Biological Molecules - 3.1.3 Lipids - Triglycerides, Phospholipids and the Emulsion Test

Question 1

Which 3 elements do lipids contain?

Answer 1

Carbon

Hydrogen

Oxygen

Question 2

Which part of a phospholipid is hydrophilic?

Answer 2

The phosphate ‘head’

Question 3

What does hydrophobic mean?

Answer 3

water hating

Question 4

How does the structure of triglycerides relate to their properties?

Answer 4

• High ratio of carbon-hydrogen bonds make them an excellent energy source
• Low mass to energy ratio- animals don’t have to carry a heavy energy store around.
• Non-polar molecules are insoluble in water so they do not affect osmosis in cells.
• High ratio of hydrogen to oxygen atoms so water released when trigylcerides are oxidised. Good for animals in deserts.

Question 5

What state do monounsaturated and polyunsaturated fats take at room temperature?

Answer 5

Liquid - they are oils.

Question 6

What is mean by a saturated fatty acid?

Answer 6

A fatty acid that contains no double bonds between the carbon atoms

Question 7

Phospholipids are p___________ molecules

Answer 7

polar

Question 8

What does the following describe:

• Add 2cm3 of food and add to a test tube.
• Add 5 cm3 of ethanol
• Shake the tube thoroughly to dissolve any lipid.
• Add 5cm3 of water and shake gently
• A cloudy-white colour indicates a positive result.

Answer 8

The emulsion test for lipids

Question 9

What state do saturated lipids take at room temperature?

Answer 9

Solid - they are fats

Question 10

What is meant by a polyunsaturated fatty acid?

Answer 10

A fatty acid that contains more than 1 double bond between its carbon atoms.

Question 11

What does hydrophilic mean?

Answer 11

attracted to water

Question 12

What type of bond forms between glycerol and fatty acid molecules?

Answer 12

Ester bond

Question 13

What type of reaction takes place when a fatty acid molecule is removed from a glycerol molecule?

Answer 13

Hydrolysis

Question 14

What type of reaction takes place when a glycerol molecule joins with a fatty acid molecule?

Answer 14

Condensation reaction

Question 15

Describe how you would carry out an emulsion test for lipids

Answer 15

The emulsion test for lipids:

• Add 2cm3 of food and add to a test tube.
• Add 5 cm3 of ethanol
• Shake the tube thoroughly to dissolve any lipid.
• Add 5cm3 of water and shake gently
• A cloudy-white colour indicates a positive result.

Question 16

Which part of a phospholipid is hydrophobic?

Answer 16

The fatty acid ‘tails’

Question 17

What decides the properties of different fats and oils?

Answer 17

Variations in their fatty acid chains

Question 18

List the roles of lipids in living organisms.

Answer 18

• Cell membranes
• Energy store
• Waterproofing
• Heat insulation
• Electrical insulation
• Protection of organs e.g. kidneys

Question 19

Why are triglycerides called triglycerides?

Answer 19

They contain 1 glycerol molecule (glyceride) and 3 fatty acids (tri)

Question 20

What is meant by a monounsaturated fatty acid?

Answer 20

A fatty acid that contains 1 double bond between 1 pair of its carbon atoms.

Question 21

Describe the structure of a phospholipid

Answer 21

1 glycerol molecule attached to

2 fatty acid molecules and

1 phosphate molecule

Question 22

How does the structure of phospholipids relate to their properties?

Answer 22

• Polar molecules - meaning that they can form a barrier (cell membrane) between water inside and outside a cell.
• The phospholipid can form glycolipids by combining with carbohydrates. These are important in cell recognition.

Question 23

Name the 2 main groups of lipid

Answer 23

Triglycerides (fats and oils)

Phospholipids

Question 24

What happens when a phospholipid is placed in water?

Answer 24

The hydrophilic head positions itself towards water.

The hydrophobic tail positions itself away from water

Question 25

List the characteristics shared by all lipids

Answer 25

• They contain: Carbon, Hydrogen and Oxygen
• Lower proportion of oxygen to carbon and hydrogen than carbohydrates.
• Insoluble in water
• Soluble in organic solvents e.g. alcohols

Question 26

how do you test for lipids?

Answer 26

dissolve in alcohol, then

add water then

white emulsion shows presence of lipid

Question 27

name the bond between the glycerol and the fatty acid chains in a lipid molecule

Answer 27

ester

Question 28

How can you tell the difference between a fatty acid that is saturated and how which is not?

Answer 28

saturated FA have no double bonds between carbon atoms

Question 29

what is the difference between a triglyceride and a phospholipid?

Answer 29

in a phospholipid, one FA is replaced with a phosphate

Question 30

name the reaction to breakdown phospholipids to release the phosphate

Answer 30

hydrolysis

Question 31

name the element found in all amino acids but not in triglycerides?

Answer 31

Nitrogen

Question 32

Compare and contrast structure of triglycerides and phospholipids

Answer 32

Both have ester bond

both contain glycerol

fatty acids on both can be saturated or unsaturated

Both contain C, H, O but phospholipids have also P

Triglycerides have 3 FA, Phospholipds have 2 FA and 1 phosphate group

Question 33

Compare and contrast the properties of triglycerides and phospholipids

Answer 33

Both insoluble in water

Triglycerides are hydrophobic/non polar but phospholipids have hydrophobic and hydrophillic (polar) regions

Phospholipids form a micelle bilayer but triglycerides dont