1.1 - Properties of Water Presentation

1.1 Structure of Water and Hydrogen Bonding

Learning Objective

• SYI 1.A: Explaining how properties of water, resulting from its polarity and hydrogen bonding, affect its biological function.

Discussion Prompt

• Consider the role of water in maintaining life.

2.0 How Does Water Support Life?

• Chemical Reactions: Water is vital for numerous chemical reactions essential for homeostasis.

• Transport of Materials:

  • Blood in Animals: Transports oxygen and nutrients.

  • Sap in Plants: Carries nutrients and water upwards from the roots.

3.0 Chemical Properties of Water

Unique Suitability for Supporting Life

• Polarity of Water:

  • Water is a polar molecule with partial positive and negative charges.

  • This allows water to form hydrogen bonds with itself and with other polar or charged molecules.

• Effects of Polarity:

  • Cohesion and Adhesion: Water molecules stick together and adhere to other surfaces.

  • Surface Tension: Water's cohesive property creates surface tension, allowing some organisms to float.

  • Temperature Resistance: Water resists temperature changes due to strong hydrogen bonds.

  • Excellent Solvent: Water can dissolve a variety of substances.

4.0 Cohesion vs. Adhesion

Adhesion

• Water molecules can hydrogen bond with other polar/charged molecules.

• This causes water to adhere to surfaces, forming droplets.

Cohesion

• Water exhibits cohesion, resulting in surface tension.

• Capillary action: Water can move up through narrow spaces due to cohesion and adhesion.

5.0 Surface Tension

• Mechanism: Cohesion among surface water molecules results in stronger hydrogen bonds.

• Effects:

  • Defined surface prevents rupture from light objects.

  • Example: Water skater bugs able to walk on water.

6.0 Capillary Action

• Process: Water adheres to polar surfaces and climbs up tubes without separating due to cohesion.

• Biological Importance:

  • Plants transport water from roots to leaves utilizing capillary action for photosynthesis.

7.0 Water Resists Temperature Changes

• Hydrogen Bonds: Individually weak but collectively strong, causing water to have a high specific heat capacity.

• Importance: Helps organisms maintain a constant internal temperature, crucial for homeostasis.

8.0 Solvency of Water

• Excellent Solvent: Water’s polarity allows it to dissolve ionic compounds (e.g., salt) and form hydration shells around polar molecules (e.g., sugar).

• Biological Significance:

  • Essential for cellular respiration and proper physiological functions.

9.0 Main Concepts

• Polarity and Hydrogen Bonding: Critical for supporting living systems through:

  • Cohesion and Adhesion: Enabling capillary action and surface tension.

  • Solvency: Ability to dissolve polar compounds.

  • Temperature Regulation: High energy required to break hydrogen bonds, contributing to constant internal temperature.

10.0 Practice Free Response Question

• AP Biology (2009 Form B):

  1. Discuss three properties of water.

  2. Explain the role of water in:

     • Metabolic processes in cells.

     • Moderating temperature within organisms and environments.

     • Movement of water in plants from roots to leaves.

Possible Free Response Questions (FRQs) for Water Structure and Function:

1. Discuss the importance of water's polarity in biological systems.

   • In your answer, include how polarity affects cohesion and adhesion, and provide examples of its biological significance.

2. Explain the mechanism and significance of capillary action in plants.

   • Describe how cohesion and adhesion work together in this process, and discuss its role in nutrient transport.

3. Analyze the impact of water's high specific heat on temperature regulation in living organisms.

   • Include how this property influences homeostasis in both animals and plants.

4. Describe the chemical properties of water that make it an excellent solvent.

   • Discuss how water's ability to form hydration shells contributes to cellular processes.

5. Compare and contrast cohesion and adhesion in the context of water's biological functions.

   • Provide examples of how each property is utilized within ecosystems or specific organisms.

Some key terms you should know for a test on the structure and function of water include:

1. Polarity: Refers to the distribution of electrical charge over the atoms joined by the bond, leading to partial charges that allow water to form hydrogen bonds.

2. Hydrogen Bonding: The weak attraction between a hydrogen atom of one water molecule and the oxygen atom of another, essential for many properties of water.

3. Cohesion: The ability of water molecules to stick to each other, responsible for surface tension and capillary action.

4. Adhesion: The tendency of water to stick to other substances, which helps in processes like nutrient transport in plants.

5. Surface Tension: The elastic-like force existing at the surface of water due to cohesive forces, enabling some organisms to walk on water.

6. Capillary Action: The ability of water to flow in narrow spaces without external forces, crucial for water transport in plants.

7. Specific Heat Capacity: The amount of energy required to change the temperature of water, which helps in temperature regulation for organisms.

8. Solvent: Water's property as an excellent solvent for ionic and polar substances, vital for biological processes like cellular respiration.