Unit 1 Molecules Test: Water, Water Potential, Nucleic Acids and DNA Replication
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Define metabolism.
Metabolism = the sum of all enzyme-catalyzed chemical reactions in an organism, including anabolism (building) and catabolism (breaking down). Keyword: enzyme-catalyzed reactions.
Why is water called the “medium for life”?
Water is the solvent of metabolism → dissolves polar/ionic molecules, allowing biochemical reactions to occur. It also provides transport of substances, temperature regulation, and a stable aquatic environment.
What is the evidence that life originated in water?
(1) Cells are ~70% water, (2) universal solvent for biomolecules, (3) deep-sea vent hypothesis suggests life began in aqueous, mineral-rich hydrothermal vents.
What is the molecular formula of water?
H₂O.
Draw and describe the atomic structure of water.
Oxygen atom covalently bonded to two hydrogens; bent structure (~104.5°).
Why is water polar?
Electrons pulled toward oxygen (higher electronegativity) → creates partial negative charge (δ–) on O and partial positive charges (δ+) on H.
Describe hydrogen bonds.
Weak intermolecular attractions between δ+ H of one molecule and δ– O of another.
Contrast covalent vs hydrogen bonds.
Covalent = intramolecular, strong, shared electrons; Hydrogen = intermolecular, weak, attraction between partial charges.
Define cohesion.
Attraction between water molecules due to hydrogen bonding.
Contrast adhesion and cohesion.
Cohesion = water to water; Adhesion = water to another polar/charged surface.
Example of cohesion beneficial to life?
Surface tension → allows small organisms (e.g. water striders) to walk on water.
Define adhesion
Attraction of water molecules to polar/charged surfaces
Define capillary action.
Movement of water against gravity in narrow tubes due to adhesion to walls + cohesion between molecules.
Example of adhesion beneficial to life?
Water climbing xylem walls → essential for plant water transport.
Effects of capillary action in soil?
Distributes water and dissolved minerals through soil pores → available for roots.
How does capillary action supply plants with nutrients?
Water adheres to xylem walls and carries dissolved minerals upward to leaves.
Why is water a good solvent?
Water’s polarity allows it to form hydration shells around ions and H-bond with polar molecules → prevents them from clustering.
Why are nonpolar molecules hydrophobic?
Cannot form favorable interactions; disrupt H-bonding network → excluded from water.
How are hydrophilic molecules transported in blood?
Dissolved in plasma (e.g. glucose, amino acids, Na⁺, Cl⁻).
Why are polar/ionic molecules hydrophilic?
They form favorable interactions (hydrogen bonds/ion-dipole) with water.
Classify these as hydrophilic or hydrophobic: amino acids, cholesterol, fats, oxygen.
Amino acids → hydrophilic; cholesterol/fats → hydrophobic; O₂ → hydrophobic.
Why must some molecules be hydrophobic?
Hydrophobic molecules (e.g. phospholipids) are insoluble, forming membranes and enabling barrier function.
Name three thermal properties of water useful for organisms.
(1) High specific heat → stable environment. (2) High latent heat of vaporization → cooling by sweating/evaporation. (3) High boiling point → remains liquid over wide temp range.
Two examples of adaptations to survive in water?
(1) Antifreeze proteins in fish prevent ice crystal growth. (2) Streamlined bodies reduce resistance in dense medium.