water

Question 1

why is water a polar molecule

Answer 1

dipolar - no overall charge, however, O is slightly negative, H is slightly positive - molecule has slightly positive and negative poles

Question 2

why is water significant for living organisms

Answer 2

solvent for polar molecules during metabolic reactions
enables organisms to avoid fluctuations in core temperature (high shc)
cohesion-tension of water molecules in the transpiration stream

Question 3

what are inorganic ions and where are they found

Answer 3

ions that do not contain C atoms, found in cytoplasm and extracellular matrix fluid, may be very high or low in concentration

Question 4

explain the role of H atoms in the body

Answer 4

high conc of H+ ions - low pH (acidic)
H+ ions interact with H bonds and ionic bonds in the tertiary structure of proteins which can cause them to denature

Question 5

explain the role of Fe ions in the body

Answer 5

Fe2+ bonds to porphyrin ring to form haem group in haemoglobin (quaternary structure)
haem group has binding site to hold on O2 molecule around the body through the bloodstream
4 haem groups per haemoglobin molecule

Question 6

explain the role of Na ions in the body

Answer 6

involved in co-transport for absorption of glucose and amino acids in the lumen of the gut
involved in propagation of action potentials in neurons

Question 7

explain the role of phosphate ions in the body

Answer 7

component of DNA, ATP, NADP, cADP

Question 8

describe the specific heat capacity of water

Answer 8

water molecules stick together, req more energy (heat) to separate them. takes much energy to heat a given mass of water. acts as a buffer against sudden temp changes. makes aquatic environment temp-stable. organisms are mostly water, can retain heat and are protected form sudden temp changes esp in terrestrial environments

Question 9

describe the latent heat of water

Answer 9

H bonds between water molecules means requires much energy to evaporate 1g of water (high latent heat of vaporisation) evaporation of water such as sweat is an effective means of cooling the body, req a lot of body heat to evaporate the water

Question 10

describe cohesion and surface tension of water

Answer 10

H bonding gives water large cohesive forces. this allows it to be pulled up through a tube eg xylem vessels in plants. where water meets air, they tend to be pulled back into the body of water rather than escaping from it. surface tension acts like a skin and is strong enough to support small organisms such as pond skaters

Question 11

describe the importance of water in metabolism

Answer 11

water is used in hydrolysis
chemical reactions take place in aqueous mediums
water is a major raw material in photosynthesis

Question 12

describe how water is used as a solvent

Answer 12

readily dissolves substances such as
gases - CO2 and O2
wastes - ammonia and urea
inorganic ions and small hydrophilic ions - amino acids, monosaccharides and ATP
enzymes, whose reactions take place in solution

Question 13

why is the evaporation of water useful to organisms

Answer 13

it requires body heat to evaporate as sweat, therefore cooling organisms, allows them to control their temperature

Question 14

how does water provide support

Answer 14

it is not easily compressed and therefore provides support eg turgor pressure in herbaceous plants

Question 15

how is water’s transparency useful

Answer 15

aquatic plants can photosynthesise and light rays can pass through the fluid that fills the eye and so reach the retina