Lipids

Question 1

Lipids

Answer 1

Made up of atoms of carbon, hydrogen and oxygen
- They are insoluble in water
- Soluble in organic solvents e.g alcohols

Question 2

Triglycerides

Answer 2

Made up of glycerol and 3 fatty acids
- Each fatty acid forms an ester bond with a glycerol in a condensation reaction
- Good storage molecule
- Insoluble so don’t affect water potential of cells
- Lots of hydrogen and oxygen so they release water when oxidised - provide important source of water

Question 3

Saturated fatty acids

Answer 3

The hydrocarbon chain has no carbon-carbon double bonds

Question 4

Unsaturated fatty acids

Answer 4

The hydrocarbon chain has 1 or more carbon-carbon double bonds

Question 5

Phospholipids

Answer 5

Made up of glycerol, 2 fatty acids and a phosphate group
- Contains a hydrophilic head (phosphate group) which interacts with water
- And a hydrophobic tail (fatty acids) which repel water
- So molecules are polar - means that in aqueous environments they form a bilayer within cell-surface membranes
- Phospholipid structure allows them to form glycolipids with carbohydrates within cell-surface membrane - glycolipids are important in cell recognition

Question 6

Test for lipids

Answer 6

Emulsion test
1) Add 2cm3 of sample into test tube and add 5cm3 of ethanol
2) Shake test tube then add 5cm3 of water
3) Shake again
5) Milky white precipitate = positive result (lipid present)