3.1.7 water

Question 1

water as a metabolite

Answer 1

-water is a metabolite in many metabolic reactions e.g. condensation/hydrolysis reactions

Question 2

water as a solvent

Answer 2

water is a solvent, most metabolic reactions take place in a solution e.g. in the cytoplasm of eukaryotic/prokaryotic cells

Question 3

water and temperature control

Answer 3

water helps with temperature control due to its high latent heat of vaporisation/high specific heat capacity

Question 4

water molecules and cohesion

Answer 4

water molecules are very cohesive = helps water transport in plants and transport in other organismn

Question 5

structure of water molecule

Answer 5

1 atom of oxygen joined to 2 atoms of hydrogen by shared electrons

Question 6

in a water molecule what charge does the other side of each H atom have and why?

Answer 6

as the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight + charge (delta +)

Question 7

what charge does the oxygen atom in a water molecule have and why?

Answer 7

the unshared negative electrons on the oxygen atom give it a slight - charge (delta -)

Question 8

are water molecules non-polar or polar?

Answer 8

polar

Question 9

why are water molecules polar?

Answer 9

it has a partial - charge on one side and a partial + charge on the other

Question 10

what are hydrogen bonds?

Answer 10

weak bonds between a slightly + charged H atom in 1 molecule and a slight - charged atom in another molecule

Question 11

why do hydrogen bonds form between water molecules?

Answer 11

slightly - charged oxygen atoms of water attract the slightly + charged hydrogen atoms

Question 12

what do many metabolic reactions involve?
(water as an important metabolite)

Answer 12

a condensation or hydrolysis reaction

Question 13

how does a condensation reaction involve a water molecule?
(water as an important metabolite)

Answer 13

condensation reaction releases a water molecule as a new bond is formed

Question 14

how does a hydrolysis reaction involve a water molecule?
(water as an important metabolite)

Answer 14

hydrolysis reaction requires a molecule of water to break a bond

Question 15

why is water a good solvent (ions)?
(water as a good solvent)

Answer 15

as water’s polar, the slight + charged end of a water molecule is attracted to the negative ion and the slightly - end of a water molecule is attracted to the + ion

Question 16

why is it helpful for water to be a good solvent?

Answer 16

living organisms can take up useful substances e.g. mineral ions dissolved in water and these dissolved substances can be transported around the body

Question 17

why does water have a high latent heat of vaporisation?

Answer 17

takes a lot of energy to break the hydrogen bonds between water molecules, so a lot of energy is used up when water evaporates

Question 18

why is it useful for water to have a high latent heat of vaporisation?

Answer 18

means living organisms can use water loss through evaporation to cool down without loosing too much water

Question 19

why does water have a high specific heat capacity?

Answer 19

when water is heated, lots of the heat energy is used to break the hydrogen bonds between the water molecules so there is less heat energy available to increase the water’s temperature

Question 20

why is it useful for living organisms that water has a high specific heat capacity?

Answer 20

means water doesn’t experience rapid temperature changes

Question 21

what are the positives of water not experiencing rapid temperature changes?

Answer 21

makes water a good habitat as the temperature under water is more likely to be stable than on land. water inside organisms also remains at a fairly stable temperature - helps maintain constant internal body temp

Question 22

what is cohesion?

Answer 22

attraction between molecules of the same type

Question 23

why are water molecules very cohesive?

Answer 23

as they are polar

Question 24

why is water’s strong cohesion useful?

Answer 24

-helps water to flow so it is good for transporting substances
-water has a high surface tension when it comes into contact with air e.g. the reasons sweat droplets form which help to cool down