Water's Role in Living Systems
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Questions and Answers

What is the significance of hydrogen bonds in water?

  • They prevent water from forming crystalline structures.
  • They decrease water's ability to dissolve polar biomolecules.
  • They allow water to exist as a gas at higher temperatures.
  • They contribute to the cohesive forces that keep water liquid at room temperature. (correct)

    • Which statement regarding the ionization of water is accurate?

  • The ionization of water is only significant at high temperatures.
  • Water doesn't ionize and remains neutral at all times.
  • Water ionizes to form carbonic acid and bicarbonate in biological systems.
  • Water can ionize into hydrogen ions (H⁺) and hydroxide ions (OH⁻). (correct)

    • How do weak acids and bases behave in aqueous solutions?

  • They completely dissociate and do not act as buffers.
  • They increase the concentration of OH⁻ ions in a solution.
  • They can help maintain pH levels by neutralizing strong acids and bases. (correct)
  • They do not influence the properties of other solutes present.

    • What role does water play in the self-assembly of biomolecules?

    <p>Water provides a medium that influences molecular interactions through hydrogen bonding. (A)</p> Signup and view all the answers

    Why do polar biomolecules dissolve readily in water?

    <p>They replace water-water interactions with energetically favorable water-solute interactions. (B)</p> Signup and view all the answers

    What percentage of the weight of most organisms is made up of water?

    <p>70% or more (C)</p> Signup and view all the answers

    What happens to the molecular structure of water when it freezes?

    <p>Water forms hydrogen bonds that lead to extreme ordering typical of crystalline ice. (D)</p> Signup and view all the answers

    What aspect of water profoundly influences the properties of cellular components like proteins and nucleic acids?

    <p>The solvent properties of water, including hydrogen bonding. (B)</p> Signup and view all the answers

    What is the reason for water's unusual properties, such as its high melting point and boiling point?

    <p>Strong hydrogen bonds between adjacent water molecules (D)</p> Signup and view all the answers

    Why do nonpolar molecules tend to be poorly soluble in water?

    <p>They disrupt water-water interactions and can't form water-solute interactions (A)</p> Signup and view all the answers

    What is the bond angle in a water molecule?

    <p>104.5 degrees (B)</p> Signup and view all the answers

    What is the bond dissociation energy for hydrogen bonds in liquid water?

    <p>23 kJ/mol (C)</p> Signup and view all the answers

    What effect does the electronegativity of oxygen have on the water molecule?

    <p>It results in unequal sharing of electrons and formation of dipoles (C)</p> Signup and view all the answers

    How do hydrogen bonds in liquid water compare to covalent bonds?

    <p>Hydrogen bonds are relatively weak and longer than covalent bonds (B)</p> Signup and view all the answers

    What defines the hydrophobic effect in aqueous solutions?

    <p>The tendency of nonpolar molecules to cluster together (A)</p> Signup and view all the answers

    Which property of water is primarily affected by its hydrogen bonding?

    <p>Its specific heat capacity (D)</p> Signup and view all the answers

    What type of interactions contribute to the three-dimensional structures of biomolecules?

    <p>Hydrogen bonds, ionic, hydrophobic, and van der Waals interactions (B)</p> Signup and view all the answers

    What happens to the internal cohesion of liquid water when hydrogen bonds are disrupted?

    <p>It decreases significantly (B)</p> Signup and view all the answers

    Flashcards

    Water's abundance in living organisms

    Water makes up a significant portion (70% or more) of most living organisms.

    Role of water in early life

    Early life forms likely arose and evolved in an aqueous environment.

    Water's influence on cell function

    Cell structure and function are adapted to water's physical and chemical properties.

    Importance of weak water interactions

    Attractive forces and ionization tendencies in water significantly impact biomolecule structure and function.

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    Hydrogen bonds in water

    Hydrogen bonds create cohesive forces in water, making it a liquid at room temperature, and impacting its crystalline structure.

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    Solubility of biomolecules in water

    Polar biomolecules dissolve readily in water because they can replace water-water interactions with more favorable water-solute interactions.

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    Water's role in biomolecule recognition

    Water's ability to form hydrogen bonds with biomolecules significantly influences their recognition due to its solvent properties.

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    Water's importance for biological buffering

    Aqueous solutions of weak acids or bases and their salts act as buffers maintaining pH stability.

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    Nonpolar biomolecules

    Biomolecules that do not interact with water molecules and have low solubility in water.

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    Water solubility

    How easily a substance dissolves in water.

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    Hydrogen bond

    A weak attraction between a hydrogen atom in one molecule and an electronegative atom (like oxygen) in another.

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    Partial Charges

    Unequal sharing of electrons in a molecule creates a positive charge on one atom and a negative on another.

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    Electronegativity

    The tendency of an atom to attract electrons towards itself when bonded to another atom.

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    Water's high melting/boiling point

    Water has higher melting and boiling points than other similar solvents due to strong hydrogen bonding.

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    Heat of vaporization

    The energy needed to turn a liquid into a gas.

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    Cohesion

    Attraction between like molecules.

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    Sp3 bonding orbitals

    Type of bonding orbital associated with carbon and other atoms.

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    Study Notes

    Water's Abundance and Importance in Living Systems

    • Water constitutes 70% or more of most organisms' weight.
    • Early life arose in aqueous environments.
    • Evolution has been shaped by water's properties.
    • Cell structure and function are adapted to water's properties.

    Water's Physical and Chemical Properties

    • Water's attractive forces and ionization are vital to biomolecules.
    • Ionization is reviewed using equilibrium constants, pH, and titration curves.
    • Aqueous solutions of weak acids/bases and salts act as buffers against pH changes.
    • Water molecules and their ions (H⁺ and OH⁻) influence cellular components (proteins, nucleic acids, lipids).
    • Noncovalent interactions among biomolecules are significantly affected by water's solvent properties and hydrogen-bonding ability.

    Weak Interactions in Aqueous Systems

    • Hydrogen bonds between water molecules create cohesive forces, making water a liquid at room temperature.
    • Crystalline water (ice) has an especially ordered structure due to hydrogen bonds.
    • Polar biomolecules dissolve readily in water (replace water-water interactions with water-solute interactions).
    • Nonpolar biomolecules disrupt water-water interactions and are poorly soluble (tend to cluster together).
    • Hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals forces collectively affect biomolecule structures.

    Hydrogen Bonding in Water

    • Water's high melting point, boiling point, and high heat of vaporization are a result of strong intermolecular attractions.
    • Water's electron structure creates uneven electron sharing (oxygen is more electronegative).
    • This results in water molecules having two electric dipoles, with partial positive charges on hydrogen and a partial negative charge on oxygen.
    • Electrostatic attraction (hydrogen bond) forms between water molecules.
    • Hydrogen bonds are relatively weak (bond dissociation energy ~23 kJ/mol compared to 470 kJ/mol for covalent O-H bond).
    • Hydrogen bonds are represented with 3 parallel blue lines in the text
    • The shape of the water molecule is nearly tetrahedral with a bond angle of 104.5 degrees.

    Additional Information

    • Examples of solvents (melting point, boiling point, heat of vaporization) are given in a table.
    • Diagrams show the structure of the water molecule and hydrogen bonding.

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    Description

    Explore the critical role of water in living organisms and its unique properties that make it essential for life. This quiz covers the physical and chemical properties of water and its influence on biological structures and functions. Test your knowledge on how water impacts evolution and cellular interactions.

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