UNIT 2 (topic 3) transport across membranes

Question 1

explain the term simple diffusion

Answer 1

the net movement of random molecules down a concentration gradient from high to low concentration until reaching dynamic equilibrium

Question 2

what molecules can transport via simple diffusion

Answer 2

non-polar , hydrophobic, small, lipid soluble molecules

Question 3

how does temperature effect diffusion

Answer 3

rate increases as temperature increases - more kinetic energy so net movement increases

Question 4

how does the length of the pathway effect diffusion

Answer 4

rate decreases as length increases - longer the pathway, longer it takes to travel

Question 5

how does the concentration gradient effect diffusion

Answer 5

steeper gradient, faster the rate - more molecules need to diffuse to make dynamic equilibrium

Question 6

how does the surface area of the membrane effect the rate

Answer 6

rate increases as the surface are increases - more membrane = more molecules can diffuse at the same time

Question 7

why is facilitated diffusion used

Answer 7

molecules that are too big to pass through the fatty acids, polar, hydrophilic

Question 8

how are protein channels used in facilitated diffusion

Answer 8

forms a hydrophilic water channel that allow specific molecules to pass through the membrane

Question 9

how are carrier proteins used in facilitated diffusion

Answer 9

binds and changes shape of the molecule to allow it to pass through the membrane

Question 10

define the term ‘active transport’

Answer 10

moves substances against the concentration gradient using ATP - with a specific carrier protein

Question 11

explain the process of active transport

Answer 11

• molecules bind to carrier proteins and ATP attaches to the membrane protein
• phosphate molecules bind to the protein and breaks protein into ADP and phosphate group releasing energy and changing shape for access

Question 12

define the term ‘osmosis’

Answer 12

the passage of water from a region of high to low water potential through a partially permeable membrane

Question 13

define the term ‘water potential’

Answer 13

a measure of pressure exerted by the movement of water - the more water can move, the higher the water potential

Question 14

why does only 50% of glucose get absorbed in the digestive system

Answer 14

becomes dynamic equilibrium as there is no concentration gradient for diffusion to take place

Question 15

what is the function of microvilli

Answer 15

large surface area for absorption

Question 16

what is the reason for a single layered membrane

Answer 16

short diffusion pathway

Question 17

what is the reason for co-transport

Answer 17

allows a greater rate of uptake of polar molecules from digestion

Question 18

explain the steps of co-transport

Answer 18

• 3 Na+ ions transported out and 2K+ ions transported out - creates a concentration gradient for Na+
• Na+ moves into the cell down the concentration gradient via co-transport proteins - glucose enters with Na+ against concentration gradient
• glucose enters the blood down a concentration gradient via facilitated diffusion - carried away to be used for respiration

Question 19

define the term ‘endocytosis’

Answer 19

molecules entering the cell

Question 20

define the term ‘exocytosis’

Answer 20

molecules exiting the cell