Biology

• Pathogens are microorganisms that cause infectious disease
• Communicable diseases are infectious so they can be spread between animals and plants
• Types of pathogens


  • Bacteria
  • Viruses
  • Fungi
  • Protists
• Bacterial pathogens


  May reproduce quickly in the body and produce toxins that damage tissue
• Viral pathogens


  Infect and reproduce themselves inside body cells
• Non-specific human defense systems


  • Hair and mucus in nose
  • Stomach acid
  • Skin as physical barrier
• White blood cell defense against pathogens


  1. Phagocytosis

  2. Antibody production

  3. Antitoxin production
• Vaccination


  Injection of dead or weakened pathogens to stimulate antibody production and memory cells
• Pathogens and diseases


  • Salmonella (food poisoning)
  • Gonorrhea (sexually transmitted)
  • Measles (viral)
  • HIV (viral)
  • Tobacco mosaic virus (plant)
  • Rose black spot (fungal)
  • Malaria (protist)
• Antibiotics


  Kill bacterial pathogens, do not work on viruses
• Painkillers and other medicines


  Treat symptoms, do not kill pathogens
• Drug development and testing


  1. Possible drugs selected

  2. Pre-clinical trials on cells/tissues/animals

  3. Clinical trials on volunteers

  4. Peer review
• Monoclonal antibodies


  Produced from a single clone of cells, specific to one protein antigen
• Uses of monoclonal antibodies


  • Diagnosis (e.g. pregnancy tests)
  • Laboratory detection of pathogens or chemicals
  • Research to locate molecules
  • Treatment of disease (e.g. cancer)
• Causes of plant diseases


  • Spots on leaves
  • Discoloration of leaves
  • Malformed stems/leaves
  • Stunted growth
  • Decay or rot
  • Pest infestations
• Plant nutrient deficiencies


  • Iron deficiency
  • Nitrate deficiency
  • Magnesium deficiency
• Plant physical defense responses


  • Layers of dead cells (e.g. bark)
  • Waxy cuticles on leaves
  • Cellular cell walls
• Plant chemical defense responses


  • Antibacterial chemicals
  • Poisons in plant tissue
• Plant mechanical adaptations


  • Thorns
  • Hairs
  • Leaves that droop or curl
  • Mimicry
• Cells

  Can be seen with a normal light microscope, but subcellular structures are not visible. Electron microscopes have better resolving power and resolution to see finer details.
• Cell size

  Can be calculated by knowing the magnification of the microscope: Magnification = Image size / Object size
• Cell types

  • Eukaryotic cells (have a nucleus)
  • Prokaryotic cells (no nucleus, DNA in a ring called a plasmid)
• Eukaryotic and prokaryotic cells

  • Contain similar organelles or subcellular structures
• Cell membrane

  • Keeps everything inside the cell, semi-permeable to allow certain substances to pass through
• Plant cells and most bacteria

  • Have an extra cell wall made of cellulose, providing a rigid structure
• Cytoplasm

  The liquid that makes up the cell, where most chemical reactions take place
• Mitochondria

  • Where respiration takes place, releasing energy for the cell to function
• Ribosomes

  • Where proteins are assembled or synthesized
• Plant cells

  • Contain chloroplasts with chlorophyll, where photosynthesis takes place
  • Contain a permanent vacuole to store sap
• Bacterial multiplication

  1. Binary fission, number doubles every 10 minutes

  2. Can be demonstrated through a practical using agar in a Petri dish and aseptic technique
• Diploid cells

  Cells with 23 pairs of chromosomes (e.g. human cells)
• Haploid cells

  Cells with 23 single chromosomes (e.g. gametes)
• Cell division

  Mitosis: Genetic material is duplicated, number of ribosomes and mitochondria is doubled, nucleus breaks down, chromosomes are pulled to opposite sides, new nuclei form in the two identical cells
• Cell specialization

  • Cells specialize to fulfill different functions (e.g. nerve, muscle, root hair, xylem, phloem, stem cells)
• Stem cells

  Unspecialized cells that can differentiate into various cell types, found in embryos and bone marrow
• Diffusion

  The movement of molecules or particles from an area of high concentration to an area of low concentration, down the concentration gradient, without requiring energy input
• Osmosis

  The diffusion of water across a semi-permeable membrane, from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration)
• Factors affecting diffusion and osmosis rates

  Increased concentration difference, temperature, or surface area
• Practical on osmosis

  Cut equal-size vegetable cylinders, weigh, place in varying sugar solutions, reweigh after a day, calculate percentage change in mass, plot against sugar concentration to find the concentration with no change (same as inside the cells)
• Active transport

  The movement of substances through a membrane against a concentration gradient, using energy