topic 2 - exchange across cell membrane - active transport

Question 1

what does active transport use energy to do

Answer 1

to move molecules and ions across membranes, usually against a concentration gradient

Question 2

how does active transport work

Answer 2

a molecule attaches to the carrier protein, the protein changes shape and this moves the molecule across the membrane, releasing it on the other side of

Question 3

what is active transport similar to

Answer 3

facilitated diffusion

Question 4

what are the two main differences between active transport and facilitated diffusion

Answer 4

(1) active transport usually moves solutes from a low to high concentration - in facilitated diffusion, they always move from a high to a low concentration
(2) active transport requires energy - facilitated diffusion does not

Question 5

how is ATP produced

Answer 5

by respiration

Question 6

how are solutes transported by ATP

Answer 6

ATP undergoes a hydrolysis reaction, splitting into ADP and Pi (inorganic phosphate) - this releases energy so that the solutes can be transported

Question 7

what are co-transporters a type of

Answer 7

carrier protein

Question 8

how many molecules do carrier proteins bind to at a time

Answer 8

two

Question 9

what is the concentration gradient of one of the molecules used to move

Answer 9

the other molecule against its own concentration gradient

Question 10

describe the co - transport of sodium ions and glucose

Answer 10

sodium ions move into the cell down their concentration gradient - this moves glucose into the cell too, against its concentration gradient

Question 11

what are three ways the rate of active transport is affected by

Answer 11

(1) the speed of individual carrier proteins - the faster they work, the faster the rate of active transport
(2) the number of carrier proteins present - the more proteins there are, the faster the rate of active transport
(3) the rate of respiration in the cell and the availability of ATP - if respiration is inhibited, active transport can’t take place

Question 12

what is glucose absorbed by and where

Answer 12

by co-transport in the mammalian ileum

Question 13

how is glucose absorbed in the mammalian ileum

Answer 13

glucose is absorbed into the bloodstream in the small intestine - in the ileum the concentration of glucose is too low for glucose to diffuse out into the blood - so glucose is absorbed from the lumen of the ileum by the co-transport

Question 14

what’s the first step of how glucose enters the ileum epithelium with sodium ions

Answer 14

sodium ions are actively transported out of the ileum epithelial cells, into the blood, by the sodium potassium pump - this creates a concentration gradient - there’s now a higher concentration of sodium ions in the lumen of the ileum than inside the cell

Question 15

what’s the second step of how glucose enters the ileum epithelium with sodium ions

Answer 15

this causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell, down their concentration gradient - they do this via the sodium-glucose co-transporter proteins

Question 16

what’s the third step of how glucose enters the ileum epithelium with sodium ions

Answer 16

the co-transporter carries glucose into the cell with the sodium - as a result the concentration of glucose inside the cell increases

Question 17

what’s the fourth step of how glucose enters the ileum epithelium with sodium ions

Answer 17

glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel by facilitated diffusion