Osmoregulation

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

• External environments can be hypotonic, hypertonic, or isotonic to internal environments of cells. Movement of water can also be described as moving from hypotonic to hypertonic regions. Water moves by osmosis from regions of high water potential to regions of low water potential. Relevant equation: Water Potential: ps where: p = pressure potential s = solute potential

Explain how osmoregulatory mechanisms contribute to the health and survival of organisms.

• Growth and homeostasis are maintained by the constant movement of molecules across membranes.
• Osmoregulation maintains water balance and allows organisms to control their internal solute composition and water potential. Water moves from regions of low osmolarity or solute concentration to regions of high osmolarity or solute concentration. Relevant equation: Solute Potential of a Solution: s=−iCRT where: i = ionization constant C = molar concentration R = pressure constant R Lb ars molK0.0831 = T = temperature in Kelvin (°C + 273)