AP Biology: Chemical Context of Life and Properties of Water

Vocabulary flashcards covering chemical structure, polarity, electronegativity, pH, and the physical properties of water in biology.

Polar Molecule

A substance with an uneven distribution of electronegativity across its structure, causing one side to have a different charge than another side.

Universal Solvent

A property of water referring to its ability to dissolve most other polar substances due to its own polar molecular nature.

Ammonia ($\text{NH}_3$)

A polar, trigonal pyramidal molecule containing $8$ valence electrons, where nitrogen has an electronegativity of $3.0$ and hydrogen has $2.1$.

Phosphine ($\text{PH}_3$)

A non-polar, trigonal pyramidal molecule where phosphorus and hydrogen both have an electronegativity of $2.1$, resulting in no charge difference.

Sulfur Trioxide ($\text{SO}_3$)

A non-polar, trigonal planar molecule exhibiting resonance, where equal polar bonds between sulfur ($2.5$) and oxygen ($3.5$) cancel out.

Methane ($\text{CH}_4$)

A non-polar, tetrahedral molecule consisting of $8$ valence electrons with carbon ($2.5$) and hydrogen ($2.1$).

Density of Ice vs. Liquid Water

Water freezes at 0^\text{ }^\text{o}\text{C} (32^\text{ }^\text{o}\text{F}), causing hydrogen bonds between molecules to lengthen by $10\%$. This creates more space between molecules, making solid ice less dense than liquid water.

Spring Overturn

The seasonal process where melting surface ice turns into liquid water that reaches its maximum density at 4^\text{ }^\text{o}\text{C} and sinks, cycling oxygen ($\text{O}_2$) and nutrients down while pushing bottom water upward.

Capillary Action

The ability of water to move upward against gravity inside a thin tube without using energy, driven by the combined effects of adhesion and cohesion.

Adhesion

The tendency of water molecules to stick to a different substance, such as partial positive hydrogen atoms clinging to negatively charged xylem walls.

Cohesion

The property of water molecules to stick to other water molecules.

Xylem

Straw-like vessel tubes in plants that transport water from roots up to leaves.

Stomata

Tiny openings located on leaves where water evaporates into the atmosphere.

Transpiration

The process of water evaporating at the leaves through stomata, generating the strongest pulling force for water movement in plants via adhesion and cohesion.

Specific Heat of Water

The amount of energy required to raise $1\,\text{g}$ of water by 1^\text{ }^\text{o}\text{C}, which equals 1\,\text{cal/g}^\text{ }^\text{o}\text{C}, a high value relative to other substances.

Evaporative Cooling

A mechanism where high-energy, hot molecules leave the body as sweat, lowering skin temperature and cooling the blood returning to the heart.

Surface Tension

The tension created at the water surface due to cohesive forces pulling water molecules downward, as non-polar air exerts no upward attraction.

pH Concentration Difference

A comparison of hydrogen ion concentration $[\text{H}^+]$, where a solution of pH $5$ ($10^{-5}\text{ M}$) is $100{,}000$ times more acidic than a solution of pH $10$ ($10^{-10}\text{ M}$).