3.1.3 Lipids

Question 1

What are the two types of lipids? (2)

Answer 1

• Triglycerides
• Phospholipids

Question 2

Why are lipids not considered polymers? (1)

Answer 2

• They are not made from a small repeating unit (monomer)
• They are macromolecules (made of two or more different molecules)

Question 3

Describe how triglycerides are formed (3)

Answer 3

• 3 fatty acids combine to one glycerol molecule during a condensation reaction
• With the loss of three water molecules
• And the formation of an ester bond

Question 4

What type of bond does a condensation reaction between glycerol and a fatty acid (RCOOH) form? (1)

Answer 4

Ester bond

Question 5

What is the difference between a saturated and unsaturated molecule? (2)

Answer 5

• Saturated = no double bonds between the carbon atoms
• Unsaturated = contains one or more carbon to carbon double bond

Question 6

Describe how a phospholipid is formed (3)

Answer 6

• One glycerol, two fatty acids and a phosphate group
• Joined together by an ester bond
• During a condensation reaction

Question 7

Describe the structure of a phospholipid molecule (2)

Answer 7

• Has a polar hydrophilic head containing the phosphate group
• Non-polar hydrophobic tail consisting of long fatty acid chains

Question 8

What is the characteristic of the hydrophilic head of a phospholipid? (2)

Answer 8

• Polar
• So attracts water

Question 9

What is the characteristic of the hydrophobic tail of a phospholipid? (2)

Answer 9

• Non-polar
• So repels water

Question 10

How do phospholipid molecules arrange themselves in a bilayer? (3)

Answer 10

• Form a bilayer
• With the hydrophobic tails attracted to each other and away from water
• While the hydrophilic heads face outward towards the water

Question 11

What is the function of the phospholipid bilayer in cell membranes? (1)

Answer 11

Enables lipid soluble molecules to pass quickly through cell membranes

Question 12

What are two methods that you could use to carry out the hydrolysis of lipids? (2)

Answer 12

• Heat with acid or alkali
• Use lipase at its optimum temperature and pH

Question 13

Describe the adaptations of triglycerides for their functions (6)

Answer 13

• Possess a high proportion of C-H bonds
• So will release twice as much energy as carbohydrates during aerobic respiration
• High ratio of hydrogen to oxygen atoms
• Which releases water when respired, important for organisms living in dry desserts
• Non-polar and therefore, insoluble
• Ideal as a storage compound as they are osmotically inactive

Question 14

What are the similarities between triglycerides and phospholipids? (4)

Answer 14

• Both have glycerol backbone
• Both contain ester bonds
• Both contain the elements C, H, O.
• Both formed by condensation reactions

Question 15

What are the differences between triglycerides and phospholipids? (3)

Answer 15

• Phospholipids contain two fatty acids whereas, triglycerides contain 3 fatty acids
• Phospholipids contain one phosphate group whereas, triglycerides do not contain a phosphate group
• Phospholipids have a hydrophilic head and a hydrophobic tail whereas, triglycerides are hydrophobic