-1B: water

Question 1

outline useful properties of water

Answer 1

-metabolite, includes condensation + hydrolysis reactions
-good solvent, some substances can dissolve in it, most metabolic reactions are in solutions -> essential
-helps in temperature control, due to high latent heat of vaporisation + specific heat capacity
-water molecules are cohesive (stick together) helps in transportation in plants + other organisms

Question 2

outline structure of a water molecule

Answer 2

-molecular formula: H2O
-one molecule of oxygen bonded to 2 molecules of hydrogen
-shared pair of negative electrons in hydrogen attracted to oxygen, leaving other side of hydrogen atom with slightly positive charge (delta positive)
-2 lone pairs on oxygen mean it has a slight negative charge (delta negative)

Question 3

how does hydrogen bonding happen in water molecules?

Answer 3

-negative oxygen attracts positive charged hydrogens on neighbouring water molecules + vice versa
-polarity + hydrogen bonding means it has a number of useful properties

Question 4

name the useful properties of water

Answer 4

-metabolite
-high latent heat of vaporisation
-buffer changes in temperature
-good solvent
-strong cohesion between molecules

Question 5

metabolite?

Answer 5

-many metabolic reactions involve hydrolysis + condensation reactions
-condensation: formation of a new chemical bond between 2 monosaccharides + release a molecule of water
-hydrolysis: breaking of a chemical bond through addition of water molecule
-eg amino acids -> polypeptide, ATP -> ADP + Pi

Question 6

high latent heat of vaporisation?

Answer 6

-large amount of heat energy required to break hydrogen bonds between water molecules
-high latent heat of vaporisation -> large amount of energy used up when water evaporates
-useful in organisms as they can cool down through water loss in evaporation without losing a large amount of water (eg sweating)

Question 7

buffer changes in temperature?

Answer 7

-hydrogen bonds absorb large amounts of energy
-high specific heat capacity -> large amount of energy needed to raise temperature of 1g of water by 1C
-useful in organisms as water doesnt undergo rapid temperature changes -> good habitat, especially underwater as stable temperatures
-water inside organisms remains at fairly stable temperature -> maintains constant internal body temperature

Question 8

good solvent?

Answer 8

-most important substances in metabolic reactions = ionic (one positively charged ion + one negatively charged ion)
-negatively charged ion attracts delta positive (H) ends of water, positively charged ion attracts delta negative (O) end of water -> surrounds ions by water molecules -> dissolves
-waters polarity makes it a useful solvent

Question 9

strong cohesion?

Answer 9

-cohesion: strong attraction between two molecules of the same type
-water = strong cohesion due to polarity
-strong cohesion helps water flow -> useful for transporting substances eg travelling up xylem columns
-strong cohesion -> high surface tension when comes into contact with air, reason why sweat forms droplets which evaporate from skin to cool an organism down