Part 2

• Describe the cellulose cell wall of plants(6 marks)

  • Cellulose is made up of β-glucose monomers (1)
  • Monomers joined together by 1,4 glycosidic bonds in a condensation reaction (1)
  • Alternate β-glucose monomers are inverted in the chain (1)
  • Cellulose molecules are long, straight chains (1)
  • Many cellulose molecules, held together by hydrogen bonds, form cellulose microfibrils (1)
  • In primary cell walls, the cellulose microfibrils are embedded in a matrix of hemicellulose and pectin (1)
• Describe the function of lignin in the secondary cell wall of xylem and sclerenchyma(3 marks)

  • Lignin holds the cellulose microfibrils together and keeps them parallel; layers arranged in a net (1)
  • Lignin provides structural support/ tensile strength (1)
  • Lignin makes the walls waterproof (1)
• Describe the structure and function of xylem vessels(4 marks)

  • Transport of water and mineral ions
  • Cells with no cytoplasm, no cell contents
  • Cells with no end walls to allow water and mineral ions to move vertically
  • Pits (no secondary cell wall) to allow water and mineral ions to move horizontally
  • Lignin provides tensile strength and makes the walls waterproof
• Structure and function of sclerenchyma fibres


  • Lignin provides tensile strength and makes the walls waterproof
• Structure and function of phloem vessels


  • Transport of organic solutes (amino acids and sucrose)
  • Consists of sieve tube elements and companion cells
  • Sieve tube elements (ST) connected end-to-end by sieve end plates, which allow solutes to move from one cell to the next; very little cytoplasm and few or no organelles
  • Accompanied by a companion cell (CC) containing a nucleus and mitochondria, supplying energy to the ST for actively loading solutes
• Role of magnesium ions in plants


  • Magnesium is essential in production of chlorophyll molecules
  • Chlorophyll is required to produce glucose during photosynthesis
  • Glucose needed for growth and to produce cellulose in cell walls
• Magnesium ions deficiency limits production of chlorophyll, resulting in less photosynthesis, and a lack of glucose. Therefore, plants may have yellow leaves/ stunted growth.
• Role of calcium ions in plants


  • Calcium ions are essential in production of calcium pectate in the middle lamella
  • Middle lamella is a glue between cells 'cement'
• Calcium ions deficiency limits production of calcium pectate in the middle lamellae; new leaves cannot grow fully.
• Role of nitrate ions in plants


  • Nitrate ions are essential in production of amino acids (for protein synthesis)
  • Proteins required for growth and repair
  • and nitrogenous bases in nucleotides (for nucleic acids synthesis)
• Why production of products made of plant fibres is sustainable


  • Plants are a renewable resource, more plants can be grown
  • Plants available to future generations
• Preclinical trials


  • testing on cell culture/ tissue culture/ animals – to determine toxicity
  • benefits to human must outweigh harm done to animals
• Phase 1 of clinical trials


  • testing on healthy volunteers
  • use different concentrations to determine safe dose
  • to determine side effects
  • to determine how drug is metabolised
• Phase 2 of clinical trials


  • testing on a small number of individuals with the medical condition
  • to see whether drug is effective in treating the medical condition
  • to determine less-common side effects
• Phase 3 of clinical trials


  • testing on a large number of individuals with the medical condition
  • to gather more data for statistical analysis
  • Placebo
  • Double-blind
• Placebo


  Placebo (inactive drug) – placebo is used as a control in comparison with the actual drug to ensure the active drug is causing the effect/ improvement is not due to a psychological effect
• Double-blind trial


  Neither patients nor doctors know whether the treatment contains the new drug or placebo – this removes bias from results
• How William Withering used digitalis soup to treat heart disease


  1. Used a foxglove extract (digitalis soup), not pure digitalis

  2. Used digitalis on individuals with the medical condition

  3. Used different concentrations to determine safe dose

  4. Did not use a placebo group
• Antimicrobial properties


  Ability to kill or inhibit the growth of microorganisms
• Antibacterial property


  Ability to kill or inhibit the growth of bacteria
• Aseptic techniques


  • Disinfect working surface before and after use
  • Only lift lids of agar plates partially and for a minimum time
  • Only dispose of used agar plates after they have been autoclaved
  • Working carefully near a Bunsen Burner to provide a convection current