IB DP Biology - A1.1 Water Review

1. What type of bond holds the hydrogen and oxygen atoms together within a single water molecule?

•  Ionic bond

• Covalent bond

• Hydrogen bond

• Peptide bond

Answer explanation

Water molecules are held together by polar covalent bonds, where oxygen is more electronegative than hydrogen, creating a partial charge separation.

The ability of water molecules to form hydrogen bonds is due to:

• The symmetrical shape of the molecule

• The high molecular weight of water

• The partial positive and negative charges on hydrogen and oxygen

• The presence of free electrons on oxygen

Answer explanation

Water is polar, with oxygen having a partial negative charge (δ-) and hydrogen a partial positive charge (δ+), allowing hydrogen bonding.

What type of bond forms between separate water molecules?

• Covalent bond

•  Ionic bond

• Hydrogen bond

• Van der Waals interactions

Answer explanation

Hydrogen bonds occur between the oxygen of one molecule and the hydrogen of another, creating water’s unique properties.

1. Cohesion in water is primarily due to:

• Covalent bonds between molecules

• Hydrogen bonding between molecules

• Adhesion to other surfaces

• The presence of dissolved ions

Answer explanation

Water molecules stick together due to hydrogen bonding, leading to phenomena like surface tension and capillary action.

Which of the following best explains why water has a high surface tension?

• Water has low molecular weight

• Hydrogen bonding pulls molecules tightly at the surface

• Water has a high heat capacity

• Water molecules have weak intermolecular forces

Answer explanation

Water molecules at the surface experience stronger cohesive forces, creating resistance to external force (high surface tension).

Water is an excellent solvent because:

• It can dissolve all substances

• It forms hydrogen bonds with nonpolar molecules

• Its polarity allows it to dissolve ionic and polar substances

• It has low molecular mass

Answer explanation

Water dissolves polar and ionic substances due to the attraction between charges but does not dissolve nonpolar molecules like lipids.

Why does water have a high specific heat capacity?

• Water is a small molecule

• Hydrogen bonds absorb heat before breaking

• Water has a high molecular mass

• Water is nonpolar

Answer explanation

A lot of energy is needed to break hydrogen bonds, allowing water to resist temperature changes and maintain stable conditions.

Why is sweating an effective cooling mechanism in humans?

• It increases body heat production

• It releases excess carbon dioxide

• Water has a high latent heat of vaporization, allowing heat loss

• It reduces energy use in cells

Answer explanation

As sweat evaporates, it absorbs large amounts of heat due to water’s high latent heat of vaporization, cooling the body efficiently.

Tags

NGSS.HS-LS1-3

Why does ice float on water?

• Ice is denser than liquid water

• Ice contains more oxygen atoms

• Ice has a lower density than liquid water due to hydrogen bonding

• Ice has higher kinetic energy than water

Answer explanation

Hydrogen bonding in ice forms a lattice structure, increasing the space between molecules and reducing density, allowing ice to float.

What would happen if ice were denser than liquid water?

• Ice would float more easily

• Aquatic ecosystems would be unaffected

• Ice would sink, potentially freezing entire bodies of water

• Water would evaporate more slowly

Answer explanation

If ice were denser, it would sink, leading to the progressive freezing of water bodies, which could make aquatic life unsustainable.

Tags

NGSS.MS-PS1-4