Transport Across Cell Membranes

Question 1

What are the basic structure of cell membranes the same as

Answer 1

The cell surface membranes and the membrane around the cell organelle is the same

Question 2

What is a cell membrane made Up of(what it forms)

Answer 2

-phospholipid bilayer

Question 3

Why is a cell membrane arranged in a phospholipid bilayer

Answer 3

• fatty acids form a hydrophobic layer between the hydrophilic phosphate heads
  -various proteins in bilayer
  -carbohydrates attached some glycolipids and glycoproteins

Question 4

Describe the fluid mosaic model

Answer 4

-fluid: phospholipid move constantly
- mosaic:proteins dotted between the phospholipids are of various shapes sizes

Question 5

What is the arrangement of phospholipid and proteins known as?

Answer 5

Fluid mosaic model

Question 6

What at the cell membrane components

Answer 6

-phospholipid
-intrinsic proteins
-extrinsic proteins
-glycoproteins
-glycolipids
-cholesterol may be presented

Question 7

Function of cholesterol in cell membrane

Answer 7

-it restricts movement of other molecules in membrane and phospholipids
-making it less fluid,provides mechanical stability, prevents water and dissolved ions leaking out
-bind to hydrophobic tails making them closely packed

Question 8

What is the function of extrinsic proteins

Answer 8

• Found on surface of membrane or embedded in one layer of membrane
• provide mechanical support
  -connect to proteins and lipids to make glycolipids and glycoproteins
  So they act as cell receptors for cell recognition of hormones and other molecules

Question 9

What is the function of intrinsic proteins

Answer 9

• They are carrier proteins or channel proteins
  -span bilayer
• involved in the transport of molecules across the membrane

Question 10

What is the difference between channel proteins and carrier proteins

Answer 10

Protein channel forms tubes that fill with water to enable water soluble ions to diffuse whereas carrier proteins bind to larger molecules and change the shape of them to transport them across membrane

Question 11

Function of phospholipid in cell membrane

Answer 11

• Form basic structure ofbilayer which’s partially permeable
• make membrane flexible
• prevent the a passage of water soluble molecules and allow lipid-soluble

Question 12

Function of glycoproteins in cell membrane

Answer 12

• Are receptors for chemical signals
• act as receptors for toxins and drugs

Question 13

Function of glycolipids in cell membrane

Answer 13

Role in cell recognition acting as cell markers or antigens

Question 14

What does it mean that the cell membrane is partially permable

Answer 14

Only lipid soluble molecules can pass through membrane via Simple diffusion

Question 15

What is simple diffusion

Answer 15

The net movement of molecules from an area of high concentration to low concentration
- passive random process that uses kinetic energy
-No ATP
- no proteins needed

Question 16

What are examples that use simple diffusion

Answer 16

-lipid soluble molecules
-CO2
O2

Question 17

What is the difference between facilitated diffusion and simple

Answer 17

Facilitated allows large water soluble molecules and ions to pass through the phospholipid bilayer which require channel proteins and carrier proteins

Question 18

Facilitated diffusion uses channel proteins what do they do?

Answer 18

• They form pores In the membrane for specific charged particles or ions to diffuse through
• down concentration gradient

Question 19

Define osmosis

Answer 19

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

Question 20

What is water potential

Answer 20

Pressure created by water molecules and is measured in kPa
-pure water has water potential of 0 so when more solutes are dissolved, in it the water potential will become more negative

Question 21

What does it suggest the more negative the water potential

Answer 21

The more solutes must be dissolved in it

Question 22

What is it meant by isotonic solution

Answer 22

Water potential is the same in the solution and the cell within the solution

Question 23

What is it meant by hypotonic solution

Answer 23

Water potential of a solution is more positive then
The cell
So lower solute concentration

Question 24

What is hypertonic solution

Answer 24

Water potential is more negative In solution then the cell

Question 25

What happens when animal cells are placed in a hypotonic solution

Answer 25

A lot of water will move into the cell by osmosis
Animal cells: no cell wall- pressure will cause cell wall to burst
Plants: become turgid

Question 26

What happens when animal and plant cells are placed in hypertonic solution

Answer 26

Both will shrink and become shrivelled due to large volumes of water leaving the cell due to osmosis

Question 27

Define active transport

Answer 27

The movement of substances from an area of lower concentration to higher concentration against a concentration gradient using ATP and carrier proteins

Question 28

What do the carrier proteins do in active transport

Answer 28

• certain large molecules binds to receptor site on carrier protein to go across membrane
  -ATP binds to protein and is hydrolysed to ADP and Pi so energy is used to change protein shape and open towards the inside of membrane
  -causes molecules to be carried against a concentration gradient
• Pi is released so protein reverts back to original shape

Question 29

What is co transport

Answer 29

Special type of facilitated diffusion
-carried out by co transporter proteins which enable diffusion of larger molecules accompanied by ion

Question 30

Describe co transport of glucose and sodium ions in the ileum

Answer 30

-sodium ions are transported out epithelial cell into the blood by co transport
-this reduce the sodium ion concentration in epithelial cell
-sodium ions can diffuse from lumen down their concentration gradient to epithelial cell
-sodium ions diffuse through co transporter proteins so glucose/ amino acids can be attached and transported to epithelial cell against concentration gradient
-glucose moves from epithelial cell to the blood by facilitated diffusion

Question 31

How can cells be adapted for rapid transport

Answer 31

-increase in surface area
-increase in the number of protein channels and carrier proteins in the membrane

Question 32

Facilitated diffusion uses carrier proteins what do they do

Answer 32

Large molecule attached to a carrier protein
Protein changes shape
It releases the molecule on the opposite side of the membrane