2A: gas exchange, cell membranes and transport

Question 1

why do cells need membranes (5)

Answer 1

• to control what substances enter and exit the cell
• compartmentalisation ( barrier between the organelles within the cytoplasm)
• contains reactions within the cell
• allows communication with the external environment
• allows chemical gradients to be created and used

Question 2

what are membranes made of

Answer 2

made of phospholipids

Question 3

why can other molecules and water soluble molecules not directly pass through membranes

Answer 3

the membranes inside layer is hydrophobic therefore they travel through pathways composed of proteins (channel proteins)
-some molecules are also too big to pass through therefore they also travel using these pathways

Question 4

how are the fats arranged in the membrane

Answer 4

in a bilyer

Question 5

what is included in the membrane

Answer 5

phospholipid bilayer, proteins, glycoproteins, glycolipids and cholesterol

Question 6

what are glycoproteins

Answer 6

a carbohydrate chain attatched to a protein

Question 7

what are glycolipids

Answer 7

a chain of polysaccharides attatched to a lipid

Question 8

what is the function of cholesterol in membranes

Answer 8

it bonds with the phospolipids and makes the membrane more rigid

Question 9

why can only small molecules pass through the membrane

Answer 9

it is partially permeable therefore only small molecules can move between the gaps in the phospholipids

Question 10

is the bilayer polar or non polar ? and what does this mean

Answer 10

non polar therefore only non polar substances can pass through

Question 11

what is a channel protein

Answer 11

a protein that allows specific molecules through the bilayer

Question 12

what is the difference between intrinsic and extrinsic proteins

Answer 12

intrinsic : span the whole width of the membrane
extrinsic : confided to the inner or outer surface of the membrane

Question 13

what are extrinsic proteins used for

Answer 13

can be used as receptors for incoming messages from external

Question 14

what is the function of intrinsic proteins

Answer 14

allows polar substances to pass through the bilayer using protein channels

Question 15

what is the function of extrinsic proteins

Answer 15

allow cells to communicate with one another

Question 16

what are extrinsic proteins (peripheral)

Answer 16

glycoproteins found on the cell surface

Question 17

what does cholesterol do in membranes

Answer 17

regulates the fluidity of membranes

Question 18

what is facilitated diffusion

Answer 18

when larger molecules diffuse through the membrane using carrier/channel proteins

Question 19

what is the structure of a phospholipid

Answer 19

a glycerol head, attached to a phosphate, wuth two fatty acid tails

Question 20

what makes the phospholipid bilayer hydrophillic

Answer 20

glycerol heads

Question 21

what makes the phospholipids bilayer hydrophobic

Answer 21

fatty acid tails

Question 22

why are phospholipids in a fluid mosaic structure

Answer 22

the phospholipids and proteins are constantly moving

Question 23

what do carrier proteins do

Answer 23

move large molecules into or out of the cell - down their concentration gradient

Question 24

what do carrier proteins transport

Answer 24

molecules

Question 25

how do carrier proteins transport molecules (3)

Answer 25

- active transport - passive transport ie diffusion - facilitated diffusion

Question 26

how to channel proteins transport molecules

Answer 26

passive

Question 27

what do channel proteins do

Answer 27

form pores in the membrane for charged particles to diffuse through

Question 28

why doesn't diffusion always allow organisms to absorb the substances they need

Answer 28

bc the substance is too big or the substance has an opposing charge to the organism

Question 29

what is required for active transport

Answer 29

ATP (energy molecule)

Question 30

how does temperature affect rate of diffusion

Answer 30

the higher the temperature, the higher the rate of diffusion and it happens quicker (more happens and in less time)

Question 31

how does surface area affect the rate of diffusion

Answer 31

the greater the surface area, more molecules that can diffuse at a time therefore less time - high efficiency

Question 32

how does diffusion distance affect the rate of diffusion

Answer 32

the shorter the distance, the quicker the molecules diffuse

Question 33

how does molecule size affect rathe of diffusion

Answer 33

the smaller the molecule the quicker it diffuses as larger molecules collide with small molecules whilst diffusing therefore they take longer

Question 34

how does concentration gradient affect the rate of diffusion

Answer 34

the steeper the concentration gradient, the higher the rate of diffusion

Question 35

what is bulk transport

Answer 35

the moving of large quantities in/ out of cells

Question 36

what happens during a bulk transport process

Answer 36

energy is used to form vesicles and to move vesicles around the cell - this vesicle is used to transport substance in and out of the cell via endocytosis or exocytosis

Question 37

what are some examples of substances that entre/enter the cell

Answer 37

hormones- insulin being released plant cells- vesicles carry materials to make cell wall phagocytes- engulfing pathogens

Question 38

what is endocytosis

Answer 38

when solid substances (sometimes whole organism) are taken into a cell through infolding of the surface membrane, forming a vesicle

Question 39

what is exocytosis

Answer 39

when vesicles and vacuoles move towards the surface membrane, fuse with it, and release their content outside of the cell (some substances will be inserted into the plasma membrane instead)

Question 40

what does hypotonic mean

Answer 40

when a solution has more water than solute (dilute solution)

Question 41

what does hypertonic mean

Answer 41

when a solution has more solute than water (concentrated solution)

Question 42

what does isotonic mean

Answer 42

an equal amount of water and solute within a solution

Question 43

what does turgid mean

Answer 43

a cell at full capacity and swollen due to high liquid content

Question 44

how does SA:V ratio affect an organism transport

Answer 44

organisms with a smaller SA:V ratio cannot rely solely on diffusion for transport of substances as it would take too long

Question 45

why can multicellular organisms nor rely on diffusion for transport of substances

Answer 45

they have cells that are too far away from exchange surfaces for diffusion to suffice

Question 46

how do you calculate SA:V?

Answer 46

SA- (side x side) x how many faces V- h x w x l to make it decimal- do SA/V

Question 47

what are features of a good exchange surface

Answer 47

- one cell thick - high blood supply - large surface area - moist lining - permeable - well ventilated

Question 48

what is the benefit of a exchange surface being one cell thick

Answer 48

short diffusion distance therefore more diffusion happens

Question 49

what is the benefit of a exchange surface having a high blood supply?

Answer 49

maintains a steep concentration gradient which facilitates oxygen (& CO2) delivery to tissues

Question 50

what is the benefit of a exchange surface having a large surface area

Answer 50

facilitates a high rate of exchange as more diffusion can happen at once

Question 51

what is the benefit of a exchange surface having a moist lining

Answer 51

allows gases to dissolve so that they can diffuse into the blood

Question 52

what is the benefit of a exchange surface being permeable

Answer 52

respiratory gases can pass through it

Question 53

what is the benefit of a exchange surface being well ventilated

Answer 53

efficient delivery of O2/CO2 to the surface