Lipids

Question 1

Roles of lipids

Answer 1

Store of energy for producing ATP in respiration
Insulation (slow conductors of heat and electrical insulators in the myelin sheath)
Protection (stored around delicate organs)
Waterproofing e.g. waxy cuticles of leaves

Production of phospholipids for formation of cell surface/ organelle membranes

Question 2

Similarities and differences between saturated and unsaturated fatty acids

Answer 2

Saturated fatty acids have only C-C (no double bonds between the carbon atoms) so form linear hydrocarbon chains.
Unsaturated fatty acids have one or more C=C which causes the hydrocarbon chain to bend.

Question 3

What 3 components are needed to synthesise a triglyceride?

Answer 3

One glycerol bonds with 3 fatty acids in a condensation reaction releasing 3 water molecules.
Ester bonds form between hydroxyl groups (-OH) and carboxylic groups on fatty acids (-COOH)

Question 4

Physical properties of saturated and unsaturated triglycerides

Answer 4

Saturated:
Fatty acid chains only have C-C bonds and are straight.
Triglycerides pack closely together and stick more strongly.
Higher melting point.
Solid at room temperature.

Unsaturated:
Fatty acid chains have C=C bonds and are non-linear/ bent.
Triglycerides don’t pack closely together and stick less strongly.
Lower melting point.
Liquid at room temperature.

Question 5

Food test for lipids

Answer 5

If the sample is solid then grind it.
Add 2cm3 of ethanol and shake.
Add 2cm3 of cold water and shake.
Colour change from transparent to white/ milky emulsion.

Question 6

Similarities and differences between triglyceride and phospholipid

Answer 6

Triglyceride:
One glycerol bonded to 3 fatty acids.
Hydrophobic (non-polar molecule)

Phospholipid:
One glycerol bonded to 2 fatty acids with the 3rd replaced by a phosphate group.
Hydrophilic head and hydrophobic tail.

Question 7

Describe the formation of a phospholipid bilayer

Answer 7

Hydrophilic phosphate heads face outwards, attracted to water.
Hydrophobic fatty acid tails turn inwards, repelled by water.

Question 8

Explain the roles of phospholipid bilayers

Answer 8

Cell surface membrane:
Boundary between cells cytoplasm and external environment.
Different conditions inside the cell.
Partially controls the movement of substances in and out of the cell.
Non-polar/ lipid soluble molecules can diffuse directly through the bilayer.
Hydrophilic/ polar/ charged molecules require protein transport channels.

Organelle membranes:
Control entry/exit of substances.
Separate organelle contents from cytoplasm to allow specific metabolic reactions e.g. mitochondrial matrix and Krebs cycle.
Isolate enzymes e.g. lysosomes and hydrolytic enzymes.
Provide a surface for biochemistry e.g. thylakoids and the LDR

Question 9

Micelles

Answer 9

They include bile salts and fatty acids.
They make fatty acids more soluble in water.
Bring/ release fatty acids to cell/ lining of the ileum.
Maintain higher concentration of fatty acids to cell/ lining of the ileum.
Fatty acids absorbed by diffusion.