A1.1 - water

Question 1

hydrophobic

Answer 1

not attracted to water

Question 2

hydrophilic

Answer 2

attracted to water

Question 3

organelle

Answer 3

sub-cellular structures such as mitochondrion

Question 4

how did the first cells originate in water?

Answer 4

• oceans provided the solvent for biochemical reactions
• membranes evolved to separate the water in the cytoplasm from “ocean water”

Question 5

what processes does water remains the medium in which they occur?

Answer 5

• making up cytoplasm in cells
• making up fluids inside organelles
• making up tissue fluid or fluids between cells
• transporting molecules around organisms and inside or outside of cells
• range of habitats

Question 6

what is the bonding of water?

Answer 6

hydrogen bonding between water molecules due to partial positive charge of hydrogen and partial negative charge of oxygen

Question 7

why is water a polar substance?

Answer 7

unequal sharing of electrons within the water molecule (unsymmetrical)

Question 8

cohesion

Answer 8

attraction of water to other water molecules

Question 9

why does cohesion occur?

Answer 9

occurs due to hydrogen bonding as it allows water molecules to influence each other, causing continuous motion of water molecules through the short-lived bonds

Question 10

what are the applications of cohesion?

Answer 10

• transport of water under tension in the xylem against gravity as a column of water molecules
• water surfaces as habitats due to surface tension effect

Question 11

adhesion

Answer 11

water’s attraction to other molecules due to hydrogen bonding
- can be polar or charged materials

Question 12

what are the consequences of adhesion?

Answer 12

capillary action
- in the soil, water moves through microscopic channels
- in plant cells, adhesion to cellulose generates tension and aids the upwards movement of water and stopping it from dropping in the xylem

Question 13

what type of substances dissolve in water?

Answer 13

polar molecules - such as glucose where the partially negative charges on the solute are attracted to the partially positive charges on the water molecules
ionic substances - partially positive hydrogen is attracted to negative ion and partially negative oxygen is attracted to the positive ion

Question 14

how is water used by enzymes?

Answer 14

enzymes catalyse reactions in aqueous solutions as they are proteins which dissolve in the water of cytoplasm and allow reactions to occur at a fast rate to support life functions

Question 15

what state is water at room temperature?

Answer 15

liquid meaning that dissolved molecules can flow such as water transported in xylem contains dissolved minerals such as potassium

Question 16

what are hydrophobic molecules?

Answer 16

insoluble in water but can pass through cell membranes - steroid hormones can pass through plasma and nuclear membrane to influence gene expression

Question 17

what are membrane-bound proteins?

Answer 17

proteins that have hydrophobic regions (cell membrane) and hydrophilic regions (cytoplasm)
- hydrophobic regions keeps the protein attached to the membrane

Question 18

what are epidermal cells?

Answer 18

cells in leaves that secrete a hydrophobic wax that forms a cuticle and acts as a barrier to reduce water loss through evaporation

Question 19

buoyancy

Answer 19

upward force exerted on an object, equal to weight of the displaced medium

Question 20

viscosity

Answer 20

resistance to an object moving through a medium

Question 21

thermal conductivity

Answer 21

ability of a substance to transfer heat

Question 22

specific heat capacity

Answer 22

energy required to raise 1kg of a substance by 1C

Question 23

what is buoyancy like in water and air?

Answer 23

water - big upward force due to increased pressure from water below than air above (allowing organisms to float)
air - small upward force as weight of air displaced is less than the same volume of water

Question 24

what is viscosity like in water and air?

Answer 24

water - more dense so has a higher viscosity
air - less dense so has a lower viscosity

Question 25

what is thermal conductivity like in water and air?

Answer 25

water - high thermal conductivity
air - low thermal conductivity

Question 26

what is specific heat capacity like in water and air?

Answer 26

water - high specific heat capacity as a lot of energy is needed to break the hydrogen bonds
air - low specific heat capacity as less energy is needed to change the temperature of the gas

Question 27

what are characteristics of the black throated loon in response to water’s physical properties?

Answer 27

Black-throated loon - bird that lives in cold regions of the Northern Hemisphere
- high buoyancy of water allows the bird to stay in water for long period of times
- webbed feet and streamlined body helps overcome high viscosity so less energy is needed
- glands produce oil to waterproof the feathers
- high thermal conductivity means that birds lose more body heat on water
- water is warmer in cold weather due to high specific heat capacity

Question 28

what are characteristics of the ringed seal in response to water’s physical properties?

Answer 28

Ringed seal - found in cold regions of the Northern Hemisphere
- high buoyancy of water allows the ringed seal to keep snout above water to access air
- padded feet and streamlined body helps overcome high viscosity so less energy is needed
- thick blubber minimises heat loss and provides insulation and protection to internal organs
- water is warmer in cold weather due to high specific heat capacity