1.5- Lipids

Question 1

What are some of the characteristics of lipids?

Answer 1

Contain carbon,oxygen and hydrogen
Insoluable in water
Soluable in organic solvents
The proportion of oxygen to carbon and hydrogen is lower than in carbohydrates

Question 2

How do lipids act as a source of energy?

Answer 2

Oxidised to release energy

Question 3

How do lipids provide waterproofing?

Answer 3

Insoluable in water

Question 4

How do lipids provide insulation?

Answer 4

Slow conductors of heat and when stored below the body surface they help to retain heat

Question 5

Describe the structure and formation of a triglyceride

Answer 5

1 glycerol molecule and three fatty acid molecules (hydrocarbon tails)
Each fatty acid forms an ester bond with glycerol through a condensation reaction

Question 6

How does the structure of triglycerides relate to their function?

Answer 6

1. Low mass to energy ratio-good storage molecules because energy can be stored in a small volume
2. Large non polar molecules which are insoluble in water- doesn’t affect water potential of cells or osmosis
3. High ratio of hydrogen to oxygen atoms-when oxidised they release water providing an important source of water especially for organisms living in deserts
4. High ratio of carbon-hydrogen energy storing bonds-good source of energy

Question 7

Describe the structure of a phospholipid

Answer 7

Same as a triglyceride except that one of the fatty acid tails is replaced by a phosphate group
Hydrophilic head and hydrophobic tail

Question 8

How does the structure of a phospholipid relate to its function?

Answer 8

1.Hydrophilic head and the hydrophobic tail- in an aqueous environment they form a bilayer within cell-surface membranes. A hydrophobic barrier is formed between the inside and the outside of the cells.
2. Hydrophilic phosphate heads- help to hold at the surface of the cell-surface membrane
3. Phospholipid structure- allows them to form glycolipids by combining with carbohydrates within the cell surface membrane.

Question 9

Describe the test for lipids

Answer 9

1. Take 2cm3 of the sample being tested and add 5cm3 of ethanol
2. Shake the tube throughly to dissolve any lipid in the sample
3. Add 5cm3 water and shake gently
4. A milky-white emulsion represents the presence of a lipid
5. As a control repeat the method using water instead of the sample and it should remain clear