Flashcards - Topic 1.3 Lipids 1.7 Water 1.8 Inorganic ions - AQA Biology A-level
(16 cards)
Describe how to test for lipids in a sample.
- Dissolve solid samples in ethanol.
- Add an equal volume of water and shake.
- Positive result: milky white emulsion forms
How do triglycerides form?
Condensation reaction between 1 molecule of glycerol & 3 fatty acids forms ester bonds.
Image source: OpenStax College, CC BY 3.0
Contrast saturated and unsaturated fatty acids.
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
Relate the structure of triglycerides to their functions.
? 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.
Describe the structure and function of phospholipids.
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.
Compare phospholipids and triglycerides.
? 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.
Contrast phospholipids and triglycerides.
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)
Are phospholipids and triglycerides polymers?
No; they are not made from a small repeating unit. They are macromolecules.
Why is water a polar molecule?
O is more electronegative than H, so attracts the electron density in the covalent bond more strongly. Forms O ??- (slight negative charge) & H ??+ (slight positive charge).
State 4 biologically important properties of water.
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.
Explain why water is significant to living organisms.
? Solvent for polar molecules during metabolic reactions.
? Enables organisms to avoid fluctuations in core temperature.
? Cohesion-tension of water molecules in transpiration stream.
What are inorganic ions and where are they found in the body?
? Ions that do not contain carbon atoms.
? Found in cytoplasm & extracellular fluid.
? May be in high or very low concentrations.
Explain the role of hydrogen ions in the body.
? 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.
Explain the role of iron ions in the body.
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.
Explain the role of sodium ions in the body.
Involved in co-transport for absorption of glucose & amino acids in lumen of gut (Topic 2.3). Involved in propagation of action potentials in neurons (Topic 6.2).
Explain the role of phosphate ions in the body.
Component of:
- DNA
- ATP
- NADP (Topic 5.1)
- cAMP (Topic 6.4)
