AP Biology - Unit 1.1: Structure of Water and Hydrogen Bonding

What is the chemical structure of water?

Water (H₂O) consists of two hydrogen atoms covalently bonded to one oxygen atom. The molecule has a polar covalent bond, with oxygen being partially negative and hydrogen being partially positive.

How does the chemical structure of water result in polarity?

Oxygen is more electronegative than hydrogen, causing it to attract electrons more strongly, which leads to the polarity of the molecule (oxygen is partially negative, hydrogen is partially positive).

What is hydrogen bonding in water molecules?

Hydrogen bonding is a weak interaction that occurs when the negative pole of an oxygen atom in one water molecule is attracted to the positive pole of a hydrogen atom in another water molecule.

What is cohesion in water?

Cohesion is when water molecules are attracted to each other due to hydrogen bonds, allowing them to stick together (e.g., surface tension).

What is adhesion in water?

Adhesion is when water molecules are attracted to different molecules or surfaces (e.g., water sticking to the sides of a container or climbing up plant roots).

What are the properties of water due to cohesion and adhesion?

Properties include high heat capacity, high heat of vaporization, surface tension, and capillary action. These allow water to maintain stable temperatures, support aquatic life, and move through narrow spaces like plant roots.

What causes water’s high surface tension?

Water molecules experience cohesive forces that pull them inward or towards each other, creating a “skin” on the surface. This allows small objects like water striders to float.

How does cohesion contribute to ice floating on water?

Cohesion causes water molecules to stick together, making liquid water denser than ice. As a result, ice (which is less dense) floats on water.

How does adhesion contribute to water’s high solvency ability?

Adhesion allows water to surround and dissolve various substances, such as salts and nutrients, making it an excellent solvent.

What is capillary action and how is it driven by cohesion and adhesion?

Capillary action is the movement of water through narrow spaces. Cohesion helps water molecules stick together, while adhesion helps them stick to the walls of the narrow space, allowing water to rise (e.g., in plant roots or paper towels).

Why is water important for living systems?

Water’s properties (cohesion, adhesion, high heat capacity, high heat of vaporization) help maintain stable environments for living organisms, support nutrient transport, and regulate temperature in biological systems.

Hydrophilic

A charged or polar substance that interacts with and dissolves in water.

Hydrophobic

A non - polar substance that separates from water rather than being dissolved. Such as oil and fats.

What is a meniscus in the context of water in a glass container?

A meniscus is the curve seen at the surface of a liquid in a container, caused by the attraction between the water molecules and the glass surface. Water is more attracted to the glass (adhesion) than to itself (cohesion), resulting in its curved shape.

What is cohesion in water, and how does it relate to hydrogen bonding?

Cohesion refers to the attraction between molecules of the same substance. In water, hydrogen bonds between water molecules create strong cohesive forces, causing water molecules to stick to each other.

What phenomenon results from water’s cohesive properties, and how is it related to hydrogen bonding?

Surface tension is the result of cohesive forces in water. The hydrogen bonds between water molecules cause them to resist rupture as they are densely packed and are more attracted to themselves than their surface such as air, creating a “skin” on the surface that can support small objects.

How does surface tension allow water to form spherical droplets and support small objects?

Due to hydrogen bonding, water molecules at the surface form stronger bonds with each other because they are exposed to air on one side. This creates surface tension, which enables water droplets to form and support objects like a needle on the surface.

What is adhesion in water, and how is it related to hydrogen bonding?

Adhesion is the attraction between water molecules and different substances. Hydrogen bonds form between water molecules and other polar substances, such as glass, allowing water to stick to surfaces.

How does adhesion contribute to capillary action in water?

Adhesion allows water molecules to stick to the walls of narrow polar material tubes (e.g., capillary tubes or glass). This, along with cohesion between water molecules, causes water to move upwards against gravity, a process called capillary action.

Why is the meniscus formed when water is in a tube, and what causes its shape?

The meniscus forms due to the adhesive force between water and the walls of the tube. Water molecules are more attracted to the glass than to each other, causing the water to rise slightly at the edges of the tube, forming a curved surface.

How do cohesive and adhesive forces play a role in biological processes?

Cohesion and adhesion are crucial in processes like the movement of water through plants (e.g., from roots to leaves) and in the drainage of tears from the tear ducts. These forces enable water to travel and support various biological functions.

How does the water strider insect use surface tension to stay afloat?

The water strider relies on surface tension, created by cohesion between water molecules, to stay afloat on the water’s surface without sinking.

Surface