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🐇Honors Biology

🐇honors biology review

2.2 Water and Its Properties

3 min readLast Updated on August 7, 2024

Water is the foundation of life on Earth. Its unique molecular structure gives it properties essential for biological processes. From its polarity to its ability to form hydrogen bonds, water's characteristics make it indispensable for living organisms.

Understanding water's properties is key to grasping biochemistry. Its role as a solvent, its thermal properties, and its cohesive nature all contribute to how molecules interact within cells and how life functions at the molecular level.

Molecular Properties of Water

Polarity and Hydrogen Bonding

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  • Water is a polar molecule due to the uneven distribution of electrons between the oxygen and hydrogen atoms
    • The oxygen atom has a slight negative charge while the hydrogen atoms have a slight positive charge
  • The polarity of water allows it to form hydrogen bonds with other water molecules
    • Hydrogen bonds are weak electrostatic attractions between the positive hydrogen of one molecule and the negative oxygen of another
  • Hydrogen bonding gives water many of its unique properties (cohesion, adhesion, surface tension)

Cohesion, Adhesion, and Surface Tension

  • Cohesion refers to the attraction between water molecules due to hydrogen bonding
    • Cohesion allows water to maintain its liquid state and resist separation
    • Cohesion contributes to water's high surface tension
  • Adhesion is the attraction between water molecules and other substances
    • Water molecules can adhere to the walls of a container, allowing it to form menisci
    • Adhesion, along with cohesion, enables water to move up narrow tubes (capillary action) which is crucial for water transport in plants
  • Surface tension is the tendency of water molecules to be attracted to each other at the surface, creating a "skin-like" layer
    • Surface tension allows some insects (water striders) to walk on water without breaking the surface
    • Surface tension also enables the formation of water droplets and bubbles

Water as a Solvent

Solvent Properties

  • Water is known as the "universal solvent" due to its ability to dissolve a wide variety of substances
    • As a solvent, water can dissolve ionic compounds (salts), polar molecules (sugars), and gases (oxygen)
  • The polarity of water allows it to interact with and surround solute particles, effectively dissolving them
    • Water molecules orient themselves with the positive ends towards negative ions and the negative ends towards positive ions

Hydrophilic and Hydrophobic Substances

  • Hydrophilic substances are attracted to water and readily dissolve in it
    • Hydrophilic substances (sugar, salt) have polar or charged regions that interact favorably with water molecules
    • Many biological molecules (proteins, DNA) have hydrophilic regions that allow them to interact with the aqueous environment of the cell
  • Hydrophobic substances are repelled by water and do not dissolve easily
    • Hydrophobic substances (oils, fats) are typically nonpolar and do not interact favorably with water molecules
    • In living organisms, hydrophobic molecules (lipids) often form structures like cell membranes that separate aqueous compartments

Thermal Properties of Water

High Specific Heat Capacity

  • Specific heat is the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius
    • Water has a high specific heat capacity of 4.18 J/g°C, meaning it requires a lot of energy to change its temperature
  • The high specific heat of water is due to the extensive hydrogen bonding between molecules
    • When water is heated, much of the energy is used to break hydrogen bonds before the molecules can move faster and the temperature increases
  • Water's high specific heat allows it to absorb and release large amounts of heat energy without much change in temperature
    • This property helps regulate the temperature in living organisms and the environment (oceans, lakes)
    • Water's high specific heat also makes it an excellent coolant in industrial applications and in the regulation of body temperature through sweating

Key Terms to Review (17)

Metabolism: Metabolism refers to the set of life-sustaining chemical reactions that occur within living organisms to convert food into energy. This process includes both catabolism, which breaks down molecules to release energy, and anabolism, which uses energy to build cellular components. Understanding metabolism is crucial as it links the characteristics of life, the role of water in biochemical reactions, and the energy transformations facilitated by ATP.
Homeostasis: Homeostasis is the process by which living organisms maintain a stable internal environment despite changes in external conditions. This dynamic equilibrium is crucial for survival, enabling organisms to regulate factors like temperature, pH, and nutrient concentrations, which directly influence cellular function and overall health.
Transpiration: Transpiration is the process by which plants absorb water from the soil, transport it through their vascular systems, and release it as water vapor into the atmosphere through small openings called stomata. This process not only helps in maintaining plant health and temperature but also plays a critical role in the water cycle and climate regulation.
Water Cycle: The water cycle is the continuous process through which water circulates between the Earth's surface and the atmosphere. This cycle involves various stages, including evaporation, condensation, precipitation, and infiltration, which play a critical role in maintaining the balance of ecosystems and influencing climate patterns. Understanding the water cycle helps explain how water moves and transforms in different states, impacting both terrestrial and aquatic environments.
Density of Ice: The density of ice refers to the mass per unit volume of ice, which is approximately 0.92 grams per cubic centimeter (g/cm³). This unique property means that ice is less dense than liquid water, allowing it to float. The unusual behavior of ice is significant as it influences aquatic ecosystems and climate patterns, impacting everything from weather phenomena to the survival of organisms in cold environments.
Hydrophilic: Hydrophilic refers to the property of a substance that has a strong affinity for water, allowing it to interact or dissolve easily in aqueous environments. This characteristic is crucial in biological systems, influencing how molecules behave in water and their role in cellular structures and functions. Hydrophilic molecules often contain polar groups that enable them to form hydrogen bonds with water, leading to significant implications for processes like solvation and membrane dynamics.
Heat of vaporization: The heat of vaporization is the amount of energy required to convert a unit mass of a substance from liquid to gas at constant temperature and pressure. This property is particularly important for water, as it plays a crucial role in regulating temperature in biological systems and affects climate patterns. Water's high heat of vaporization means that it can absorb significant amounts of heat without a large increase in temperature, making it essential for maintaining homeostasis in organisms and influencing environmental conditions.
High Specific Heat: High specific heat refers to the ability of a substance, such as water, to absorb and retain a significant amount of heat energy without experiencing a substantial increase in temperature. This property is crucial for regulating temperature in the environment, making it vital for maintaining homeostasis in living organisms and stabilizing climate patterns on Earth.
Hydrophobic: Hydrophobic refers to the property of molecules that do not interact well with water, making them resistant to being dissolved in aqueous environments. This characteristic is largely due to the nonpolar nature of hydrophobic molecules, which repels water molecules and is crucial in understanding various biological processes, including the behavior of cell membranes and protein folding.
Capillary Action: Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces, such as gravity. This phenomenon occurs due to the combination of adhesive forces between the liquid and the surfaces of solid materials, and cohesive forces within the liquid itself. It plays a crucial role in various biological and physical processes, particularly in water transport systems within plants and the unique properties of water.
Universal Solvent: The universal solvent refers to water, which is known for its ability to dissolve a wide range of substances due to its polar nature and hydrogen bonding. This characteristic allows water to facilitate chemical reactions, transport nutrients, and play a crucial role in biological processes. The unique properties of water, including its polarity and high dielectric constant, enable it to interact effectively with various solutes, making it essential for life on Earth.
Hydrogen Bond: A hydrogen bond is a weak attraction that occurs between a hydrogen atom covalently bonded to a highly electronegative atom, such as oxygen or nitrogen, and another electronegative atom. This type of bond is crucial in stabilizing the structures of larger biological molecules, especially in water, which has unique properties essential for life. The presence of hydrogen bonds affects the boiling point, melting point, and solubility of substances, making them fundamental in various chemical and biological processes.
Adhesion: Adhesion refers to the tendency of different types of molecules to stick together. This property is crucial for many biological processes, especially because it allows for interactions between water molecules and other substances, playing a key role in various physiological functions. The ability of water to adhere to surfaces is significant in processes like nutrient transport in plants and in the overall movement of water through different ecosystems.
Cohesion: Cohesion is the property of water molecules that allows them to be attracted to one another due to hydrogen bonding. This attraction results in water molecules sticking together, which is crucial for various biological processes. The high level of cohesion in water contributes to its unique characteristics, such as surface tension and the ability to form drops, which play essential roles in the movement of water in living organisms and ecosystems.
Solvent: A solvent is a substance that dissolves a solute, resulting in a solution. In biological systems, water is the most common solvent and plays a crucial role in various biochemical processes, allowing substances to interact and react effectively within living organisms.
Surface Tension: Surface tension is the cohesive force that causes liquid surfaces to shrink into the smallest possible surface area. This phenomenon occurs due to the attraction between liquid molecules, which creates a 'skin-like' effect at the surface. Surface tension is a critical property of water, enabling it to support small objects and organisms, contributing to various biological processes, and playing a key role in capillary action.
Polarity: Polarity refers to the distribution of electrical charge around atoms and molecules, which affects their interactions and behaviors. Molecules can be polar or nonpolar depending on the arrangement of atoms and the electronegativity differences between them. This concept is crucial for understanding how substances interact with each other, particularly in biological systems.