Lipids + emulusion test + triglycerides

Question 1

Describe the emulsion test for lipids/ fats
(Include the outcome for a negative and positive test)

Answer 1

• take 2cm^3 of test sample and add about 5cm^3 of ethanol (ethanol is highly flammable)
• shake the test tube thoroughly to dissolve any liquid in the sample
• add 5cm^3 of water and shake gently

Negative test: clear
Positive test: forms a milky white emulsion

Question 2

State what forms triglycerides

Answer 2

One glycerol and three fatty acids

Question 3

Describe the process on how a triglyceride is formed

Answer 3

• triglycerides are formed by one glycerol and three fatty acids via a condensation reaction
• the OH group of each fatty acid is taken and bonds onto the hydrogen of the glycerol and are released as water
• the carbon atoms from each of the three fatty acids then bond onto the oxygen of the glycerol and forms 3 ester bonds
• a triglyceride is formed

Question 4

Describe the structure of saturated fatty acids and where it can be found

Answer 4

• every carbon is bonded to as many hydrogen atoms as possible - no more can be added, hence saturated (with hydrogen)
• carbon chain is straight with no kinks
• triglycerides of saturated fatty acids pack together to form solid fat at room temperature
• mainly found in animal fats from meat and dairy products

Question 5

Describe the structure of unsaturated fatty acids and where they can be found

Answer 5

• triglycerides consisting of ‘kinky’ unsaturated fatty acids do not pack easily together and form liquid oils at room temperature
• the more double bonds, the more kinks there will be
• not every carbon atom is bonded to as many hydrogen atoms as it could be, hence unsaturated (with hydrogen) and so there are double bonds present
• double bonds introduce a definite ‘kink’ in the carbon atom chain
• mainly found in vegetable oil, nuts and fish

Question 6

What is the function of triglycerides and how does their structure help them to carry out their function well?

Answer 6

Triglycerides are mainly used as energy storage molecules. They are good for this because:
- the long hydrocarbon tails of the fatty acids release loads of energy when they are broken down
- they are insoluble so they won’t affect the water potential of the cell
- they clamp together as insoluble droplets in cells