water

structure

  • (di)polar molecule → solvent (where reactions take place)

    • shared electrons pulled to O atom → slightly neg charge. H atom → slightly pos charge

    • both pos + neg poles → dipolar

water molecules can form H bonds

δ- O end and δ+ H end → water molecules interact w each other.

hydrogen bond: δ+ H end of one water molecule attracts towards δ+ H end of another molecule

roles of water

  1. solvent - lots substances dissolve in water

    • ionic compounds (made of pos+neg ions) split apart when added to water.

  2. buffer temp fluctuations - makes/maintains stable conditions (reactions). high SHC bc of H bond. more stable = less energy. bonded = less energy

  3. cooling mechanism/sweating - large latent heat, more H bonds needed to break

  4. habitat - organisms survive/reproduce in water

  5. metabolite in condensation + hydrolysis reactions

  6. transport - organisms use to move substances

water as solvent

many substances within cells are ionic compounds, means they consist of positive + negative ions (e.g. salt made up of Na+ + Cl- ions). When these ionic compounds are added to water, ions are split apart

water is polar so slightly neg oxygens attracted to pos ions whilst slightly pos hydrogens attracted to neg ions

each ion surrounded by water molecules + compound dissolves 

water known as universal solvent bc it dissolves more substances than any other liquid

useful for following reasons: 

  • most biological reactions take place in solution - ex in cytoplasm of eukaryotes/prokaryotes

  • dissolved substances can be transported around body - ex ions can be transported in blood plasma

water as temp buffer

  • has high specific heat capacity, requiring much energy to raise 1g of water by 1°C.

  • Hydrogen bonds absorb energy, making them hard to break + heat water.

  • High SHC makes water resist rapid temp changes.

  • Organisms made of water maintain stable body temp

    • SHC can be defined per 1g or 1kg, depending on units used in calculations

water as cooling mechanism

  • Hydrogen bonding requires much energy to evaporate 1g of water.

  • has high latent heat of vaporization, needing signif energy to turn from liquid → gas.

  • Organisms use water evaporation for cooling w out losing much water.

  • evaporation from skin takes heat energy away, cooling organism

water as habitat

  • high SHC and LHV create stable environment.

  • water freezes → less dense ice, floats.

    • floating ice insulates ponds + lakes

    • water below ice stays unfrozen, allowing organisms to survive

water as metabolite

  • involved in many chemical reactions in organisms:

    • Hydrolysis: uses water to break down molecules

    • Condensation: releases water to join molecules

    • Photosynthesis: uses water as raw material

water as transport medium

  • Cohesion: Water molecules stick together via hydrogen bonds.

  • Adhesion: Water sticks to other materials.

  • Cohesion and adhesion help water flow through organisms, transporting substances.

  • In plants, cohesion and adhesion allow water to move through the xylem.

  • Water's high surface tension creates skin-like surface that supports small organisms like pond-skaters.