learn these

• Sensory neurones:

  carry impulses to the CNS from receptors

  • Dendrites (near receptors): collect impulses from receptor cells
  • Dendron: carries impulses from dendrite to cell body
  • Axon: carries impulses away from cell body
  • Axon endings: pass impulses to other neurones
  • Myelin sheath: insulates the neurone, speeding up the transmission
• Motor neurones:

  carry impulses from the CNS to the effectors

  Dendrites: receive impulses from other neurones

  Axon: carries electrical impulse over long distances through the body

  Myelin sheath: insulates the neurone, speeding up transmission by making the impulse jump from one gap to the next

  Nerve ending: transmits the impulse to an effector, such as a muscle or a gland
• Genetic engineering:

  1. restriction enzymes cut DNA leaving sections with unpaired bases at the ends, called sticky ends
  2. Same restriction enzymes used to cut plasmids of bacteria open, leaving complementary sticky ends
  3. Sticky ends of both the human DNA and the bacterial DNA are joined together using ligase
  4. Plasmids are inserted back into bacteria to be grown in huge fermenters where they make human insulin
• DNA is a polymer made up of:

  • two strands coiled to form a double helix
  • strands linked by a series of complementary base pairs (G-C, A-T) joined together by weak hydrogen bonds
  • nucleotides that consist of a sugar and phosphate group with one of the four different bases attached to the sugar
• Common diseases:

  • cholera (bacteria) causes diarrhoea - water
  • tuberculosis (bacteria) causes lung damage - airborne
  • Chalara ash dieback (fungi) causes leaf loss and bark lesions - airborne
  • malaria (protists) causes damage to blood and liver - animal vectors
  • HIV (virus) destroys white blood cells, leading to the onset of AIDS - STD
• Physical barriers:

  • unbroken skin is too thick for pathogen to get through
  • mucus in nose traps pathogen
  • Cilia lining the lungs move pathogens and mucus to back of throat where they are swallowed

  Chemical barriers:

  • lysozyme (in tears, saliva and mucus) kill bacteria by digesting their cell walls
  • hydrochloric acid in stomach kills pathogens in food and drink
• The Immune System:

  1. each pathogen has unique antigens on its surface
  2. a lymphocyte with an antibody that fits the antigen is activated
  3. the lymphocyte divides many times to produce clones of identical lymphocytes
  4. some lymphocytes produce antibodies which stick to pathogen and destroy it
  5. other lymphocytes stay in the blood as memory lymphocytes which are ready to respond immediately if the same antigen returns
• bases in DNA:

  A= adenine

  T= thymine

  C= cytosine

  G=guanine

  A binds with T

  C binds with G
• Malaria:

  1. infected mosquito bites a human and injects the protist that causes malaria
  2. infects live and red blood cells
  3. Mosquito becomes infected with parasite when it bites the person
  4. Mosquito bits a second person, spreading malaria
• DNA extraction from fruit:

  1. Grind up fruit with pestle and mortar to break open cells
  2. Pour in detergent to break down cell membrane and membrane around the nucleus
  3. Add salt to make the DNA stick together
  4. Pour mixture through filter funnel into boiling tube
  5. Add protease enzyme
  6. Place boiling tube into beaker of water and leave for 10 minutes
  7. tilt boiling tube and gently pour ice cold ethanol down side of tube to precipitate the DNA