IB Bio SL Topic A1.1 (Water)

What is the molecular structure of water?

Water (H₂O) contains two hydrogen atoms covalently bonded to one oxygen atom.

Why is water a polar molecule?

Oxygen has a stronger attraction for electrons, creating partial charges: O is δ− and H is δ+.

What is a hydrogen bond?

A weak attraction between the δ+ hydrogen of one water molecule and δ− oxygen of another.

Why can water form hydrogen bonds?

Water is polar, so its partial positive and negative charges attract neighboring molecules.

What is cohesion?

Attraction between molecules of the same substance.

Why does water have strong cohesion?

Hydrogen bonds cause water molecules to attract one another.

What is adhesion?

Attraction between molecules of different substances.

How does adhesion help plants?

Water molecules adhere to xylem walls, helping water move upward.

What is surface tension?

The resistance of a water surface to being broken or stretched.

Why does water have high surface tension?

Strong cohesion caused by hydrogen bonding holds surface molecules together.

What is specific heat capacity?

The energy needed to raise the temperature of a substance by 1°C.

Why does water have a high specific heat capacity?

Hydrogen bonds absorb much energy before water's temperature changes significantly.

Why is water's high specific heat capacity biologically important?

It helps organisms and aquatic environments resist rapid temperature changes.

Why does water have a relatively high boiling point?

Energy is needed to overcome the hydrogen bonds between water molecules.

Why is water a good solvent?

Its polarity allows it to dissolve many ionic and polar substances.

What types of substances dissolve well in water?

Ionic and polar substances dissolve well because they interact with water's partial charges.

Why is water useful for transport?

Dissolved substances can be transported in aqueous solutions such as blood and plant sap.

Why is water important as a medium for metabolic reactions?

Many biochemical reactions occur in aqueous solutions inside cells.

How does water participate in hydrolysis?

Water is added to break a covalent bond in a larger molecule.

Why is water important for living organisms?

Its properties support temperature regulation, transport, chemical reactions, and cellular processes.