1.5 - Lipids

Question 1

What 3 elements do lipids contain?

Answer 1

Carbon, Hydrogen and oxygen

Question 2

Is Oxygen more abundant in lipids or carbohydrates?

Answer 2

Oxygen is more abundant in Carbohydrates

Question 3

Are lipids soluble or insoluble?

Answer 3

Lipids are insoluble in water however soluble in organic solvents such as alcohols and acetones

Question 4

What are the two main groups of lipids?

Answer 4

Triglycerides and Phospholipids.

Question 5

Give 5 roles of Lipids.

Answer 5

1. Cell surface membrane
2. Source of energy
3. Waterproofing
4. Insulation
5. Protection

Question 6

How do phospholipids contribute contribute to cell membranes?

Answer 6

Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them.

Question 7

Why are lipids such a good Source of energy ?

Answer 7

When oxidised, lipids provide more than twice the energy as the same mass or carbohydrate and release valuable water.

Question 8

Why are lipids good for waterproofing?

Answer 8

Lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in the skin.

Question 9

Why are lipids such a good source of Insulation?

Answer 9

Fats are slow conductors or heat and when swred beneath the body surface help to retain body heat. They also act as electrical insulators in the myelin sheath around nerve cells.

Question 10

Why are lipids good for protection?

Answer 10

Fat is often stored around delicate organs, such as the kidney.

Question 11

What are triglycerides?

Answer 11

Triglycerides are so called because they have three (tri) fatty acids combined with glycerol (glyceride). Each fatty acid forms an ester bond with glycerol in a condensation reaction. Hydrolysis of a triglyceride therefore produces glycerol and three fatty acids.

Question 12

What part of a triglyceride is the same in all triglycerides?

Answer 12

the glycerol molecule in all triglycerides is the same, the differences in the properties of different fats and oils come from variations
in the fatty acids.

Question 13

What is a saturated triglyceride?

Answer 13

A triglyceride that contains no double bonds between carbon atoms in the fatty acid chains.

Question 14

What is a monounsaturated triglyceride?

Answer 14

A triglyceride that contains only one double bond between carbon atoms in the fatty acid chain.

Question 15

What is a polyunsaturated triglyceride?

Answer 15

A triglyceride that contains more than one double bond between carbon atoms in the fatty acid chains.

Question 16

How do double bonds affect triglycerides?

Answer 16

The double bonds cause the molecule to bend. They cannot therefore pack together so closely making them liquid at room temperature. i.e. they are oils.

Question 17

Why are triglycerides such an excellent store of energy?

Answer 17

Triglycerides have a high ratio of energy-storing carbon-hydrogen
bonds to carbon atoms and are therefore an excellent source of energy.

Question 18

Why are Triglycerides such a good storage molecule?

Answer 18

Triglycerides have low mass to energy ratio, making them good storage molecules because much energy can be stored in a small volume. This is especially beneficial to animals as it reduces the mass they have to carry as they move around.

Question 19

What is the benefit of triglycerides being large and non polar?

Answer 19

Being large, non-polar molecules, triglycerides are insoluble in water. As a result their storage does not affect osmosis in cells or the water potential of them.

Question 20

Why is having a high ratio of hydrogen to oxygen atoms a benefit in triglycerides?

Answer 20

As they have a high ratio of hydrogen to oxygen acorns, triglycerides release water when oxidised and therefore provide an important source of water, especially for organisms living in dry deserts.

Question 21

What are Phospholipids?

Answer 21

Phospholipids are similar to lipids except that one of the fatly acid molecules is replaced by a phosphate molecule

Question 22

What is the difference between phospholipids and triglycerides?

Answer 22

Whereas fatty acid molecules repel water (are hydrophobic), phosphate molecules attract water (are hydrophilic). A phospholipid is therefore made up of two parts:

1. A hydrophilic head
2. A hydrophobic tail

Question 23

What is Hydrophilic?

Answer 23

“water loving”

Question 24

What is Hydrophobic?

Answer 24

“water hating”

Question 25

How do phospholipids behave in water?

Answer 25

Phospholipids are polar molecules, having a hydrophilic phosphate head and a hydrophobic tail of two fatty acids. This means that in an aqueous environment, phospholipid molecules form a bilayer within cell-surface membranes. As a result, a hydrophobic barrier is formed between the inside and outside of a cell.

Question 26

How are glycolipids formed?

Answer 26

The phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These glycolipids are important in cell recognition.

Question 27

What is the test for lipids called?

Answer 27

The test for lipids is known as the emulsion test.

Question 28

Methodology for Emulsion test?

Answer 28

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

Question 29

Why is a cloudy emulsion produced?

Answer 29

The cloudy colour is due to any lipid in the sample being finely dispersed in the water to form an emulsion. Light passing through this emulsion is refracted as it passes from oil droplets to water droplets, making it appear cloudy.