A1.1 Water Flashcards
Water as the medium for life
Life on earth began in the ocean (+ vesicles)
Substances dissolved in water -> chem. reactions between solutes.
Molecules bent rather than linear -> Hydrogen on the same side and form one pole. H2O is dipolar.
Electronegativity
A chemical property that describes the tendency of an atom to attract electrons toward itself.
Electronegativity of H2O
O pulls H electrons towards it. O = δ- (partial neg.) and H = δ+
Hydrogen bonding
Electrostatic attraction between H atom in a polar molecule and a small electroneg. atom (O, N, or F) in another.
Cohesion
Alike molecules sticking togehter due to intermolecular forces of attraction (e.g. hydrogen bonds).
Conduction of water in the xylem
Cohesion allows transport of water w/ help of tension.
Roots = soil particles + water attract
Leaves = water evap. atm. and attraction water molecules + cell wall of leaf cells.
Why does water move upwards in the xylem?
Pulling forces in the leaves > forces in the roots.
Surface tension (water)
An elastic-like membrane that forms because water molecules are more attracted to each other in hydrogen bonding than to air particles.
Why does surface tension make it possible for objects to float?
Cohesion between water molecules > attraction between water and floating object. (some animals use this to inhabit water surfaces)
Object break through -> many hydrogen bonds must be broken simultaneously.
Adhesion
When hydrogen bonds form between water and the surface of a solid composed of polar molecules. -> Water sticks to the surface.
Capillary action
When liquid flows through narrow spaces without external forces, rather, the liquid’s movement is aided by intermolecular forces between the liquid and solid surface(s).
Occurs: adhesion to the walls > cohesive forces liquid molecules.
Capillary action glass tube
As air is replaced by water, many H bonds form between glass and water, releasing energy.
Why can porous solides such as paper exert strong suction forces through adhesion?
They have a large amount of surface area to attract water.
How water can rise up from an underground source, even though gravity tends to pull it down?
Water is attracted to many chemical substances in soil. If soil is porous, water is drawn by capillary action through dry soil, wetting it.
Capillary action usefulness in leaves
Water evaporates from cell walls -> lost to atm. -> adhesive forces draw water out nearest xylem vessel.
This keeps the walls moist -> can absorb CO2 needed for photosynthesis. Also generates low pressures that draw water up xylem vessels.
Capillary action usefulness refill xylem
Xylem vessel becomes air-filled -> adhesion between water + wall of vessel helps vessel to refill with water.
Solvent
Substance capable of dissolving other substances.
Solute
A dissolved substance (present in a smaller amount than the solvent in a solution).
Solution
A mixture of one or more solutes dissolved in a solvent.
Water important solvent properties
H2O polar -> forms shells around charged + polar molecules. Prevents clumping so they remain in solution.
Partial neg. attracted to cations + partial pos. attracted to anions -> both dissolve.
H2O forms H-bonds w/ polar molecules.
Hydrophilic
Substances chemically attracted to water. All dissolve in water (polar or charged).
Substances that water adheres to but does not dissolve (e.g. cellulose) also hydrophilic.
Hydrophobic
Not repelled by water but not attracted -> more attracted to other hydrophobic subst.
Non-polar + not charged. -> Insoluble in water but may dissolve in other solvents.
All lipids are hydrophobic.
Water as a medium for metabolism
Cytoplasm = is an aqueous solution and solvent is water. Solutes move around + interact.
Metabolism in the cytoplasm
Diff. chem. reactions catalysed in cytoplasm collectively known as metabolism.
Without water, the components of reactions can’t come together on enzymes active sites.
Transport in plants
Substances transported as an aqueous solution.
Minerals ions transported in xylem sap. Sucrose + products of photosyn. in phloem sap.
Transport in blood - ions
NaCl = soluble -> dissolved to Na+ and Cl-
Transport in blood - amino acids
Soluble: have neg. + pos. charges -> solubility varies depending on variable molecule part, phillic or phobic.
Transport in blood - glucose
Polar molecule -> soluble.
Transport in blood - oxygen
Non-polar (dioxygen) -> small size = dissolve water sparingly -> saturates H2O at low conc.
Temp. rises -> solubility decreases.
Haemoglobin binding sites for O increases capacity of O transport around body for aerobic cell resp.
Transport in blood - fat molecules
Non-polar -> insoluble -> coalesce = form large droplets in blood.
Small drops coated single layer phospholip. -> prevent water contact -> small drops suspended while transported.
Buoyancy
Object immersed in fluid -> fluid exerts upward force on object (= weight fluid displaced).
Object density < fluid density THEN force acting on object > force due to gravity. So the object floats.
How does buoyancy make water habitable?
Living organisms have overall denisty close to water -> easier to use as habitat than air as not much energy needed to float and more needed energy to stay airborne.
Viscosity
A fluids resistance to flow due to its internal friction (H-bonds) when one part of fluid moves relative to another.
Viscosity complications habitat
Solutes increase viscosity -> seawater higher viscosity due to dissolved salts -> more resistance is met for an animal trying to move through water.
Thermal conductivity
Rate at which heat passes through a material.
Water has relatively high TC -> useful when there is a need to absorb and transfer heat.
Specific heat capacity
The heat required to raise the temperature of 1g of a material by 1°C.
Water relatively high HC -> a lot of energy needed to break H-bonds -> stable temps.
Extraplanetary origin of water on
Earth
Likely asteroids that collided w/ Earth early in its history contained more water.
Water was retained on Earth after its delivery by asteroids, two factors are significant:
Distance to Sun = sunlight never raises temps for boil. Liquid water retained easier than vapour bc cohesion from H-bonding.
Earth size = relatively strong gravity -> holds oceans tightly to surface + gases in the atm.
Goldilocks zone
Habitable zone around a star.
Planet is too close = water vaporize.
Too far = water freezes.
Depends: star size + amount energy emits. Planet size determine gravity strength + atm pressure.
