active transport

Question 1

define active transport

Answer 1

the movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration (ATP)

Question 2

what proteins does active transport require?

Answer 2

carrier proteins

Question 3

what provides the energy for active transport?

Answer 3

ATP

Question 4

explain how active transport works with a carrier protein

Answer 4

1. transport is through carrier proteins spanning the membrane
2. molecule binds to a receptor complementary in shape on the protein
3. ATP binds to the protein from the inside of the cell and is hydrolysed into ADP and Pi
4. this causes the carrier protein to change shape and release the molecule to the other side
5. the phosphate ion is then released and protein returns to its original shape

Question 4

what is active transport important in?

Answer 4

1. reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules
2. absorption of some products of digestion
3. loading sugar from the photosynthesising of cells in leaves into phloem for transport
4. loading inorganic ions from coil into root hairs

Question 4

what is co-transport?

Answer 4

the coupled movement of substances across a cell membrane via a carrier protein. It involves both facilitated diffusion and active transport

Question 5

explain the co-transport of sodium ions and glucose in the ileum

Answer 5

1. sodium ions are actively transported out of the epithelial cells into the blood by the S-P pump. This creates a conc gradient - there’s a higher conc of Na ions in the lumen of the ileum than the epi cell. K is pumped in. requires ATP
2. this causes sodium ions to diffuse into the epi cell from the lumen down their conc gradient. They do this via the S-G co-trans proteins. this carries glucose into the cell against its conc grad with Na, ‘’’ glucose conc in cell increases
3. glucose diffuses out of the cell into the blood own its conc gradient through a protein channel by facilitated diffusion. The blood carries it away which maintains the low conc

Question 5

what factors affect the rate of active transport?

Answer 5

1. the speed of individual carrier proteins- if they’re faster, the rate will be faster
2. the number of carrier proteins- more proteins means faster rate
3. the rate of respiration in the cell and the availability of ATP. If respiration is inhibited, active transport can’t take place

Question 6

what increases the surface area on epithelial cells for co-transporter proteins?

Answer 6

microvilli

Question 7

what is the ultimate aim of co-transport in the small intestine?

Answer 7

to get glucose into the bloodstream

Question 8

Name and describe five ways substances can move across the cell-surface membrane into a cell

Answer 8

1. diffusion of small/non-polar molecules down a concentration gradient
2. Facilitated diffusion down a concentration gradient via protein carrier/channel
3. Osmosis of water down a water potential gradient
4. Active transport against a 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 in co transport

Answer 9

(ATP to ADP + Pi ) Releases energy
(energy) allows ions to be moved against a concentration gradient/allows active transport of ions

Question 10

The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum. Explain how.

Answer 10

(Maintains/generates) a concentration/diffusion gradient for Na+ (from ileum into cell);
Na+ moving (in) by co-transport, brings glucose with it

Question 11

Describe and explain two features you would expect to find in a cell specialised for absorption

Answer 11

larger number of mitochondria for ATP
larger number of carrier proteins/co transporters
microvilli for large surface area