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Biology_A-level_Cie

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  1. 1-1-the-microscope-in-cell-studies
    5 主题
  2. 1-2-cells-as-the-basic-units-of-living-organisms
    5 主题
  3. 2-1-testing-for-biological-molecules
    3 主题
  4. 2-2-carbohydrates-and-lipids
    8 主题
  5. 2-3-proteins
    6 主题
  6. 2-4-water
    2 主题
  7. 3-1-mode-of-action-of-enzymes
    5 主题
  8. 3-2-factors-that-affect-enzyme-action
    8 主题
  9. 4-1-fluid-mosaic-membranes
    4 主题
  10. 4-2-movement-into-and-out-of-cells
    12 主题
  11. 5-1-replication-and-division-of-nuclei-and-cells
    6 主题
  12. 5-2-chromosome-behaviour-in-mitosis
    2 主题
  13. 6-1-structure-of-nucleic-acids-and-replication-of-dna
    4 主题
  14. 6-2-protein-synthesis
    5 主题
  15. 7-1-structure-of-transport-tissues
    4 主题
  16. 7-2-transport-mechanisms
    7 主题
  17. 8-1-the-circulatory-system
    7 主题
  18. 8-2-transport-of-oxygen-and-carbon-dioxide
    5 主题
  19. 8-3-the-heart
    4 主题
  20. 9-1-the-gas-exchange-system
    6 主题
  21. 10-1-infectious-diseases
    3 主题
  22. 10-2-antibiotics
    3 主题
  23. 11-1-the-immune-system
    4 主题
  24. 11-2-antibodies-and-vaccination
    6 主题
  25. 12-1-energy
    5 主题
  26. 12-2-respiration
    11 主题
  27. 13-1-photosynthesis-as-an-energy-transfer-process
    8 主题
  28. 13-2-investigation-of-limiting-factors
    2 主题
  29. 14-1-homeostasis-in-mammals
    8 主题
  30. 14-2-homeostasis-in-plants
    3 主题
  31. 15-1-control-and-coordination-in-mammals
    12 主题
  32. 15-2-control-and-coordination-in-plants
    3 主题
  33. 16-1-passage-of-information-from-parents-to-offspring
    5 主题
  34. 16-2-the-roles-of-genes-in-determining-the-phenotype
    7 主题
  35. 16-3-gene-control
    3 主题
  36. 17-1-variation
    4 主题
  37. 17-2-natural-and-artificial-selection
    7 主题
  38. 17-3-evolution
    2 主题
  39. 18-1-classification
    5 主题
  40. 18-2-biodiversity
    7 主题
  41. 18-3-conservation
    6 主题
  42. 19-1-principles-of-genetic-technology
    11 主题
  43. 19-2-genetic-technology-applied-to-medicine
    4 主题
  44. 19-3-genetically-modified-organisms-in-agriculture
    2 主题
  45. 1-1-the-microscope-in-cell-studies
  46. 1-2-cells-as-the-basic-units-of-living-organisms
  47. 2-1-testing-for-biological-molecules
  48. 2-2-carbohydrates-and-lipids
  49. 2-3-proteins
  50. 2-4-water
  51. 3-1-mode-of-action-of-enzymes
  52. 3-2-factors-that-affect-enzyme-action
  53. 4-1-fluid-mosaic-membranes
  54. 4-2-movement-into-and-out-of-cells
  55. 5-1-replication-and-division-of-nuclei-and-cells
  56. 5-2-chromosome-behaviour-in-mitosis
  57. 6-1-structure-of-nucleic-acids-and-replication-of-dna
  58. 6-2-protein-synthesis
  59. 7-1-structure-of-transport-tissues
  60. 7-2-transport-mechanisms
  61. 8-1-the-circulatory-system
  62. 8-2-transport-of-oxygen-and-carbon-dioxide
  63. 8-3-the-heart
  64. 9-1-the-gas-exchange-system
  65. 10-1-infectious-diseases
  66. 10-2-antibiotics
  67. 11-1-the-immune-system
  68. 11-2-antibodies-and-vaccination
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The vital role of phospholipids

Structure

  • Phospholipids are a type of lipid, therefore they are formed from the monomer glycerol and fatty acids

  • Unlike triglycerides, there are only two fatty acids bonded to a glycerol molecule in a phospholipid as one has been replaced by a phosphate ion (PO43-)

  • As the phosphate is polar it is soluble in water and described as hydrophilic

  • The fatty acid ‘tails’ are non-polar and therefore insoluble in water and described as hydrophobic

Diagram of a phospholipid showing a hydrophilic polar head with phosphate and glycerol, and two hydrophobic nonpolar fatty acid tails.
Phospholipids are the major components of cell surface membranes. They have fatty acid tails that are hydrophobic and a phosphate head, that is hydrophilic, attached to a glycerol molecule.

  • Phospholipids are amphipathic (they have both hydrophobic and hydrophilic parts)

  • As a result of having hydrophobic and hydrophilic parts phospholipid molecules form monolayers or bilayers in water

Diagram of a phospholipid bilayer showing hydrophilic phosphate heads (polar) and hydrophobic fatty acid tails (non-polar) with extracellular and intracellular labels.
In the presence of water due to the hydrophobic and hydrophilic parts phospholipids will form monolayers or bilayers.

Role of phospholipids

  • They are the main component (building block) of cell membranes

  • Due to the presence of hydrophobic fatty acid tails, a hydrophobic core is created when a phospholipid bilayer forms

    • This acts as a barrier to water-soluble molecules

  • The hydrophilic phosphate heads form hydrogen bonds with water allowing the cell membrane to be used to compartmentalise

    • This enables the cells to organise specific roles into organelles helping with efficiency

  • Composition of phospholipids contributes to the fluidity of the cell membrane

    • If there are mainly saturated fatty acid tails then the membrane will be less fluid

    • If there are mainly unsaturated fatty acid tails then the membrane will be more fluid

  • Phospholipids control membrane protein orientation

    • Weak hydrophobic interactions between the phospholipids and membrane proteins hold the proteins within the membrane but still allow movement within the layer

Feature 

Phospholipid

Triglyceride

Number of fatty acid tails

2

3

Presence of phosphate

Yes

No

Number of ester bonds

2

3

Polar or non-polar

Polar phosphate head

Non-polar

Number of water molecules released during formation

3

3

Function

Cell membrane component 

Energy storage

Examiner Tips and Tricks

Ensure you know the difference between phospholipids and triglycerides!