AP bio-properties of water

water is polar

hydrogen and oxygen do not share electrons equally; covalent bond; positive electronegativity in H, negative electronegativity in O

water forms hydrogen bonds with other water

positively charged hydrogens bond with negatively charged oxygen; each water molecule connects to several others, leading to many other properties of water

surface tension

water’s ability to resist an external force, acting like a stretched elastic skin caused by strong cohesive H-bonds between its polar molecules

cohesion

the sticking together of particles of the same substance: water molecules stick to each other because of H-bonds, allows surface tension

high heat of vaporization

a large amount of energy is required to convert a liquid to a gas at a constant temperature: allows organisms to regulate their body temperature through sweating

high heat capacity

molecules held together by strong H-bonds, requires a large amount of energy: allows for stable temperatures in large bodies of water

solvent

capable of dissolving another substance to form a homogeneous mixture called a solution: allows polar and charged molecules to dissolve and interact freely within cells and the body

low density as a solid

H-bonds force molecules into a spread out structure, causing it to float: floating ice layer acts as an insulator in bodies of water, protecting aquatic life under the surface

adhesion

water molecules stick to other dissimilar substances do to H-bonding and the water molecule’s polar nature: enables water transport in plants through xylem against gravity

polar

electrons are not shared equally

nonpolar

electrons are shared equally

water potential

Ψ = Ψp + Ψs; Water moves from higher water potential (less negative) to lower water potential (more negative)

solute potential Ψs

Always negative (or zero for pure water); Decreases (becomes more negative) as solute concentration increases

Formula: Ψs = -iCRT (i=ionization, C=molarity, R=constant, T=temp in Kelvin).

pressure potential Ψp

Physical pressure on a solution; Zero in open containers (like a beaker in lab); Positive in turgid plant cells (due to cell wall pushing back).