Lipids + Water + Inorganic ions

Question 2

Describe how to test for lipids in a sample

Answer 2

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

Question 3

How do triglycerides form?

Answer 3

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

Question 4

Contrast saturated & unsaturated fatty acids

Answer 4

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

Unsaturated:
- 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 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 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 & triglycerides

Answer 7

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

Question 8

Contrast phospholipids & 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

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

forms O S- (slight negative) & H S- (slight positive charge)

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 & 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 13

Explain role of hydrogen ions in the body

Answer 13

• 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 14

Explain role of iron ions in the body

Answer 14

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 15

Explain role of sodium ions in the body

Answer 15

Involved in co-transport for absorption of glucose & amino acids in lumen of gut

Involved in propagation of action potentials in neurons

Question 16

Explain role of phosphate ions in the body

Answer 16

component of:
- DNA
- ATP
- NADP
- cAMP