A1.1 Water and its properties

Vocabulary flashcards covering key water-related concepts, properties, and biological implications from the notes.

Water

A polar molecule essential for life; a universal solvent and medium for metabolism, with hydrogen bonding, high surface tension, cohesion, and adhesion that support many biological processes.

Hydrogen bond

A weak intermolecular force between a slightly positive hydrogen atom in one polar molecule and a slightly negative atom in another polar molecule; crucial for water's properties.

Polar covalent bond

A covalent bond with unequal sharing of electrons, giving partial charges; in water, oxygen is partially negative and hydrogen is partially positive.

Cohesion

Mutual attraction between water molecules due to hydrogen bonding, enabling continuous water columns in plants and other structures.

Adhesion

Attraction between water molecules and polar or charged surfaces, contributing to wetting and capillary movement.

Capillary action

Movement of water through narrow spaces driven by adhesion to surfaces and cohesion between water molecules.

Surface tension

Energy required to increase the surface area of a liquid; water has high surface tension due to hydrogen bonding, allowing phenomena like water striders on a pond.

Buoyancy

Upward force on a submerged object equal to the weight of the displaced fluid; determines whether the object floats or sinks based on density.

Density

Mass per unit volume; affects buoyancy and how organisms behave in water (e.g., tissues have densities near that of water).

Viscosity

A measure of a fluid’s resistance to flow; water is relatively low in viscosity, while seawater is higher due to dissolved salts.

Thermal conductivity

The rate at which heat passes through a material; water conducts heat more effectively than fats/oils but less than metals, aiding heat distribution.

Specific heat capacity

The amount of heat required to raise the temperature of 1 g of a substance by 1°C; for water it is 4.18 J g⁻¹ K⁻¹, contributing to thermal stability.

Hydrophilic

Substances that are attracted to and dissolve in water (polar or charged) and form hydration shells.

Hydrophobic

Substances that are not attracted to water (non-polar); insoluble in water but may dissolve in non-polar solvents.

Solvent

The dissolving medium; water is a common solvent in biology, forming hydration shells around solutes.

Solute

A substance dissolved in a solvent (e.g., sugars, amino acids, ions).

Hydration shell

A shell of water molecules surrounding a dissolved ion or polar molecule, stabilizing it in solution.

Xylem

Plant vascular tissue that transports water from roots to leaves; water columns in xylem rely on cohesion and tension.

Cohesion-tension theory

Idea that water is pulled upward in xylem by tension created by evaporation at leaves, with cohesion maintaining the water column.

Resurrection plant

Desiccation-tolerant plants (e.g., Selaginella lepidophylla) that rapidly rehydrate and resume growth when water returns.

Capillary rehydration

Rapid uptake of water into dry plant tissues along cell walls via capillary action when water becomes available.

Paraphyllia

Hair-like structures on some moss stems that attract and store water from fog or dew to keep moss hydrated.

Spongin

Protein in natural sponges that makes them porous and highly absorbent; natural sponges can hold large amounts of water.

Natural vs. artificial sponge

Natural sponges are made from living sponge tissue containing spongin; artificial sponges mimic absorption and avoid harvesting wild sponges.

Phospholipid

Amphipathic molecule with a hydrophilic head and hydrophobic tail; forms lipid bilayers in cell membranes, enabling selective permeability.

Oxygen solubility in water

Oxygen dissolves sparingly in water; solubility decreases with higher temperature; hemoglobin in blood increases overall oxygen transport capacity.

Haemoglobin

Oxygen-binding protein in red blood cells that greatly increases the blood’s capacity to transport oxygen.