1.3(lipids) + 1.7(water) + 1.8(inorganic Ions)

Question 1

Describe how to test for lipids in a sample

Answer 1

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

Question 2

Contrast saturated and unsaturated fatty acids

Answer 2

Saturated:
Contains 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 3

Relate the structure of triglycerides to their functions

Answer 3

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

Question 4

Describe the structure and function of phospholipids

Answer 4

Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head

Forms phospholipid bilayer in water = component of membranes

Tails can splay outwards = waterproofing

Question 5

Compare phospholipids and triglycerides

Answer 5

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

Question 6

Contrast phospholipids and triglycerides

Answer 6

Phospholipids:
2 fatty acids and 1 phosphate group attached
Hydrophilic head and 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 7

Are phospholipids and triglycerides polymers?

Answer 7

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

Question 8

Why is water a polar molecule?

Answer 8

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

O is more electronegative
H is more positive

Question 9

State 4 biologically important properties of water

Answer 9

Due to polarity and intermolecular H-bonds:

Metabolite/solvent for chemical reactions in the body
High specific heat capacity
High latent heat of vaporisation
Cohesion between molecules

Question 10

Explain why water is significant to living organisms

Answer 10

Solvent for polar molecules during metabolic reactions

Enables organisms to avoid fluctuations in core temperature

Cohesion-tension of water molecules in transpiration stream

Question 11

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

Answer 11

Ions that do not contain carbon atoms

Found in the cytoplasm and extracellular fluid

May be in high or very low concentrations

Question 12

Explain the role of hydrogen ions in the body

Answer 12

High concentration of H+ = low (acidic) pH

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

Question 13

Explain the role of iron ions in the body

Answer 13

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 14

Explain the role of sodium ions in the body

Answer 14

Involved in Co-transport for absorption of glucose and amino acids in lumen of gut

Involved in propagation of action potentials in neurons

Question 15

Explain the role of phosphate ions in the body

Answer 15

Component of:

DNA
ATP
NADP
cAMP

Question 16

How do triglycerides form?

Answer 16

Condensation reaction between 1 molecule of glycerol and 3 fatty acids form ester bonds