C2.2 Water

This section focuses on the unique properties of water and its crucial role in biological systems. The polarity of water molecules and their ability to form hydrogen bonds are explained in detail.

Vocabulary:

• Hydrophilic: polar molecules that dissolve in water
• Hydrophobic: non-polar molecules that repel water and are insoluble

A required diagram illustrating the structure of a water molecule and its hydrogen bonding is provided, helping students visualize these important concepts.

The properties of water are discussed in depth, including:

1. Cohesion: The ability of water molecules to stick to each other, creating surface tension.
2. Adhesion: Water molecules' ability to stick to other polar compounds.
3. Thermal properties: Water's role as a coolant in regulating temperature.
4. Solvent properties: Water's ability to dissolve polar compounds.

Example: Cohesion allows water to be pulled up from roots through the xylem in plants, demonstrating the importance of water's properties in biological processes.

The section also compares water to methane, highlighting the differences in polarity and latent heat of vaporization. This comparison helps students understand why water's properties are so unique and important for life.

C2.3 Carbohydrates and Lipids

This section provides a comprehensive overview of carbohydrates and lipids, two major classes of biomolecules. The discussion begins with carbohydrates, explaining their classification into monosaccharides, disaccharides, and polysaccharides.

Definition: Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with a 2:1 ratio of hydrogen to oxygen.

The section includes a detailed table listing various carbohydrates, their monomers, and their biological uses. This information is crucial for IB Biology HL students to understand the diversity and functions of carbohydrates in living systems.

Example: Sucrose, a disaccharide composed of glucose and fructose, is used to transport energy from leaves to storage organs in plants.

Polysaccharides are given special attention, with a focus on starch, glycogen, and cellulose. The properties of these complex carbohydrates are discussed, including their compact nature, insolubility, and ease of enzymatic hydrolysis.

Highlight: The structural differences between alpha and beta glucose are crucial for understanding the diverse functions of polysaccharides in nature.

The section begins to touch on the industrial applications of starch, setting the stage for a broader discussion of the practical uses of carbohydrates in various fields.

This detailed exploration of carbohydrates provides IB Biology HL students with a solid foundation for understanding more complex biochemical processes and the role of these molecules in living organisms.