water

Question 1

describe the structure of water

Answer 1

-non linear (v shaped)
-dipolar (oxygen atom is slightly negative, hydrogen atom slightly positive)

Question 2

where do hydrogen bonds form between water molecules?

Answer 2

between an oxygen molecule (slightly negative) in one and a hydrogen molecule (slightly positive) in another

Question 3

what is the name for when water hydrogen bonds to other water molecules?

Answer 3

cohesion

Question 4

what is the name for when water hydrogen bonds to something else e.g xylem walls?

Answer 4

adhesion

Question 5

why is water a polar solvent?

Answer 5

it has a dipole

Question 6

why is ice less dense than water?

Answer 6

hydrogen bonds in ice hold the molecules further apart in a fixed lattice, whereas in water the molecules are closer together and so it is denser.

Question 7

explain what it means when water is described as having a high specific heat capacity

Answer 7

liquid water molecules can absorb a lot of heat energy without a large increased in temperature (temperature remains relatively constant)

Question 8

explain what it means when water is described as having a high specific latent heat of vaporisation

Answer 8

liquid water can absorb a lot of heat energy before changing state from a liquid to a gas

Question 9

what is the biological significance of ice being less dense than water?

Answer 9

ice floats on top of water and so provides a layer of insulation to aquatic habitats whilst still allowing organisms to move underneath it

Question 10

what is the biological significance of water having a high specific heat capacity?

Answer 10

minimises temperature fluctuation in aquatic habitats

Question 11

what is the biological significance of water having a high specific latent heat of vaporisation?

Answer 11

has a role in cooling the body through sweating

Question 12

what is the biological significance of water being a polar solvent?

Answer 12

allows reactions to occur

Question 13

what is the biological significance of water having a high surface tension?

Answer 13

-allows insects to walk on the water’s surface by adhesion
-allows water to be pulled through plants (transpiration)

Question 14

what is the biological significance of water being a liquid at most temperatures on earth?

Answer 14

-used as a medium for chemical reactions
-helps to transport chemicals

Question 15

what is the biological significance of water being transparent?

Answer 15

light can pass through to aquatic plants for photosynthesis

Question 16

define osmosis

Answer 16

passive movement of water down the water potential gradient across a partially permeable membrane

Question 17

define water potential

Answer 17

a measure of how freely water molecules can move

Question 18

describe some features of water potential

Answer 18

-maximum value of 0 (pure water) -> never positive
-measured in kPa

Question 19

why does salty water have a lower water potential than pure water?

Answer 19

the ions ‘stick’ water molecules to them which prevents them from moving as freely

Question 20

define hypotonic in terms of solute concentration

Answer 20

low solute concentration (so high water concentration)

Question 21

define hypertonic in terms of solute concentration

Answer 21

high solute concentration (so low water concentration)

Question 22

what happens to an animal cell when it is placed in a hypotonic solution?

Answer 22

higher water potential outside cell, so net movement of water into cell by osmosis. this causes the cell to burst (lysis)

Question 23

what is the name for when a blood cell undergoes lysis?

Answer 23

haemolysis

Question 24

what happens to an animal cell in a hypertonic solution?

Answer 24

higher water potential inside cell, so net movement of water out of cell by osmosis. this causes the cell to shrivel (crenate)

Question 25

what happens to an animal cell in an isotonic solution?

Answer 25

same water potential inside and outside cell so no net movement of H2O

Question 26

what happens to a plant cell in a hypotonic solution?

Answer 26

net movement of water into the cell cytoplasm and vacuole. this causes it to become turgid

Question 27

what happens when a plant cell becomes turgid?

Answer 27

the cytoplasm pushes against the cell wall. the cell wall resists as it is inelastic and exerts the same pressure back on the cytoplasm, which prevents more water from entering

Question 28

what happens to a plant cell in an isotonic solution?

Answer 28

50% of cells are plasmolysed and 50% are not as each cell has a slightly different water potential

Question 29

what happens to a plant cell in a hypertonic solution?

Answer 29

net movement of water out of cell cytoplasm and vacuole, causing the cell membrane to pull away from the cell wall. the cell has been plasmolysed.

Question 30

how is water pulled through a xylem?

Answer 30

cohesion between water molecules moves them upwards, adhesion between water and xylem walls prevents the water from falling