Biology paper 2

• Homeostasis


  The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• Enzymes and cells require very stable conditions in order to work
• The body has systems in place to keep the internal conditions optimum for the cells to function
• Internal conditions maintained by homeostasis

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Automatic control system


  Involves the nervous system or hormones
• Automatic control system


  1. Receptor cells detect changes in the environment

  2. Receptor cells pass information to a Coordination Center

  3. Coordination Center receives and processes the information

  4. Coordination Center sends instructions to the effector

  5. Effector carries out the response
• Stimulus


  A change to the environment
• Receptor cells


  Detect changes in the environment
• Coordination Center


  Receives and processes information from receptor cells
• Effector


  A muscle or gland that carries out the response
• The optimum level is stored
• Nervous system


  Consists of two parts: central nervous system (brain and spinal cord) and other nerves running to and from the central nervous system
• Homeostasis


  1. Stimulus

  2. Receptor

  3. Coordination Center

  4. Effector

  5. Response
• Neuron


  Another way of saying nerve cell
• Reflex arc


  1. Stimulus detected by receptor

  2. Electrical impulse passed along sensory neuron to central nervous system

  3. Electrical impulse passed along relay neuron in central nervous system

  4. Electrical impulse passed along motor neuron to effector

  5. Effector (muscle) contracts, response occurs
• Reflexes are automatic and rapid, with no decision-making by the conscious part of the brain
• Reflexes help to protect us from danger
• Measuring a person's reaction time

  1. Person 1 sits on a stool with good upright posture

  2. Person 1 places the forearm of their dominant arm across the table with hand overhanging the edge

  3. Person 2 holds a ruler vertically with the 0 cm mark between Person 1's thumb and first finger

  4. Person 2 tells Person 1 to prepare to catch the ruler

  5. Person 2 drops the ruler at a random time

  6. Person 1 catches the ruler with thumb and first finger as quickly as possible

  7. Person 2 records the measurement on the ruler level with Person 1's thumb

  8. Repeat the test several times and calculate the mean
• Reaction time


  Time taken for a person to respond to a stimulus
• The two people then switch places with Person 1 testing the reaction time of Person 2
• Independent variable


  The variable that is changed in an experiment
• Dependent variable


  The variable that is measured for each change in the independent variable
• Control variables


  • Variables that are kept constant to avoid affecting the dependent variable
  • Examples: distance between thumb and first finger, measuring at top of thumb, room conditions
• Other independent variables that could be investigated: effect of practice, dominant vs non-dominant hand, effect of chemicals like caffeine
• Need to check for any medical issues that could be affected by chemicals given to test subjects
• Experiments should be carried out in a lab where hazardous chemicals are not normally used
• Measuring a person's reaction time

  1. Person 1 sits on a stool with good upright posture

  2. Person 1 places the forearm of their dominant arm across the table with hand overhanging the edge

  3. Person 2 holds a ruler vertically with the 0 cm mark between Person 1's thumb and first finger

  4. Person 2 tells Person 1 to prepare to catch the ruler

  5. Person 2 drops the ruler at a random time

  6. Person 1 catches the ruler with thumb and first finger as quickly as possible

  7. Person 2 records the measurement on the ruler level with Person 1's thumb

  8. Repeat the test several times and calculate the mean
• Reaction time


  Time taken for a person to respond to a stimulus
• The two people then switch places with Person 1 testing the reaction time of Person 2
• Independent variable


  The variable that is changed in an experiment
• Dependent variable


  The variable that is measured for each change in the independent variable
• Control variables


  • Variables that are kept constant to avoid affecting the dependent variable
  • Examples: distance between thumb and first finger, measuring at top of thumb, room conditions
• Other independent variables that could be investigated: effect of practice, dominant vs non-dominant hand, effect of chemicals like caffeine
• Need to check for any medical issues that could be affected by chemicals given to test subjects
• Experiments should be carried out in a lab where hazardous chemicals are not normally used
• Measuring a person's reaction time

  1. Person 1 sits on a stool with good upright posture

  2. Person 1 places the forearm of their dominant arm across the table with hand overhanging the edge

  3. Person 2 holds a ruler vertically with the 0 cm mark between Person 1's thumb and first finger

  4. Person 2 tells Person 1 to prepare to catch the ruler

  5. Person 2 drops the ruler at a random time

  6. Person 1 catches the ruler with thumb and first finger as quickly as possible

  7. Person 2 records the measurement on the ruler level with Person 1's thumb

  8. Repeat the test several times and calculate the mean
• Reaction time


  Time taken for a person to respond to a stimulus
• The two people then switch places with Person 1 testing the reaction time of Person 2
• Independent variable


  The variable that is changed in an experiment
• Dependent variable


  The variable that is measured for each change in the independent variable