bio- nov 2021 past paper correction

• how an impulse passes from the relay neurone to the motor neurone.

  • impulse triggers release of chemical
  • known as transmitter
  • which is diffused and
  • released across the synapse
  • new impulse triggered in motor neurone
• explain function of reflex arc

  • is involuntary and
  • bypasses the brain
  • to allow a quick reaction
  • to protect body from harm
• describe how a scientist could compare the reaction times to changing coloured subjects

  • repeat measurements
  • calculate mean/average
  • control variables such as tiredness
• Name the organisation which defines health as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity

  National Health Organization
• State two ways that communicable diseases are different from non-communicable diseases.

  • communicable is passed from person to person
  • communicable caused by pathogens
• explain one way that spread of communicable disease can be prevented

  • vaccination/immunisation
  • to provide immunity and reduces chance of getting infected
• why are people with aids likely to be affected by TB

  • HIV destroys lymphocytes/weakens immune system
  • pathogen unable to prevent pathogen from entering the body
• 2 processes that occur in cells during prophase

  • chromosomes join
  • nuclear membrane breaks down
• define cytokinesis

  term used to describe the process which occurs after mitosis, when the cell divides into two.
• describe how to adjust microscope to view slide at desired magnification

  • choose magnification using objective lens
  • for higher magnification on eyepiece lens
  • use focussing wheel
• benefits of stem cell therapy

  • stem cells can differentiate
  • replace damaged cells
• risks of stem cell therapy

  • risk of rejection
  • uncontrolled cell division
• describe how cancer develops in the body

  • DNA mutation
  • uncontrolled cell division
  • lead to formation of tumour
• 2 safety precautions needed when removing blood

  • wear gloves
  • clean area of skin
  • cover wound after
  • use sterile needle
• how to improve enzyme experiment so that optimum is found

  • use smaller intervals
  • repeat the test and calculate the mean/average
• how to genetically modify bacterial cell to produce desired enzyme

  • cut plasmid with restriction enzyme
  • complimentary sticky ends
  • DNA ligase used to connect gene to plasmid
  • plasmid inserted back into bacterial cell
• how structure a and b enable fertilisation

  1. A is mitochondria- releases energy for respiration
  2. B is acrosome contains enzymes to get through egg cell membrane