Cell membrane

Question 1

Why are cell membranes described as fluid mosaic?

Answer 1

• Bilayer is fluid bc phospholipid is constantly moving
• Proteins scattered through bilayer:
• Channel proteins/carrier proteins
• Receptor proteins detect chemicals that signal response from cell
• Glycoproteins - protein w/ polysaccharide chain
• Glycolipids - lipids w/ polysaccharide chain

Question 2

Describe the the structure + role of the phospholipid bilayer in the cell membrane

Answer 2

• Hydrophilic head
• Hydrophobic tail
• Head face outwards
• Centre of bilayer is hydrophobic so doesnt allow water soluble substances through

Question 3

Describe the the role of the cholesterol in the cell membrane

Answer 3

• Cholesterol is a lipid
• Fit btw phospholipid by binding to hydrophobic tail causing them to pack more closely, restricts movement of phospholipid making the membrane less fluid + more rigid
• Help maintain shape of animal cell

Question 4

Outline an experiment to test the permeability of a cell membrane

Answer 4

• Cut equal sized peices of beetroot, rinse to remove any pigment released during cutting
• Add to 5 diff test tube containing water
• Place test tubes in water bath at diff temp for same time
• Remove betroot leaving the coloured liquid
• Use colorimeter - higher absorbance, more pigment released, higher permeability

Question 5

Outline the results to test for the permeability of a cell membrane

Answer 5

• Below 0ºC - phospholipid don’t have much energy, packed closely together + mebrane is rigid. Channel proteins/carriers deform, inc permeability
• 0-45ºC - phospholipid can move + aren’t packed together tightly, membrane is partially permeable
• Above 45º - bilayer becomes more permeable, water inside cell expands putting pressure on membrane. Channel protein/carrier deform

Question 6

Describe simple diffusion

Answer 6

• Net movement of particles from an area of higher conc to an area of lower conc until equilibrium is reached
• Passive process

Question 7

Describe facilitated diffusion

Answer 7

• Diffusion using carrier proteins/channel proteins
• Passive process

Question 8

Describe how carrier proteins work

Answer 8

• Move large molecules across membrane
• Large molecule attaches to carrier protein in membrane
• Protein changes shape
• Releases molecule on opposite side of membrane

Question 9

Describe how channel proteins work

Answer 9

Form pores in membrane for charged particles to diffuse through

Question 10

Simple diffusion depends on..

Answer 10

• Conc gradient - higher
• Thickness of exchange surface - thinner
• Surface area - larger

Question 11

Facilitated diffusion depends on..

Answer 11

• Conc gradient - higher
• No. channel/carrier proteins - inc

Question 12

Define osmosis

Answer 12

Diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential

Question 13

Osmosis depends on..

Answer 13

• Water potential gradient - higher
• Thickness of exchange surface - thinner
• SA of exchange surface - larger

Question 14

How are carrier proteins different in active transport?

Answer 14

• Move from lower conc to higher conc
• Requires energy - ATP undergoes hydrolysis

Question 15

Outline the function of co-transporters in active transport

Answer 15

• Type of carrier protein
• Bind 2 molecules at a time
• Conc gradient of 1 used to move other against conc gradient

Question 16

Active transport depends on..

Answer 16

• Speed of individual proteins - faster
• No. carrier proteins - more
• Rate of respiration

Question 17

Outline the process of co-transport in the illeum

Answer 17

• Na⁺ actively transported out of illeum epithelial cell into blood by sodium potassium pump, creates conc gradient
• Na⁺ diffuse from lumen of ileum to epithelial cell down conc gradient via sodium glucose co-transporter protein
• Co-transporter carries glucose into cell w/ sodium, glucose conc inc inside cell
• Glucose diffuses into blood via. facilitated diffusion