Water and Hydrogen Bonding in Living Systems
Hydrogen bonds between water molecules give water its cohesion, its high heat capacity and its behaviour as a solvent. Every one of those properties traces back to the same charge separation across the molecule.
What a learner can do afterwards
- Explains cohesion and surface tension from bonds between neighbouring molecules rather than from water being sticky.
- Links the high specific heat capacity to what hydrogen bonds do when heat is added.
- Predicts which solutes dissolve readily in water and says what about the molecule decides it.
1 · Read
You saw water rush into red blood cells until they burst and into plant cells until walls held them firm. A water molecule is polar. Oxygen pulls shared electrons toward itself, leaving the oxygen end slightly negative and the hydrogen ends slightly positive. The hydrogen side of one molecule is drawn to the oxygen side of its neighbour, and that link is called a hydrogen bond. Each bond is weak, but together they act strong.
Those links explain everyday sights. Drops bead up, insects dent the surface without sinking, and water climbs thin plant stems as each molecule drags the next along. None of this happens because water is sticky like glue. It happens because neighbours keep holding hands, which is called cohesion.
Heating water means shaking that network apart, which soaks up a lot of energy. So water warms slowly and cools slowly, and that high heat capacity steadies the temperature inside living things.
Let polarity decide what dissolves. The charged ends of water surround ions and polar molecules and tug them apart, which is why salt vanishes into water. Molecules without charged regions get no such grip, so fats and oils bead up instead of mixing.
One polar molecule builds a network of bonds, and that network explains clinging, slow warming and dissolving.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.