transport across membranes

Question 1

give 2 similarities in the movement of substances by diffusion and osmosis (2)

Answer 1

• neither use ATP
• down a concentration gradient

Question 2

scientist placed cells in solution with higher water potential than cytoplasm, how did this move the chromosomes further apart (2)

Answer 2

• water molecules entered cell by osmosis
• cytoplasm got bigger due to increase in water

Question 3

how would a student investigate effect of surface area on osmosis in potato cubes- start after cubes have been cut (3)

Answer 3

1. Ensure all cut surfaces of the eight
   cubes are exposed to the sucrose solution- place each in boiling tube
2. control temperature with thermostatically controlled water bath
3. dry cubes before measuring by blotting with paper towel
4. Measure mass of cubes with balance every 20 minutes

Question 4

student produced different concentrations from a concentrated sucrose solution, name this method (1)

Answer 4

dilution series

Question 5

suggest two reasons why both carbon dioxide and water can pass through aquaporins (2)

Answer 5

• they are similar shapes
• they are both small (can fit through channel proteins)

Question 6

in this osmosis investigation the strawberries were cut into slices- explain advantage of this (2)

Answer 6

• increases surface area
• increases rate of osmosis

Question 7

the scientists blotted the strawberries dry before weighing them- why? (2)

Answer 7

• sucrose solution would add to the mass
• the mass would vary every time

Question 8

name and describe 5 ways substances can move across the cell-surface membrane into a cell (5)

Answer 8

1. simple diffusion of small and non-polar molecules DOWN a concentration gradient
2. facilitated diffusion down concentration gradient via protein carrier
3. osmosis of water down water potential gradient
4. active transport against concentration gradient via protein carrier using ATP
5. co-transport of 2 different substances using a carrier protein

Question 9

explain the function of ATP hydrolase (2)

Answer 9

1. (ATP to ADP + Pi) Releases energy
2. energy allows ions to be moved against a concentration gradient

Question 10

the movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum- how? (2)

Answer 10

1. maintains a concentration gradient for Na+ from ileum into cell
2. Na+ moving in by facilitated diffusion brings glucose with it

Question 11

Describe and explain 3 features you would expect to find in a cell specialised for absorption (3)

Answer 11

1. folded membrane/ microvilli so large surface area
2. large number of carrier proteins so fast rate of absorption
3. large number of mitochondria so make more ATP for respiration

Question 12

the movement of substances across cell membranes is affected by membrane structure, describe how. (5)

Answer 12

1. phospholipid bilayer allows movement of non-polar substances
2. phospholipid bilayer prevents movement of polar substances
3. carrier proteins allow active transport
4. channel proteins allow facilitated diffusion
5. shape of channel determines which substances move
6. number of channels determines how much movement

Question 13

the graph shows that monoglycerides are lipid soluble molecules, suggest how (2)

Answer 13

rate of uptake is proportional

so lipid soluble molecules diffuse through

Question 14

student put beetroot discs into equal volumes of water- explain importance of controlling this variable. (2)

Answer 14

-if too much water, concentration of pigment will be lower, solution is lighter

• so results from different temperatures are comparable

Question 15

Describe a method the student could use to monitor temperature in each test tube (1)

Answer 15

Take readings using a themometer

Question 16

suggest how the increase in temperature of water caused the release of the red pigment (3)

Answer 16

• damage to cell surface membrane
• membrane proteins denature
• increased fluidity

Question 17

suggest and explain 3 ways the cell-surface membrane of cells lining the uterus may be adapted to allow rapid transport of nutrients (3)

Answer 17

1. membrane folded so increased surface area
2. large number of protein channels for facilitated diffusion
3. large number of protein carriers for active transport

Question 18

sodium ions from sodium chloride are absorbed by cells lining the gut, some of these have a carrier protein NHE3- this actively transports 1 Na ion into cell in exchange for 1 proton(H ion) out of the cell
suggest how NHE3 does this (3)

Answer 18

• co transport
• uses hydrolysis of ATP
• sodium ion and proton bind to the protein
• protein changes shape to move sodium ion and proton across membrane

Question 19

high absorption of salt can result in higher than normal concentration of salt in blood plasma entering capillaries- explain how this leads to a build up of tissue fluid (4)

Answer 19

1. higher salt means lower water potential of tissue fluid
2. less water returns to capillary by osmosis
3. results in higher blood pressure
4. so more fluid pushed out at arteriole end of capillary

Question 20

compare and contrast the processes by which water and inorganic ions enter cells (3)

Answer 20

• both move down concentration gradient
• both move through protein channels in membrane
• ions can move against a concentration gradient by active transport, water cannot.

Question 21

contrast the process of facilitated diffusion and active transport (3)

Answer 21

1. FD involves channel or carrier proteins but active transport only involves carrier proteins
2. FD does not use ATP whereas active transport uses ATP
3. FD is down a concentration gradient whereas active transport is against a concentration gradient

Question 22

describe the mechanism for the absorption of amino acids in the ileum (4)

Answer 22

• facilitated diffusion of amino acids
• co-transport
• sodium ions actively transported from cell to blood
  -creates sodium ion concentration gradient

Question 23

describe how proteins are arranged in a plasma membrane and the part they play in transporting substances into/ out of cells (6)

Answer 23

• involved in facilitated diffusion
• involved in active transport
• proteins act as carriers
• carrier changes shape
• proteins form channels
• protein allows passage of water soluble molecules

Question 24

describe the structure of a cell membrane (5)

Answer 24

• bilayer of phospholipid molecules
• protein molecules passing through
• some with channels
• fatty acid tails inwards, hydrophilic head outwards
• proteins on surface

Question 25

explain why the diffusion of chloride ions involves a membrane protein and the diffusion of oxygen does not (5)

Answer 25

• Cl ions are polar
• cannot cross bilayer
• Cl ions transported by facilitated diffusion
• oxygen is non-polar
• can diffuse across bilayer

Question 26

the movement of substances across a cell membrane is affected by membrane structure. describe how (5)

Answer 26

-phospholipid bilayer allows diffusion of non polar substances

• Phospholipid bilayer prevents diffusion of polar substances
• carrier proteins allow active transport
• carrier proteins allow facilitated diffusion
• shape of carrier protein determines which substances are transported

-number of carrier proteins determine how much movement