Unit 4

• Plant cells


  Eukaryotic cells found in plants and algae
• Organelles in plant cells

  • Cell wall
  • Chloroplast
  • Amyloplast
  • Vacuole
  • Tonoplast
  • Plasmodesmata
  • Pits
  • Middle lamella
• Cell wall


  • Surrounds the cell outside of the cell surface membrane
  • Made of cellulose
  • Strengthens and supports the cell
  • Prevents the cell changing shape
  • Contains pores to allow movement of substances
• Chloroplast


  • Small, flattened structure
  • Contains a double membrane
  • Inner membrane is stacked into thylakoid
  • Contains chlorophyll which absorbs light for photosynthesis
• Amyloplast


  • Synthesises and stores starch molecules
  • Breaks down starch to glucose when the cell requires it
• Vacuole


  • Membranous sac that contains sap (dissolved sugars and salts)
  • Allows the cell to become turgid
  • Isolates unwanted chemicals from the rest of the cell
• Tonoplast


  Membrane surrounding a vacuole
• Plasmodesmata


  Channels of cytoplasm that pass between adjacent cell walls, allowing fast communication and exchange of substances between cells
• Pits


  Sections of the cell wall which adjacent plant cells can exchange fluid or communicate through
• Middle lamella


  A layer made of pectin that lies between adjacent plant cells, sticking the cell walls together
• Starch


  • Stores energy in plants
  • Mixture of two polysaccharides: amylose and amylopectin
• Amylose


  • Unbranched chain of glucose molecules joined by 1,4 glycosidic bonds
  • Coiled and compact, can store a lot of energy
• Amylopectin


  • Branched and made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds
  • Rapidly digested by enzymes, energy is released quickly
• Starch granules are laid down in successive rings
• Cellulose


  • Component of cell walls in plants
  • Composed of long, unbranched chains of beta glucose joined by glycosidic bonds
• Microfibrils


  • Made of long cellulose chains linked together by hydrogen bonds
  • Form long threads that provide structural support in plant cells
• Secondary cell wall


  • Second cell wall formed between the original cell wall and the cell surface membrane
  • Begins to grow once the cell has stopped growing
  • Made of parallel layers of microfibrils of cellulose with other polysaccharide additions
• Lignin


  • Polysaccharide added to the secondary cell wall of plant cells in xylem vessels and sclerenchyma fibres
  • Makes the cell walls less flexible and more rigid, adding strength to the vascular bundle
• Xylem vessels


  Transport water and inorganic ions around the plant
• Sclerenchyma fibres


  Support the plant
• Xylem vessels and sclerenchyma fibres are made from dead cells
• Phloem


  • Transports organic solutes via translocation
  • Made of living cells lined end to end forming a sieve tube element, with surrounding companion cells
• Xylem are found towards the centre of the plant, followed by the phloem vessels, followed by sclerenchyma the furthest out from the centre
• Renewable and sustainable


  Plant material can be maintained at a constant level, unlike non-renewable resources like crude oil
• Plant-based substitutes for crude oil and fossil fuels

  • Biodiesel made from ethanol synthesised from the fermentation of plants
• Plant fibres


  • Very strong, can be used to make materials like ropes and fabrics
  • Production is cheaper than oil-based ones
  • Starch can be used to make bioplastics and bioethanol
  • Substances derived from plants have antimicrobial and therapeutic properties
• Xylem vessel


  Responsible for transporting ions and water from the roots to other areas of the plant
• Water is required to keep cells turgid
• Lack of water causes plants to wilt, reducing their photosynthesis
• Ions required for plant growth and development

  • Nitrate ions
  • Calcium ions
  • Phosphate ions
  • Magnesium ions
• Bacterial growth


  • Exponential growth in optimal conditions
  • Optimal conditions: warmth, moisture, nutrients, optimum pH, oxygen
• Drug testing has become more vigorous over time, particularly after the thalidomide case
• William Withering's digitalis soup


  • Through trial and error, Withering developed a remedy for dropsy using foxglove and its active ingredient digitalis
  • Too much digitalis poisoned patients, too little had no effect, Withering found the optimum dosage
• Stages of drug testing

  • Testing on human tissues and cells, computer models
  • Testing on animals
  • Clinical trials: Phase 1 (testing on healthy volunteers), Phase 2 (testing on small group with illness), Phase 3 (testing on large group)
• Drug testing requirements


  • Placebo group
  • Double-blind trials
  • Peer review
• Placebo effect


  The patient's condition improves because psychologically they believe the drug will make them better, so they do make some improvement
• Drug testing


  • Need to compare to the placebo group of patients to observe whether the drug is more effective than the psychological effects
• Blind trial


  Where the patient does not know whether they have the active drug or the placebo drug; this is so the placebo effect can be observed
• Double-blind trial


  Where neither the patient nor the doctor knows which drug they have; this is to stop any subconscious bias the doctor may have when assessing the patient and their improvement
• Peer review


  Studies such as drug testing are reviewed by other professionals to be sure they're accurate, well carried out and significant