3.1.3 Lipids

Question 1

State the characteristics of lipids

Answer 1

• Organic molecules
• Smaller than carbohydrates
• Insoluble in water
• Soluble in alcohol or acetone
• Solid at room temperature

Question 2

State the roles of lipids in an organism

Answer 2

1. Cell membranes and around organelles
2. Source of energy
3. Waterproofing
4. Insulation
5. Protection

Question 3

Explain the role of lipids in cell surface membranes and around organelles

Answer 3

Phospholipids contribute to flexibility and transfer of lipid soluble substances

Question 4

Explain the role of lipids in energy

Answer 4

When oxidises, provide twice the amount of energy as carbohydrates and release valuable water

Question 5

Explain the role of lipids in waterproofing

Answer 5

Insoluble in water

Question 6

Explain the role of lipids in insulation

Answer 6

Slow conductions of heat, so allow body heat to be maintained

Question 7

Explain the role of lipids in protection

Answer 7

Stored around delicate organs e.g., kidneys

Question 8

Draw and label a triglyceride

Answer 8

Should contain 3 fatty acids and a glycerol

Question 9

Which bond is found in triglycerides

Answer 9

Ester bonds

Question 10

When broken down, why do triglycerides change the pH of a solution

Answer 10

Because they contain a carboxyl group which is acidic in the hydrocarbon chain

Question 11

Unsaturated fats

Answer 11

Contain carbon to carbon double bond

Question 12

Saturated fats

Answer 12

Contain no carbon to carbon double bonds

Question 13

Which triglyceride has a kinked chain

Answer 13

Unsaturated triglyceride

Question 14

Explain the structure of triglycerides related to their properties (4)

Answer 14

• High ratio of energy storing carbon-hydrogen bonds - excellent source of energy
• Low mass to energy ratio - good storage molecules
• Large non-polar molecules - insoluble in water, so don’t affect water potential or osmosis
• High ratio of hydrogen to oxygen atoms - release important water when oxidised

Question 15

Draw and label the structure of a phospholipid

Answer 15

Should include, a phosphate, 2 fatty acids and a glycerol molecule

Question 16

Why are phospholipids able to form bilayers in water

Answer 16

• Hydrophobic head - interacts with water not fats
• Hydrophilic tail - interacts with fat, not water

Question 17

Why are phospholipids charged molecules

Answer 17

Phosphate group is a charged inorganic ion

Question 18

A student wants to test a solution for the presence of lipids

Describe a method he could use to do this.

                                                                                               **[4 marks]**

Answer 18

1. Emulsion test
2. (Dry and grease free test tube) add ethanol and shake
3. Add water and shake
4. Observe a cloudy/milky emulsion

Question 19

Compare and contrast the structure and properties of triglycerides and phospholipids. (5)

Answer 19

Similarities
- Both have ester bonds
- Both have fatty acids and glycerol
- Both insoluble in water
- Both only soluble in alcohol/acetone

Differences
- Triglycerides have 3 fatty acids, but phospholipids have 2 fatty acids
- Some triglycerides are saturated and unsaturated
- Phospholipids contain charged phosphate
- Triglycerides are completely hydrophobic, phospholipids are polar
- Phospholipids form bilayers

Ensure there is 2 similarities and 2 differences

Question 20

Phospholipids are _____________ molecules

Answer 20

Polar

Question 21

How do ester bonds form in a lipid

Answer 21

Condensation reaction between fatty acid and glycerol