A1.1 Water - Pre-IB Biology Work

Water (H₂O) consists of two hydrogen atoms covalently bonded to one oxygen atom.

Covalent bonds exist, involving shared electrons. However, in water, electrons are not shared equally.

Because oxygen has higher electronegativity than hydrogen, pulling shared electrons closer and creating a partial negative charge (δ–) on oxygen and partial positive charges (δ+) on the hydrogen atoms.

It allows water to form weak interactions (e.g., hydrogen bonds) with other polar molecules or ions; δ– regions attract δ+ regions and vice versa.

Hydrogen bonds are intermolecular attractions formed when a δ+ hydrogen atom of one molecule is attracted to a δ– fluorine, oxygen, or nitrogen atom of another molecule.

Thermal properties (e.g., high specific heat and boiling point), cohesive properties, and solvent abilities.

Because F, O, and N are highly electronegative, which increases the strength of the attraction.

Hydrogen bonding causes cohesion, allowing water molecules to stick to each other.

Cohesion creates surface tension, enabling water to resist small external forces.

They use long, hairy legs to trap air, distribute their weight, increase buoyancy, and walk on the water surface due to high surface tension.

Water’s ability to stick to other polar or charged surfaces via polar associations.

It is the movement of water against gravity in narrow tubes or pores, caused by adhesion to surfaces and cohesion between water molecules.

Water moves from roots to leaves through xylem vessels due to a pressure gradient created by osmosis into roots and evaporation from leaves. This movement relies on cohesion and adhesion.

Soil type affects the strength of capillary action, impacting agricultural efficiency and irrigation.

The process where solvent molecules surround and interact with solute molecules.

A solute is a substance (usually a solid) that dissolves in a solvent. Soluble substances dissolve, while insoluble substances do not.

Because it can dissolve many substances that contain ions or electronegative atoms due to its polarity.

Its δ+ and δ– regions form hydration shells around charged/polar solutes.

It dissolves many substances, increasing collision rates with enzymes and facilitating chemical reactions. It also absorbs heat from exothermic reactions and helps maintain pH and acid-base balance.

Hydrophilic substances are polar/ionic and dissolve in water; hydrophobic substances are non-polar (e.g., lipids) and do not dissolve.

Blood plasma transports amino acids, simple sugars, urea, and small amounts of gases (O₂ and CO₂). Lipids, being insoluble, are transported as lipoproteins.

Xylem transports mineral ions; phloem transports dissolved nutrients (e.g., sugars). Lipids may be conjugated to amino acids and transported via the phloem.

Buoyancy, viscosity, thermal conductivity, and specific heat capacity.

Buoyancy is the upward force exerted by a medium. Water is denser than air and applies greater upward force, allowing lighter objects to float.