M2.2 - WATER: Reaction Medium of the Cell

• bent/ Vshaped

• molecular geometry: ____________

• has four electron groups around oxygen which are nearly tetrahedral in arrangement

• electronegative O and 2 H atoms forms a dipole

  • water is a polar molecule

• hydrogen

• bent structure of water is important in _____________ bonding

• water can serve both as a H-donor and acceptor

• potential to form 4 H bonds per water molecule

• high

• high

• high

• high

• high

• liquid

• solvent

Unique Properties of Water allows water to sustain life on Earth

• __________ cohesion

• __________ adhesion

• __________ surface tension

• __________ specific heat

• __________ heat of vaporization

• __________ at room temperature

• excellent __________

• hydrophobic exclusion

• cohesion

• adhesion

High Cohesion and Adhesion of Water

• ___________ – “act of sticking together”

• ___________– “act of sticking to something”

  • due to the ability of water molecules to form H-bonds

Cohesion; Adhesion

High ___________ and ___________ of Water

• important for the transport of water from roots to other parts of a plant

  • direction is against the pull of gravity

  • major component of plant cell walls is cellulose which can form H-bonds with water molecule

surface tension

_______________ – a measure of the resistance of a substance to increase its surface area

• due to high cohesion of water molecules

Surface Tension

High ______________ of Water

• importance

  • cause things/animals denser than water to float

  • allows formation of water droplets

• specific heat

Moderation of Temperature by Water

• by absorbing heat from warmer air and releasing that heat to cooler air

  • due to high ______________ of water

    • – amount of heat per unit mass required to raise the temperature by 1 °C

    • for water: 1 cal/ g-°C

• faster

  • breakin; absorbs

• slower

  • formation; releases

Moderation of Temperature by Water

• for water to have an increase in T, its molecules should move __________ (due to increase in KE)

  • causes __________ of H-bonds which ___________ heat

• for water to have a decrease in T, its molecules should move __________(due to decrease in KE)

  • causes __________ of H-bonds which ____________heat

• gradual

• internal body

Moderation of Temperature by Water

importance:

• regulate the rate of change in air’s temperature especially near oceans

  • __________ instead of sudden

• regulation of organism’s ______________ temperature

Evaporative Cooling

• heat of vaporization

__________________

• process at which as liquid evaporates, the liquid surface that remains behind cools down

  • due to high __________________ of water

    • – amount of heat needed to turn 1 g of liquid into a vapor without a rise in temperature of the liquid

    • for water: 540 cal/g at 25 °C

Evaporative Cooling

_____________________ of Water

• due to the presence of a hydrogen bonding network between water molecules, a high input of energy is required to transform 1 gram of liquid water to water vapor

Evaporative Cooling

_____________________ of Water

• importance

  • sweating

  • evaporation of water at the surface of leaves

• four

• 3.4

Floating of Ice on Liquid Water

• in ice, water molecules form a maximum of _______ H-bonds, creating a regular crystal lattice

• in liquid water, water molecules form an average of _______ H-bonds with each other

• fewer

• less

• insulation

Floating of Ice on Liquid Water

• ice crystal is spacious as it has __________ molecules than in equal volume of liquid water

• ice is _________ dense than water

• importance:

  • floating ice forms a layer of _____________ on tops of lakes and seas

  • helps life to survive on Earth (example: marine organisms)

• dielectric constant

Excellent Solvent

• as polar solvent, water readily dissolves other polar compounds and salts via

  • due to high __________________ of water

    • – measure of the ability of a solvent to keep opposite charges apart

• oppositely; dipoles

• hydration

Excellent Solvent

• ions attracts the ___________ charged ends of the resulting water _________

  • ions are surrounded by water molecules (__________)

    • attenuates coulombic forces between ions

• amphiphiles

Hydrophobic Effect

• for ___________, water tends to hydrate its hydrophilic portion and to exclude its hydrophobic portion

Hydrophobic Effect • 1. presence of amphiphiles disrupt H-bonding between water molecules • water molecules surround each amphiphile molecule • not favored because of the resulting highly-ordered structure (decrease in entropy of the system)