transporting across membranes

Question 1

what attracts other polar molecules

Answer 1

polar phosphate head

Question 2

how does a bilayer form

Answer 2

-hydrophobic fatty acid tails are oriented inwards towards the middle and point away from water and the
- hydrophobic heads are oriented towards the outside and point towards the water
- the hydrophilic heads make contact with watery cytoplasm and extracellular fluid

Question 3

what is the word to describe the cell surface membrane

Answer 3

selectively permeable

Question 4

what does the cell membrane consist of

Answer 4

proteins (channel / carrier / receptor )
glycoproteins
phospholipids
cholesterol
carbohydrates

Question 5

why is the cell membrane called the fluid - mosaic model

Answer 5

because phospholipids form a bilayer that are constantly moving around relative to one another giving the membrane a FLUID structure

different protein molecules are unevenly distributed throughout the membrane forming a MOSAIC

Question 6

what is the selective permeability of the cell membrane related to

Answer 6

type and distribution of specific proteins and phospholipid molecules present in the membrane

Question 7

what is the function of phospholipids in the cell membrane

Answer 7

form a bilayer (hydrophilic heads outwards in watery extracellular fluid or cytoplasm, hydrophobic tails inwards attracted to each other)

most abundant molecule in cell membrane

allows lipid-soluble (non polar) molecules ONLY to pass through simple diffusion

Question 8

what is the function of cholesterol in the cell membrane

Answer 8

decreases permeability and increases the stability of membrane

more cholesterol = less fluidity of membrane

different types of cells have different proportions of cholesterol

Question 9

what is the function of channel proteins

Answer 9

• are like pores that only allow specific charges ions or small molecules to pass through facilitated diffusion, they can be opened or closed and let ions pass right through
• proteins have a specific tertiary structure so they are specific and can only transport molecules that are complementary to the shape of channel protein

Question 10

how do Na+ ions pass through membrane

Answer 10

ONLY through sodium ion channel proteins

Question 11

what is the function of carrier proteins in the cell membrane

Answer 11

• aid the transport of ions / polar molecules and large molecules by facilitated diffusion and active transport

Question 12

what is the function of receptor proteins in the cell membrane

Answer 12

• act as specific receptors for complimentary molecules
• only specific molecules can bind to specific receptor proteins

Question 13

what is the function of glycoproteins in the cell membrane

Answer 13

• composed of carbohydrates and proteins and are important for cell to cell recognition (often acting as antigens)
• glycoproteins are produced in the golgi body

Question 14

what are aquaporins

Answer 14

special type of channel proteins specific to water ,cell that has lots of aquaporins is very permeable to water and carries osmosis easily

Question 15

what is simple diffusion

Answer 15

net movement of molecules from an area of higher concentration to lower concentration across a partially permeable membrane

Question 16

when does NET diffusion stop

Answer 16

when the molecules have reached equilibrium

Question 17

what molecules are transported using simple diffusion

Answer 17

non -polar , small , lipid-soluble molecules

Question 18

what is ficks law

Answer 18

rate of diffusion is proportional to = (surface area * conc gradient ) / diffusion distance

Question 19

what factors affect rate of diffusion

Answer 19

temperature- increased KE so faster rate of diffusion

surface area - larger SA more space for molecules to pass through

concentration gradient- as concentration difference increases, rate of diffusion increases

• diffusion distance

Question 20

what is facilitated diffusion

Answer 20

when specific proteins (carrier or channel) help specific molecules to pass through the phospholipid bilayer

Question 21

why can hydrophilic ( water soluble, charged or large ) substances not pass between hydrophobic tails

Answer 21

because the fatty acid tails are non- polar and they repel polar molecules

Question 22

how do specific molecules pass through membrane using proteins

Answer 22

channel and carrier proteins are a specific shape because of their unique tertiary structure so they only transport specific molecules that are complementary to the binding site

Question 23

what does it mean when in a graph for rate of facilitated diffusion, the graph levels

Answer 23

because all carrier proteins are saturated/binding site is full

number of carrier proteins can become a limiting factor

Question 24

what is osmosis

Answer 24

net movement of water particles from a higher water potential to a lower water potential through a selectively permeable membrane

Question 25

what is water potential ( kPa )

Answer 25

pressure exerted by free water molecules whilst moving and colliding

more free moving water = more pressure = higher water potential

Question 26

what does adding a solute do to the water potential

Answer 26

lowers it , makes solution negative

Question 27

what is an isotonic solution

Answer 27

2 solutions with same water potential

Question 28

what is an hypotonic and hypertonic solution

Answer 28

hypotonic - has lower water potential

hypertonic solution - has higher water potential

Question 29

what is active transport used for

Answer 29

transport molecules across the membrane against their concentration gradient, from lower concentration to higher concentration

Question 30

why does active transport only use carrier proteins

Answer 30

because it requires a specifically shaped carrier protein with a complementary binding site, that only complementary molecules bind to

Question 31

where is the energy for active transport come from and what is it used for

Answer 31

hydrolysis of atp which is produced during respiration

and is used to change shape of carrier protein (by phosphorylation)

the change in protein shape transports the molecule across the membrane into an area where the concentration of the molecule is relatively high

Question 32

give types of bulk transport

Answer 32

exocytosis and endocytosis

Question 33

give one use of exocytosis

Answer 33

move enzymes and glycoproteins from the golgi apparatus to the cell membrane to secrete proteins

Question 34

what is needed for exocytosis

Answer 34

atp required to move vesicles to cell surface membrane and the vesicles fuse with the membrane

atp also needed for endocytosis

Question 35

what molecules are transported by active transport

Answer 35

ions and glucose

Question 36

what happens if aerobic respiration is inhibited

Answer 36

Active transport can’t occur as there is no/less ATP. All the other types of transport can still continue until equilibrium is reached.

Question 37

What happens if the tertiary structure of the carrier protein changes?

Answer 37

Facilitated diffusion/active transport can’t occur (because the binding site has changed shape and is no longer complementary to the molecule, therefore they will not fit/bind).