Lipids (3.1.3)

Question 1

What are the elements present in lipids?

Answer 1

• Carbon
• Hydrogen
• Oxygen

Question 2

What does saturated and unsaturated mean?

Answer 2

• Saturated meaning no double bonds between the carbon atoms
• Unsaturated meaning one or more double bonds between the carbon atoms

Question 3

What happens in a condensation reaction between a glycerol and a fatty acid?

Answer 3

• An ester bond is formed

Question 4

How can lipids be hydrolysed into fatty acids and glycerol?

Answer 4

• Heating with an acid or an alkali
• Use of the enzyme lipase at its optimum temperature

Question 5

What does hydrophilic and hydrophobic mean?

Answer 5

• Hydrophilic means attracting water
• Hydrophobic means repelling water

Question 6

How are triglycerides formed?

Answer 6

• One glycerol and three fatty acids
• Condensations reactions and removal of three molecules of water
• Ester bonds formed

Question 7

What are the properties of triglycerides?

Answer 7

• Many carbon-hydrogen bonds → so releases twice the energy of carbohydrates during aerobic respiration
• High hydrogen to oxygen ratio → so releases water during aerobic respiration, vital for desert organisms
• Insoluble in water → so osmotically inactive, so does not affect water potential, making them ideal for energy storage

Question 8

What are phospholipids?

Answer 8

• Lipids containing a phosphate group
• They are composed of one glycerol molecule, two fatty acids and one phosphate group

Question 9

What is unique about phospholipids?

Answer 9

• They have a hydrophilic head continuing the phosphate group
• They have a hydrophobic tail consisting of the long fatty acid chains

Question 10

Describe the emulsion test and positive result for lipids

Answer 10

• Add ethanol
• Shake the mixture
• Add water to the mixture
• A white emulsion indicates lipid is present