IB DP Biology D2.3 Water potential Study Notes - New Syllabus -2025
IB DP Biology D2.3 Water potential Study Notess – New syllabus 2025
IB DP Biology D2.3 Water potential Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of
- What factors affect the movement of water into or out of cells?
- How do plant and animal cells differ in their regulation of water movement?
Standard level and higher level: 2 hours
Additional higher level: 2 hours
D2.3.1—Solvation with water as the solvent
Solvation is the combination of a solvent with the molecules or ions of a solute. They depend on water’s polarity, with a partial negative charge at the oxygen pole and partial positive charge at the hydrogen pole of the molecule.
- Polar solutes dissolve due to attraction between the partial positive and negative charges on water molecules and solute molecules.
- Positively charged ions are attracted to the partial negative oxygen pole of water.
- Negatively charged ions are attracted to the partial positive hydrogen pole of water.
Because of these attractions, water molecules form shells around many types of ion and charged molecule, preventing them from precipitating by clumping together. Cytoplasm is a complex mixture of dissolved substances in which the chemical reactions of metabolism occur.
- Ionic bonds between sodium and chloride ions are broken when sodium chloride dissolves in water.
- Oxygen in water molecules is attracted to positively charged ions (cations).
- Hydrogen in water molecules is attracted to negatively charged ions (anions).
D2.3.2—Water movement from less concentrated to more concentrated solutions
The particles in a liquid can move, but because of intermolecular attractions, they do not separate from each other completely unless the liquid is changing into a gas. As water molecules change position, hydrogen bonds are repeatedly broken and formed. However, at any given time, many bonds exist, so there is a strong overall attraction between the water molecules.
Intermolecular attractions between solutes and water are even stronger, which explains how solutions form. These attractions restrict the movement of water molecules, so solutions are more viscous than pure water. Solute-water attractions influence the movement of water molecules between solutions. If water can move between two solutions, there is always movement in both directions. But more water molecules will move from the less concentrated solution to the more concentrated than in the other direction. There is therefore a net movement of water from the less concentrated to the more concentrated solution.
Osmosis is net movement of water across a membrane due to the attractions between solutes and water. Solutes are osmotically active if intermolecular attractions form between them and water. Sodium, potassium, and chloride ions and glucose are all osmotically active.
The following three terms are useful when describing the relative tendency of water to move between solutions due to the concentrations of osmotically active solutes:
- There is a net movement of water from a hypotonic solution to a hypertonic solution because the hypertonic solution has a higher concentration of osmotically active solutes.
- There is no net movement of water between two isotonic solutions because there is no difference between their concentrations of osmotically active solutes, even though individual molecules move between them. This is known as dynamic equilibrium.
The concentration of a solute per unit volume of solution. The volume is expressed in cubic meters (m³), liters (L), or dm³. Units are sometimes written as % (w/v), mole per liter (1 mol = 1 L = 1dm³). Negative indices indicate “per unit volume” (m⁻³ or L⁻¹). The volume unit (L or l = 1dm³).