1.5 Lipids

Question 1

roles of lipids:

Answer 1

• Insulation
• Protection
• Waxy cuticle
• Cell membrane
• Storage

Question 2

types of lipids:

Answer 2

• phospholipids
• triglycerides

Question 3

role of phospholipids:

Answer 3

cell membrane are made of them

Question 4

structure of a triglyceride:

Answer 4

Glycerol molecule
3x fatty acids (ester bonds to the glycerol)
-(releases 3x H2O)

Question 5

difference in saturated and unsaturated fatty acids:

Answer 5

unsaturated fatty acids have C=C bond (carbon carbon double bond)

Question 6

properties of triglycerides:

Answer 6

• high ratio of C-H bonds to C atoms = excellent source of energy
• insoluble in water (large, non-polar molecule) = doesn’t affect osmosis or water potential
• low mass to energy ratio = good storage molecule, energy can be stored in small volumes
• high ratio of H-O atoms = release water when oxidised, good source of water

Question 7

structure of phospholipids:

Answer 7

glycerol molecule
2x fatty acids (hydrophobic)
phosphate group, -ve charge, polar head (hydrophilic)

Question 8

formation of cell membrane bilayer:

Answer 8

the hydrophobic fatty acids face the middle
the phosphate head face away from each other
(phosphate heads may combine with CHO to form glycolipids for cell recognition)

Question 9

what does the cell membrane bilayer do?

Answer 9

it controls the movement of substances in and out of the cell

Question 10

Test for lipids:

Answer 10

• get a completely dry and grease-free test tube
• add sample and ethanol
  (for 2cm^3 of sample, add 5cm^3 of ethanol)
• mix well to ensure all lipids are broken down
• add water and shake gently

+ve result: cloudy-white emulsion
-ve result: clear