Lipids, water and inorganic ions

Question 1

Describe how to test for lipids in a sample.

Answer 1

1. Dissolve solid samples in ethanol.
2. Add an equal volume of water and shake.
3. Positive result: milky white emulsion forms

Question 2

How do triglycerides form?

Answer 2

condensation reaction between 1 molecule of glycerol & 3 fatty acids forms ester bonds

Question 3

Describe saturated fatty acids

Answer 3

● Contain only single bonds
● Straight-chain molecules have many contact points
● Higher melting point = solid at room temperature
● Found in animal fats

Question 4

Describe unsaturated fatty acids

Answer 4

● Contain C=C double bonds
● ‘Kinked’ molecules have fewer contact points
● Lower melting point = liquid at room temperature
● Found in plant oils

Question 5

Relate the structure of triglycerides to their functions.

Answer 5

● High energy: mass ratio = high calorific value from oxidation (energy storage).
● Insoluble hydrocarbon chain = no effect on water potential of cells & used for waterproofing.
● Slow conductor of heat = thermal insulation e.g. adipose tissue.
● Less dense than water = buoyancy of aquatic animals

Question 6

Describe the structure and function of phospholipids.

Answer 6

Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails & 1 hydrophilic polar phosphate head.
● Forms phospholipid bilayer in water = component of membranes.
● Tails can splay outwards = waterproofing.

Question 7

Compare phospholipids and triglycerides.

Answer 7

● Both have glycerol backbone.
● Both may be attached to a mixture of saturated, monounsaturated &
polyunsaturated fatty acids.
● Both contain the elements C, H, O.
● Both formed by condensation reactions.

Question 8

Contrast phospholipids and triglycerides.

Answer 8

phospholipids:
● 2 fatty acids & 1 phosphate group attached
● Hydrophilic head & hydrophobic tail
● Used primarily in membrane formation
triglycerides:
● 3 fatty acids attached
● Entire molecule is hydrophobic
● Used primarily as a storage molecule (oxidation releases energy)

Question 9

Are phospholipids and triglycerides polymers?

Answer 9

No; they are not made from a small repeating unit. They are macromolecules.

Question 10

Why is water a polar molecule?

Answer 10

O is more electronegative than H, so attracts the electron density in the
covalent bond more strongly.
Forms O 𝛿- (slight negative charge) & H 𝛿+ (slight positive charge)

Question 11

State 4 biologically important properties of water.

Answer 11

due to polarity & intermolecular H-bonds:
● Metabolite / solvent for chemical reactions in the body.
● high specific heat capacity.
● high latent heat of vapourisation.
● cohesion between molecules.

Question 12

Explain why water is significant to living organisms.

Answer 12

● Solvent for polar molecules during metabolic reactions.
● Enables organisms to avoid fluctuations in core temperature.
● Cohesion-tension of water molecules in transpiration stream.

Question 13

What are inorganic ions and where are they found in

the body?

Answer 13

● Ions that do not contain carbon atoms.
● Found in cytoplasm extracellular fluid.
● May be in high or very low concentrations.

Question 14

Explain the role of hydrogen ions in the body.

Answer 14

● High concentration of H+ = low (acidic) pH.

● H+ ions interact with H-bonds & ionic bonds in tertiary structure of proteins, which can cause them to denature.

Question 15

Explain the role of iron ions in the body.

Answer 15

Fe2+ bonds to porphyrin ring to form haem group in haemoglobin.
Haem group has binding site to transport 1 molecule of O2
around body in bloodstream.
4 haem groups per haemoglobin molecule.

Question 16

Explain the role of sodium ions in the body.

Answer 16

Involved in co-transport for absorption of glucose & amino acids in lumen of gut
Involved in propagation of action potentials in neurons

Question 17

Explain the role of phosphate ions in the body.

Answer 17

component of:
● DNA
● ATP
● NADP
● cAMP