MEMBRANES + FUNCTIONS

Question 1

why is water considered the medium of life?

Answer 1

the first cells originated in water and water remains the medium in which most life processes occur

Question 2

formation of hydrogen bonds

Answer 2

• 1 oxygen atom binds to 2 hydrogen atoms by sharing a pair of electrons (covalent bonds).
• The oxygen nucleus draws electrons away from the hydrogen nucleus
• The water molecule carries an unequal distribution of electrical charge. It is polar.
• The electrostatic attraction between the oppositely charged regions of 2 neighbouring molecules, gives rise to weak intermolecular forces called hydrogen bonds.

hydrogen bonds occur between water molecules, not within

Question 3

Draw two water molecules and the hydrogen bond between them.

Question 4

hydrogen bonds

Answer 4

a weak intermolecular force that exists when electronegativity creates a polar covalent bond (in water molecules)

Question 5

electronegativity

Answer 5

measures how strongly the nucleus of an atom attracts the electrons it shares with another

Question 6

factors affecting electronegativity

Answer 6

• no. of protons
• no. of orbital levels in the atom - more orbitals -> decreases the pull on shared electrons <- are further away from the nucleus + more shielding

Question 7

polar molecule

Answer 7

has an unequal distribution of electrical charge

Question 8

cohesion

Answer 8

attraction between 2 of the same substances

Question 9

adhesion

Answer 9

attraction between molecules of 2 different substances

Question 10

example of cohesion in trees

Answer 10

during transpiration, water is drawn up a tree trunk through xylem vessels: cohesive forces stop the water column from breaking and help draw water up the tree

Question 11

strength of hydrogen bonds

Answer 11

• not strong
• are weak intermolecular interactions
  (large cohesive forces in water arise from the fact there are many of them)

Question 12

what causes surface tension

Answer 12

when the molecules on the surface of the water have no other water molecules above them and so establish stronger attractive forces upon their immediate neighbouring molecules. (this results in the formation of spherical droplets)

Question 13

how do animals use surface tension to create a habitat

give an example

Answer 13

pond skaters - their waxy cuticle keeps them waterproof and their mass is not large enough to break the surface tension

Question 14

an example of adhesion

capillary action

Answer 14

the process by which water molecules are drawn up capillaries without suction. this is the result of water molecules adhering to the walls of those thin walls.

Question 15

when does capillary action occur

Answer 15

when adhesion is greater than cohesion

Question 16

how is capillary action used in plants

Answer 16

to move water from the soil into root hair cells. because plant root hair cells are made of porous cellulose that can act as a wick, water can be drawn in by capillary action. When water evaporates from the cell walls of the mesophyll and then leaves the plant through the stomata water is transported up the plant through adhesion & cohesion.

Question 17

solvent properties of water

Answer 17

• polar substances (e.g. Na+, Cl-) are very soluble in water -> the anions and cations become surrounded by a layer of water molecules
• non-polar substances (O2, N) are not very soluble -> do not form hydrogen bonds with water

Question 18

when are enzymes able to catalyse reactions

Answer 18

in aqueous solution

Question 19

state the physical properties of water

Answer 19

• buoyancy
• viscosity
• thermal conductivity
• specific heat capacity

Question 20

buoyancy

Answer 20

the ability of a fluid to exert an upward force on an object

Question 21

viscosity

Answer 21

a fluid’s resistance to objects passing through it

Question 22

thermal conductivity

Answer 22

a material’s ability to conduct heat

Question 23

specific heat capacity

Answer 23

the energy needed to raise one kilogram of a material by 1degree C

Question 24

state the adaptations of the ringed seal

Answer 24

• have low-density blubber to increase their buoyancy
• have a stream-lined shape to reduce drag against viscosity
• have insulating blubber with low thermal condictivity to reduce heat loss
• pups survive in lairs insulated by trapped air

Question 25

state the adaptations of the black-throated loon

Answer 25

• have large wings to generate lift in less buoyant air
• are hydrodynamic to reduce drag against viscosity
• are aerodynamic to reduce drag when flying
• have oiled exterior feathers to exclude water
• are insulated by trapped air in wings

Question 26

Goldilocks zone

Answer 26

refers to orbital distance from a star that will result in liquid water

Question 27

origin of water

Answer 27

from asteroids and meteorites containing liquid water

Question 28

properties of water as an aquatic habitat

Answer 28

• provides buoyancy
• has a high thermal conductivity
• has a higher viscosity than air
• has a high specific heat capacity
• is cohesive and adhesive
• an excellent solvent

Question 29

function of membranes

Answer 29

act as barriers and control the exchange of materials between the inside and outside of the crll

Question 30

where are membranes found?

Answer 30

surrounding cells and organelles in eukaryotes

Question 31

what are membranes made of

Answer 31

• lipids - phospholipids, glycolipids and cholesterol
• proteins
• small quantities of carbohydrates - glycolipids and glycoproteins

Question 32

hydrophobic

Answer 32

molecules which move away/are repelled by water

Question 33

hydrophilic

Answer 33

molecules which move towards/are attracted to water

Question 34

ampiphatic

Answer 34

have both hydrophilic and hydrophobic properties

e.g. phospholipid molecules

Question 35

how do phospolipids behave in water?

Answer 35

• in contact with water forming a monolayer - heads dissolved in water and tails sticking outwards
• mixing with water to form a bilayer - hydrophobic tails are attracted to each other