AP Biology / Chemistry of Life
Lesson
Water as a working solvent
Hydrogen bonds are individually weak and collectively stubborn.
Learning goals
- Explain cohesion, adhesion, and high specific heat with hydrogen bonding.
- Connect water’s polarity to dissolving ions and many biological molecules.
Explanation
A water molecule has a slightly negative oxygen and slightly positive hydrogens. Neighboring molecules tug on one another through hydrogen bonds. That tug helps water stay liquid over a useful temperature range and resist quick heating—useful around enzymes that fail when they cook.
Polar and charged substances mix with water. Nonpolar chains do not, which is why oil beads and why membrane lipids arrange themselves. When you explain a property, finish the sentence in a living system: sweating, transport in plants, or the solvent inside cytoplasm.
Key terms
- Hydrogen bond. An attraction between a slightly positive hydrogen and a nearby electronegative atom, common among water molecules.
- Polarity. Uneven charge distribution within a molecule that affects how it interacts with others.
Common mistakes
- Calling a hydrogen bond as strong as a covalent bond inside a water molecule.
- Listing water properties without a biological consequence.
Practice
Original Marlow Works items. Check the answer explanation after you try.
A cell’s surface-area-to-volume ratio is important because it affects:
Original Marlow Works item — not a College Board question.
Take your time—this is practice, not a test.
Answer explanation
Why can water climb a narrow xylem tube more readily than a nonpolar liquid would?
Answer. Adhesion to the tube walls and cohesion among water molecules let a continuous column form.
Polarity makes both the water–water and water–wall attractions possible.
Related resources
External links with reuse status. Marlow Works is independent and does not copy restricted exam or textbook material.
Official / link only
AP Biology course page
Official eight-unit framework, science practices, and lab resources.
College Board · All rights reserved · accessed 2026-10-01
Open sourceReference only — do not copy
OpenStax Biology 2e
Biology reference with commercial-use restrictions on the current publisher page.
OpenStax · CC BY-NC-SA 4.0 with additional restrictions · accessed 2026-10-01
Link only unless permission is obtained.
Open source