Chapter 4- Transport Across Cell Membranes

Question 1

Phospholipids within cell-surface membranes

Answer 1

-Form a bilayer -> hydrophilic heads pointing out + hydrophobic tails pointing in
Functions:
-Allow lipid-soluble substances to enter/leave
-Prevent water-soluble substances entering/leaving
-Flexibility

Question 2

Proteins within cell-surface membrane

Answer 2

-Some within bilayer + some span full bilayer
-Carrier proteins - bind to molecule + change shape so they can diffuse across
-Protein channels - form water-filled tubes so water-soluble ions can diffuse
Functions:
-transport of water
-a.transport through carrier proteins
-act as receptors + help cells adhere
-structural support

Question 3

Cholesterol within cell-surface membrane

Answer 3

-Very hydrophobic + within bilayer
Functions:
-reduce lateral movement of other molecules - pull fatty acid tails together
-decrease fluidity at high temps
-prevent leakage of water + dissolved ions

Question 4

Glycolipids in cell-surface membranes

Answer 4

-Carbohydrate + lipid
Functions:
-recognition sites
-maintain stability
-help cells attach -> tissue formation

Question 5

Glycoproteins within cell-surface membranes

Answer 5

-Carbohydrate attached to extrinsic proteins
Functions:
-recognition sites- so cells can recognise one another
-help cells attach

Question 6

Fluid-mosaic model of cell-surface membranes

Answer 6

-All molecules move = makes it flexible
-Mosaic = proteins vary in size/shape/pattern

Question 7

Diffusion definition

Answer 7

Net movement of molecules/ions from region of higher concentration to a region of lower concentration until evenly distributed

Question 8

Facilitated diffusion

Answer 8

-Movement of molecules such as charged ions + polar molecules
-Passive process - no ATP input
-Involves protein channels -> form water-filled channels
-Involves carrier proteins -> molecule is specific to protein + bind, shape changes, molecules released to inside

Question 9

Osmosis definition

Answer 9

Passage of water from a region of higher water potential to one of lower water potential through a selectively permeable membrane

Question 10

Until when do water molecules move in osmosis?

Answer 10

Until water potentials become equal - dynamic equilibrium (no net movement)

Question 11

Is osmosis a passive or active process?

Answer 11

Passive

Question 12

Active transport definition

Answer 12

Movement of molecules/ions into/out of a cell from a region of lower concentration to a region of higher concentration using ATP + carrier proteins

Question 13

How does active transport differ from passive forms?

Answer 13

-ATP needed
-against conc. gradient
-selective process
-uses carrier proteins

Question 14

Process of active transport

Answer 14

-Carrier proteins bind to molecule on one side (bind to receptor on carrier protein)
-Inside of cell -> ATP binds to protein -> splits into ADP + phosphate -> protein changes shape + opens on opposite side
-Molecule released to other side
-Phosphate released from protein which returns to original shape -> process can repeat (phosphate recombines with ADP)

Question 15

What is co-transport?

Answer 15

Method where glucose + amino acids are absorbed into blood along with sodium ions being transported by sodium-potassium pump

Question 16

How is the ileum adapted for co-transport?

Answer 16

-Epithelial cells contain microvilli -> increases S.A for carrier proteins
-Blood is constantly circulated - glucose is constantly removed - maintains conc. gradient

Question 17

Describe the process of co-transport

Answer 17

-Sodium ions out of epithelial cells by sodium-potassium pump into blood - takes place in carrier protein
-Higher conc. of sodium ions in the intestine lumen than in the epithelial cells
-Sodium ions diffuse into epithelial cells (down conc. gradient) through a co-transport protein + carry amino/acid glucose with them
-Amino acid/glucose pass into blood plasma (facilitated diffusion) using a carrier protein