Lipids 3.1.3

Question 1

Are lipids soluble or insoluble in water

Answer 1

Insoluble

Question 2

Are lipids polar or nonpolar

Answer 2

Non-polar

Question 3

Describe four characteristics of lipids

Answer 3

*They contain carbon, hydrogen and oxygen
The proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates.
*They are insoluble in water
*They are soluble in organic solvents E.G. acetone, alcohols.

Question 4

Name the four roles of lipids

Answer 4

Source of energy
Waterproofing
Insulation
Protection

Question 5

How do lipids provide a source of energy

Answer 5

When oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water (metabolic water).

Question 6

How to lipids waterproof

Answer 6

As lipids are insoluble in water, it is therefore useful for waterproofing, E.G. both plants and insects have waxy cuticles is that reduce water loss (conserving it), while the mammals produce an oily secretion from the sebaceous glands in the skin

Question 7

How do lipids provide insulation

Answer 7

Facts are slow conductors of heat and when stored beneath the body surface, help to retain body heat. They also act as electrical insulators E.G.the myelin sheath around nerve cells

Question 8

How do lipids provide protection

Answer 8

Fat is often stored around delicate organs, E.G.kidneys.

Question 9

How is a triglyceride molecule formed

Answer 9

It is formed by three condensation reactions between the three hydroxyl groups in the glycerol and the three fatty acid chains. This creates a triglyceride and three water molecules

Question 10

How do triglycerides differ from one another

Answer 10

The glycerol molecule stays the same in all triglycerides. The differences in the properties of the different facts and oils come from variations in the fatty acids

Question 11

What part of the fatty acid chains are polar and which are non polar

Answer 11

The hydrocarbon chains are nonpolar, but the carboxyl groups are polar.

Question 12

Define mono-unsaturated fatty acid

Answer 12

If it has one single double carbon bond

Question 13

Define Polyunsaturated fatty acid

Answer 13

If it has more than one double carbon bond

Question 14

How is the structure of triglycerides related to its properties

Answer 14

• Triglycerides have a high ratio of energy store and carbon hydrogen bonds to carbon atoms, so are an excellent source of energy.
• Triglycerides have a low mass to energy ratio, making them good storage molecules because lots of energy can be stored in a small volume. This is extremely beneficial to animals as it reduces the mass they have to carry around.
• Being larger, nonpolar molecules, triglycerides are insoluble in water, so they do not affect the water potential or osmosis in cells.
• As they have a high ratio of hydrogen to oxygen atoms, they release water and oxidised and therefore provide an important source of water, especially for organisms living in dry deserts e.g. camels

Question 15

What is a phospholipid

Answer 15

The phospholipid molecule is an ester composed of glycerol, two fatty acid chains and a polar group containing a phosphate group

Question 16

What part of the phospholipid are hydrophilic and what parts are hydrophobic

Answer 16

The phosphate group is hydrophilic and soluble in water, but the fatty acid chains are hydrophobic and are not soluble in water. At air-water, or oil-water interfaces, the phospholipid molecule orientate themselves so that their heads are in water.

Question 17

How does the phospholipid orientate itself in water

Answer 17

The hydrophilic heads are as close to the ward as possible and the hydrophilic tails are as far away from the water as possible

Question 18

How does the structure of a phospholipid relate to its properties

Answer 18

• Phospholipids are polar molecules, having hydrophilic phospholipid head and hydrophobic tails of two fatty acids. This means that in an aqueous environment, phospholipid molecules from a bilayer within cell surface membranes. As a result, a hydrophobic barrier is formed between the inside and the outside of the cell.
• The hydrophilic phospholipid heads of the phospholipid molecules help to hold at the cell-surface membrane.
• The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane. These are important in cell recognition.

Question 19

Name 5 differences between a triglycerides and phospholipids

Answer 19

*Triglycerides are lipids that are composed of a glycerol backbone attached to three fatty acid chains
Phospholipids are lipids composed of a phosphate group attached to a glycerol backbone
*Triglycerides have three fatty acid chains whereas phospholipids have three fatty acid chains
*Triglycerides have no phosphate group attached to the glycerol backbone whereas phospholipid have a phosphate group attached to the glycerol backbone
*In the formation of a triglyceride molecule, three water molecules are released whereas in the formation of a phospholipid molecule, to water molecules are released.
*Triglycerides act as fat storage in the body whereas phospholipid make up membranes in the cell.

Question 20

Test for lipids (emulsion test)

Answer 20

1) Take a completely dry and grease-free test tube
2) Grind 2 cm³ of the sample and add 5 cm³ of ethanol
3) shake the tube starrily to dissolve any lipid in the sample
4) Add 5 cm³ of water and shake gently
5) A cloudy white colour indicates the presence of a lipid
6) As a control, repeat the method using water instead of the sample, the final solution should remain clear.