transport across membranes

Question 1

name 5 ways substances can be transported across a membrane

Answer 1

simple diffusion
facilitated diffusion
osmosis
active transport
co transport

Question 2

define diffusion

Answer 2

Net movement of molecules or ions from an area of higher concentration to area of lower concentration

Question 3

define facilitated diffusion

Answer 3

diffusion of molecules via a carrier protein or channel protein down a concentration gradient

Question 4

define osmosis

Answer 4

net movement of water molecules from an area of higher water potential to an area of lower water potential across a selectively permeable membrane

Question 5

define active transport

Answer 5

Movement of molecules/ions from an area of lower concentration to an area of higher concentration using energy from ATP and carrier molecules

Question 6

Describe the phospholipids arrangement in a plasma membrane

Answer 6

Bilayer
Hydrophobic tails to inside
Hydrophilic heads to outside

Question 7

what are the functions of the phospholipid bilayer?(3)

Answer 7

allow lipid soluble molecules to enter and exit

prevent polar/ water soluble molecules

make membrane flexible and self sealing

Question 8

what are structures of a cell membrane?

Answer 8

phospholipid bilayer
transmembrane proteins
glycoproteins
glycolipids
cholesterol

Question 9

what are the functions of phospholipids in a cell membrane?(3)

Answer 9

allow lipid soluble molecules to enter

prevent water soluble molecules

make membrane flexible and self sealing

Question 10

describe the structure of a channel protein

Answer 10

form a water filled hydrophilic channel that is highly selective

Question 11

describe the structure of a carrier protein

Answer 11

has a binding site for a specific molecule

changes shape in response to binding target molecule

Question 12

what 4 things affect rate of diffusion?

Answer 12

temperature
size of concentration gradient
surface area of exchange surface
length of diffusion pathway

Question 13

how does a sodium potassium pump work? (4)

Answer 13

3 sodium ions and 1 ATP bind

ATP hydrolyses into ADP and a Pi stays bound. This provides energy to change shape

sodium ions released to other side, 2 potassium ions bind

Pi unbinds, reverting channel back to original position and releasing potassium ions

Question 14

describe how glucose is absorbed in the ileum

Answer 14

1. sodium ions are actively transported out of epithelial cells by sodium-potassium pump
2. this maintains higher conc gradient of Na+ in lumen

3.Na+ diffuses into epithelial cell cell carrying glucose molecules with it.

4. high conc of glucose in epithelial cell compared to blood so glucose diffuses into blood by facilitated diffusion.