Lipids, Water, 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 which forms ester bonds

Question 3

Contrast saturated and unsaturated fatty
acids

Answer 3

Unsaturated:
● Contain C=C double bonds
● Lower melting point = liquid at room temperature
● Found in plant oils

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

Question 4

Relate the structure of triglycerides to their functions.

Answer 4

● 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
● Less dense than water = buoyancy of aquatic animals.

Question 5

Describe the structure and function of phospholipids.

Answer 5

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 6

Compare phospholipids and triglycerides.

Answer 6

● 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 7

Contrast phospholipids and triglycerides.

Answer 7

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 8

Are phospholipids and triglycerides polymers?

Answer 8

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

Question 9

Why is water a polar molecule?

Answer 9

O is more electronegative than H, so
attracts the electron density in the
covalent bond more strongly.

Question 10

State 4 biologically important properties of water.

Answer 10

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 11

Explain why water is significant to living organisms.

Answer 11

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

Question 12

What are inorganic ions and where are they found in the body?

Answer 12

● 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

Fe 2+ bonds to porphyrin ring to form haem
group in haemoglobin. Haem group has binding site to transport 1 molecule of O 2 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