3.1.3 Lipids

Question 1

Describe the similarities and differences between lipids and carbohydrates

Answer 1

• A similarity is that they both contain C,H,O atoms
• A difference is that lipids contain a higher proportion of C-H bonds compared to carbohydrates, therefore, more energy is released in lipids compared to carbohydrates.
• Carbohydrates are polymers, whereas lipids are not polymers because they aren’t made up of small repeating subunits

Question 2

What are the 2 classes of lipids

Answer 2

• Triglycerides
• Phospholipids

Question 3

Describe the structure of triglycerides

Answer 3

• triglycerides are made up of glycerol and 3 fatty acids that form ester bonds through a condensation reaction.

Question 4

Describe the difference between saturated, monounsaturated and polyunsaturated fatty acids

Answer 4

• saturated fatty acids have no double bonds between carbons in the hydrocarbon chain
• monounsaturated fatty acids have one double bond between carbons in the hydrocarbon chain
• polyunsaturated fatty acids have more than one double bond between carbons in the hydrocarbon chain

Question 5

Describe the function of triglycerides

Answer 5

• The function of triglycerides is that they are store energy, produce water, they are waterproof, they provide insulation, and protection.

Question 6

Explain why triglycerides can store energy

Answer 6

• Triglycerides store energy because they have a high proportion of C-H bonds, to C atoms, therefore they have a high energy:mass ratio. This means that a lot of energy can be stored in a small space.

Question 7

Explain why triglycerides can produce water

Answer 7

• Triglycerides produce water because they have a high ratio of H to O atoms, meaning that lipids can be oxidised to form water.

Question 8

Explain why triglycerides are waterproof

Answer 8

• triglycerides are waterproof because they have an even distribution of charge, meaning they are non-polar. This means that they cannot dissolve in polar substances like water, which have an uneven distribution of charge. Therefore, they’re hydrophobic.

Question 9

Describe the similarities and differences between triglycerides and phospholipids

Answer 9

• the similarities between triglycerides and phospholipids are that they both contain C, H, O, and glycerol.
• the differences between triglycerides and phospholipids are that phospholipids have 2 fatty acids, whereas triglycerides have 3.

Question 10

Describe the function of phospholipids

Answer 10

• the function of phospholipids is to form bilayers, which is a layer of 2 phospholipids. Bilayers make up surfaces in the body such as cell membranes.

Question 11

Describe the structure of phospholipids and its significance

Answer 11

• The tail is hydrophobic, whereas the head is hydrophilic, meaning it attracts water. This is why the head points towards the cytoplasm in the cell membrane.

Question 12

Cholesterol increases the stability of plasma membranes.
Cholesterol does this by making membranes less flexible. Red blood cells have more cholesterol in their membranes
than ileum cells. Suggest why

Answer 12

• Red blood cells move freely free in blood, therefore cholestrol helps maintain shape;

Question 13

Compare and contrast triglycerides and phospholipids

Answer 13

• Both contain glycerol
• Both consist of the elements C, H and O
• Both contain ester bonds
• Triglycerides contain three fatty acids, whereas PLs contain two fatty acids and one
  phosphate group
• Triglycerides are completely insoluble in water. On the other hand, phospholipids have a
  hydrophilic head which does interact with water. The hydrophobic tail is hydrophobic
  and is repelled by water
• Triglycerides are good energy storage molecules, whilst phospholipids have a
  structural function and are found in cell membranes