Biology notes 3

Vocabulary flashcards covering the key water properties and acid–base concepts from the lecture notes.

Water (biological medium)

The Earth’s biological medium; organisms require it; cells are about 70–95% water; its abundance makes Earth habitable.

Polarity

A property of a molecule where opposite ends have partial charges, enabling hydrogen bonding (as in water).

Hydrogen bond

A weak attraction between a hydrogen atom on one molecule and an electronegative atom (like oxygen) on another, crucial for water’s properties.

Cohesion

Attraction between water molecules due to hydrogen bonding; helps transport water against gravity in plants.

Adhesion

Attraction between water and other substances (e.g., water and plant cell walls).

Moderation of temperature

Water’s ability to absorb heat from warm surroundings and release it to cooler surroundings, with only small temperature changes.

High specific heat

Water’s capacity to resist temperature change; due to hydrogen bonding; heat is absorbed when bonds break and released when they form.

Evaporative cooling

Cooling that occurs when a liquid evaporates, lowering the remaining surface temperature; helps stabilize temperatures in organisms and bodies of water.

Expansion upon freezing

Ice is less dense than liquid water because its hydrogen bonds are more ordered, causing ice to float.

Solvent

The dissolving agent in a solution; water is a versatile solvent due to its polarity.

Solute

The substance dissolved in a solvent.

Aqueous solution

A solution in which water is the solvent.

Hydration shell

A sphere of water molecules arranged around dissolved ions in solution.

Dissolve

To break up and distribute a solute uniformly within a solvent, forming a solution.

Hydrophilic

Water-loving substances that readily dissolve in water (ionic or polar bonds).

Hydrophobic

Water-fearing substances that do not readily dissolve in water (nonpolar).

Amphipathic

Molecules that have both polar (hydrophilic) and nonpolar (hydrophobic) regions.

Acid

A substance that increases the hydrogen ion (H+) concentration in a solution.

Base

A substance that reduces the hydrogen ion (H+) concentration, increasing pH.

pH

A scale measuring how acidic or basic a solution is; each unit represents a tenfold change in H+ concentration; neutral is 7.

Hydronium ion (H3O+)

A protonated water molecule; H+ in aqueous solutions is often represented as H3O+.

Hydroxide ion (OH−)

The negatively charged ion formed when water loses a proton; base component.

Neutral solution

A solution with [H+] and [OH−] balanced (pH ≈ 7).