IB Biology: Properties and Importance of Water

Comprehensive vocabulary flashcards covering the molecular structure, polarity, hydrogen bonding, cohesive, adhesive, solvent, thermal, and physical properties of water, transport mechanisms in living organisms, extraplanetary origins, and astrobiological significance based on IB Biology Topic A1.1 / 2.2.

Polar Covalent Bond

A chemical bond holding atoms together where shared electrons are pulled unequally due to differences in electronegativity, creating a slight positive charge ($\delta^+$) on one atom and a slight negative charge ($\delta^-$) on the other.

Hydrogen Bond

A transitory intermolecular attraction between a slightly positive hydrogen atom ($\delta^+$) of one polar molecule and a slightly negative region ($\delta^-$) of another polar molecule.

Cohesion

The property of water molecules sticking to one another as a result of dipolarity and the formation of numerous intermolecular hydrogen bonds.

Surface Tension

The property of a liquid surface caused by cohesive hydrogen bonding that resists external force, causing the surface to behave like a stretched elastic membrane.

Adhesion

The attraction and bonding of water molecules to other polar or charged (hydrophilic) molecules via hydrogen bonding.

Capillary Action

The movement of water through a narrow space driven by a combination of adhesive forces bonding water to a polar surface and cohesive forces holding water molecules together.

Capillarity

The rate at which water is pulled upward from the water table into pore spaces in soil by capillary action.

Hydrophilic

A term meaning 'water-loving', describing polar molecules (e.g., glucose) and charged ions (e.g., $\text{Na}^+$, $\text{Cl}^-$) that are chemically attracted to water and dissolve in or adhere to it.

Hydrophobic

A term meaning 'water-fearing', describing nonpolar, uncharged substances (such as lipids, fats, and oils) that do not dissolve in water and clump together when exposed to it.

Solvation

The process in which solvent molecules interact with a dissolved solute by forming electrostatic attractions or hydrogen bonds, creating a hydration shell around the solute particles.

Lipoprotein Complex

A spherical transport particle consisting of an outer monolayer of phospholipids and embedded proteins surrounding a hydrophobic inner core of fats and cholesterol esters, allowing insoluble lipids to travel in blood plasma.

Specific Heat Capacity

The quantity of heat needed to raise the temperature of a unit mass of a substance by $1\,^\circ\text{C}$; water has a high specific heat capacity of $4.2\,\text{J\,g}^{-1}\,{^\circ\text{C}}^{-1}$ ($4,183\,\text{J\,kg}^{-1}\,\text{K}^{-1}$) due to its extensive hydrogen bonding.

Latent Heat of Vaporisation

The amount of energy required to change a liquid into a vapour; water's high value ($2257\,\text{J\,g}^{-1}$) allows sweat evaporation to effectively remove heat energy from skin and blood vessels.

Methane ($\text{CH}_4$)

A nonpolar hydrocarbon produced as a waste product of anaerobic respiration in methanogenic prokaryotes, characterized by a density of $0.46\,\text{g\,cm}^{-3}$, specific heat capacity of $2.2\,\text{J\,g}^{-1}\,{^\circ\text{C}}^{-1}$, and a boiling point of $-160\,^\circ\text{C}$.

Hemoglobin

An iron-containing protein in red blood cells with $4$ binding sites for oxygen that carries the majority of oxygen in the blood, overcoming oxygen's low solubility in blood plasma at body temperature ($37\,^\circ\text{C}$).

Cytosol

The liquid component of the cytoplasm comprising roughly $80\%$ water, dissolved salts, sugars, amino acids, and enzymes, providing the aqueous medium for cellular metabolism.

Buoyancy

An upward buoyant force exerted on an object immersed in a fluid; if the object's density is lower than the fluid's density, the buoyant force overcomes gravity and the object floats.

Swim Bladder

An internal organ in bony fish that adjusts the volume of gas inside to alter body density, enabling control over vertical positioning and buoyancy in water.

Viscosity

A measure of a fluid's resistance to flow caused by internal friction between molecules; water's hydrogen bonds increase its viscosity relative to air or nonpolar organic solvents.

Thermal Conductivity

The measure of a material's ability to transfer heat across a temperature gradient; water has a significantly higher thermal conductivity than air, conducting heat away from organisms rapidly.

Ringed Seal (Pusa hispida)

An Arctic marine mammal that uses a thick blubber layer for insulation against water's high thermal conductivity and possesses a streamlined shape to swim efficiently through viscous water.

Black-throated Loon (Gavia arctica)

An Arctic bird that utilizes water buoyancy to float, experiences low thermal conductivity when flying in air, and features hollow bones with internal struts to reduce overall body density.

Deuterium to Hydrogen (D/H) Ratio

An isotopic ratio comparing heavy hydrogen (deuterium) to normal hydrogen in water, used to show that Earth's oceans and outer-belt asteroids share matching values and a common origin.

Extraplanetary Origin of Water

The leading hypothesis stating that water arrived on Earth around $4.5$ billion years ago via impacts from water-rich celestial objects, primarily asteroids from the outer asteroid belt between Mars and Jupiter.

Goldilocks Zone

The habitable orbital region surrounding a star where ambient temperatures allow water to exist continuously in liquid form on a planet's surface.

Astrobiology

The branch of science concerned with studying the origins, distribution, and future possibility of life in the universe, using the presence of liquid water as a primary indicator.

Hydrolysis Reaction

A metabolic reaction where a water molecule is consumed as a reactant to split a larger compound into smaller molecular subunits.

Condensation Reaction

A metabolic reaction in which two smaller molecules combine to synthesize a larger molecule, releasing a water molecule as a product.