Water, Solvation, and Osmoregulation (IB Biology D2.3)

Vocabulary flashcards summarizing solvation, tonicity, osmosis, water potential, and medical/plant applications of water movement.

Universal solvent

A substance, such as water, that can dissolve many different solutes, enabling countless biological reactions.

Aqueous solution

A liquid mixture in which water acts as the solvent.

Solvent

The component of a solution that dissolves the solute; in biology, water is the most common example.

Solute

The substance that is dissolved in a solution.

Polar covalent molecule

A molecule, like water, with uneven electron distribution, creating partial positive and negative charges.

Hydrogen bond

A weak attraction between a hydrogen atom carrying a partial positive charge and an electronegative atom, important in water’s properties.

Polar substance

A compound (e.g., salts, alcohols, acids) that readily dissolves in water due to charge separation.

Non-polar substance

A compound (e.g., fats, oils, lipids) that is insoluble in water because it lacks partial charges.

Solvation (hydration)

The interaction of water molecules with solute particles during dissolution.

Steps of solvation

1) Solute particles separate, 2) Water molecules separate, 3) Water surrounds solute to form a solution.

Hydrated ion

An ion surrounded by a shell of orientated water molecules, as occurs with Na⁺ or Cl⁻ in solution.

Sodium chloride dissolution

Na⁺ is encircled by water’s δ− oxygen, Cl⁻ by δ+ hydrogens, producing a highly soluble solution.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water.

Hypertonic solution

Environment with higher solute (lower water) concentration than another solution; water flows toward it.

Hypotonic solution

Environment with lower solute (higher water) concentration; water flows out of it toward more concentrated areas.

Isotonic solution

Solutions with equal solute and water concentrations, resulting in no net water movement.

Osmosis

Passive transport of water across a selectively permeable membrane from high to low water potential.

Aquaporin

Membrane protein channel that accelerates water transport through the hydrophobic lipid bilayer.

Turgid cell

Plant cell swollen with water, pressing its membrane against the cell wall, generating turgor pressure.

Plasmolysis

Shrinkage of plant cell cytoplasm away from the cell wall due to water loss in a hypertonic environment.

Crenation

Shriveling of an animal cell, such as a red blood cell, when water exits in a hypertonic solution.

Hemolysis

Bursting of an animal cell after excessive water intake in a hypotonic environment.

Contractile vacuole

Organelle in some aquatic protists that expels excess water to prevent swelling in hypotonic conditions.

Dehydration (human)

Condition where water loss causes cell shrinkage, light-headedness, muscle cramps, and organ malfunction.

Hyponatremia

Dangerously low blood sodium from excess water intake, leading to cell swelling and possible damage.

Hydrostatic pressure

Force exerted by fluid in a confined space; in plants, it contributes to turgor pressure.

Turgor pressure

Internal pressure exerted by water inside the vacuole against the plant cell wall, essential for rigidity.

Water potential (Ψw)

Potential energy of water per unit volume; zero for pure water, always negative when solutes are present.

Solute potential (Ψs)

Component of water potential that becomes more negative as solute concentration increases.

Pressure potential (Ψp)

Component of water potential generated by turgor; positive in living cells, negative in xylem.

Water potential equation

Ψw = Ψs + Ψp; total water potential equals solute potential plus pressure potential.

Transpiration pull

Negative pressure created in xylem as water evaporates from stomata, drawing water upward.

Halophyte

Plant adapted to high-salinity environments via salt sequestration, excretion, or compartmentalization.

Salt gland

Specialized structure in some halophytes that excretes excess salt to maintain water uptake.

Normal saline

Sterile 0.9% NaCl solution isotonic to body fluids, commonly used in IV therapy.

Lactated Ringer’s solution

Isotonic IV fluid containing Na⁺, K⁺, Ca²⁺, Cl⁻, and lactate, used to restore fluid and electrolyte balance.

Dextrose in water (D5W)

Isotonic IV solution of 5% glucose, providing both fluids and energy.

Physiological saline

Isotonic NaCl solution used for contact lens storage and eye irrigation.

Organ preservation solution

Isotonic fluid in which donor organs are immersed to prevent osmotic damage before transplantation.

Cytoplasm

Aqueous interior of cells where solutes are dissolved, creating an intracellular solution.

Dynamic equilibrium (osmosis)

State in isotonic conditions where water enters and exits the cell at equal rates.

Hydrated shell

Layer of oriented water molecules surrounding a dissolved ion or polar molecule.

Plasmolytic weed killer

Mixture of salt, vinegar, and detergent that draws water out of plant cells, causing death by plasmolysis.

Wilted plant

Plant whose cells have low turgor pressure due to water loss, leading to drooping leaves and stems.

Aquaporin gating

Regulation of water channel opening and closing, under study for improving crop salt tolerance.