BM - Lipids

Question 1

What are lipids, and what are their general properties?

Answer 1

Lipids are a group of biological molecules that are insoluble in water but soluble in organic solvents. They include triglycerides, phospholipids, and cholesterol

Question 2

What are triglycerides made of?

Answer 2

Triglycerides are composed of one glycerol molecule and three fatty acids, joined by ester bonds formed in condensation reactions.

Question 3

What is the difference between saturated and unsaturated fatty acids?

Answer 3

Saturated fatty acids have no double bonds between carbon atoms in their hydrocarbon chains, while unsaturated fatty acids have one or more double bonds, causing kinks in the chain.

Question 4

How are ester bonds formed in lipids?

Answer 4

Ester bonds are formed during a condensation reaction between the hydroxyl group of glycerol and the carboxyl group of a fatty acid, releasing a molecule of water.

Question 5

What is the structure of a phospholipid?

Answer 5

A phospholipid consists of one glycerol molecule, two fatty acids, and a phosphate group. The phosphate group is hydrophilic, while the fatty acid tails are hydrophobic.

Question 6

Why are phospholipids important in biological membranes?

Answer 6

Phospholipids form a bilayer in biological membranes, with hydrophilic heads facing outward and hydrophobic tails facing inward, creating a barrier that controls the passage of substances.

Question 7

What is the test for lipids, and how is it performed?

Answer 7

The emulsion test is used to test for lipids. Mix the sample with ethanol, then add water. A white, milky emulsion indicates the presence of lipids.

Question 8

What are the roles of lipids in organisms?

Answer 8

Lipids serve as energy storage, provide insulation, protect organs, form cellular membranes, and act as signaling molecules (e.g., hormones).

Question 9

How do the properties of triglycerides relate to their function?

Answer 9

Triglycerides are energy-rich due to their high proportion of carbon-hydrogen bonds. They are insoluble, so they do not affect water potential, and they provide insulation and protection.

Question 10

What makes cholesterol important in biological membranes?

Answer 10

Cholesterol fits between phospholipid molecules in the bilayer, providing membrane stability and fluidity.

Question 11

The general structure of a fatty acid is RCOOH.
Name the group represented by COOH

Answer 11

(a) Carboxyl;

Question 12

Describe how you would test for the presence of a lipid in a liquid sample of food.

2 marks

Answer 12

1. Add ethanol/alcohol then add water and shake/mix
2. White/milky (emulsion)

Question 13

Describe how a triglyceride molecule is formed.

3 marks

Answer 13

1. One glycerol and three fatty acids;
2. Condensation (reactions) and removal of three molecules of water;
3. Ester bond(s) (formed);

Question 14

Describe how an ester bond is formed in a phospholipid molecule.

2 marks

Answer 14

1. Condensation (reaction) by Loss of water;
2. Between of glycerol and fatty acid;

Question 15

what is the bond between a glycerol and fatty acid molecule in a triglyceride.

Answer 15

Ester (bond)

Question 16

Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum.

Answer 16

Red blood cells free in blood / not supported by other cells so cholesterol helps to maintain shape;

Question 17

E. coli has no cholesterol in its cell-surface membrane. Despite this, the cell maintains a constant shape. Explain why.

2 marks

Answer 17

1. Cell unable to change shape;
2. (Because) cell has a cell wall;
3. (Wall is) rigid / made of peptidoglycan / murein

Question 18

The structure of a phospholipid molecule is different from that of a triglyceride.
Describe how a phospholipid is different.

Answer 18

1. Phosphate / PO4;
2. Instead of one of the fatty acids / and two fatty acids;

Question 19

what is meant by an unsaturated fatty acid.

Answer 19

double bonds between 2 carbon atoms

Question 20

Hydrogen bonds are important in cellulose molecules. Explain why.

2 marks

Answer 20

1. Holds chains forms microfibrils that provide strength / rigidity (to cellulose / cell wall);
2. Hydrogen bonds strong in large numbers

Question 21

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells

Answer 21

• compact so its tigtly packed and doesn’t take space

Question 22

Explain two ways in which fatty acids are important in
the formation of new cells.

4 marks

Answer 22

• Fatty acids used to make phospholipids in membranes;
• Fatty acids respired to release energy;
• More triglycerides more energy released;