Unit 2 · 2.7 — Tonicity and Osmoregulation [cite: 9, 28]

14 learning items · ~1.15% exam weight (unit share)

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Concept: Water moves passively via osmosis from areas of high water potential (low solute concentration) to areas of low water potential (high solute concentration) [cite: 14, 34].
Equation: Equation/Process: Water Potential: $\Psi = \Psi_s + \Psi_p$ [cite: 14, 31].
Equation: Equation/Process: Solute Potential: $\Psi_s = -iCRT$ [cite: 14, 31, 34].
Vocabulary: Hypertonic — a solution possessing a higher concentration of non-penetrating solutes compared to the cell, causing water to leave the cell [cite: 13, 14].
Vocabulary: Hypotonic — a solution possessing a lower concentration of non-penetrating solutes compared to the cell, causing water to enter the cell [cite: 13, 14].
Vocabulary: Isotonic — solutions with equal solute concentrations, resulting in dynamic equilibrium with no net movement of water [cite: 13, 14].
Vocabulary: Osmoregulation — the active maintenance of constant osmotic pressure and water balance in the fluids of an organism [cite: 13].
Vocabulary: Plasmolysis — the lethal shrinking of a plant cell's cytoplasm away from the cell wall when placed in a hypertonic environment [cite: 14].
Lab: Lab Skill: AP Biology Required Investigation — Diffusion and Osmosis: Calculate $\Psi_s$ using the ionization constant ($i$), molar concentration ($C$), pressure constant ($R$), and temperature in Kelvin ($T$) from experimental plant tissue data [cite: 6, 31, 34, 35].
Concept: Describe how concentration gradients drive the movement of water and solutes across biological membranes.
Concept: Explain how osmoregulatory mechanisms allow organisms to survive in varying environmental tonicities.
Equation: $P s i = P s i_{p} + P s i_{s}; w a t er p o t e n t ia l d e t er min es t h e d i r ec t i o n o f os m os i s f r o mhi g h t o l o w p o t e n t ia l .$
Concept: Explain how the continuous movement of molecules across membranes is necessary for maintaining organismal growth and homeostasis.
Equation: $P s i_{s} = - i C R T; c a l c u l a t esso l u t e p o t e n t ia l ba se d o ni o ni z a t i o n, co n ce n t r a t i o n, t h e p r ess u r eco n s t an t, an d t e m p er a t u r e .$

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