Responding to Changes in Environment

• What is the definition of a stimulus?

  A detectable change in the environment
• How do organisms increase their chance of survival?

  By responding to stimuli via response mechanisms
• What are tropisms in plants?

  • Responses to stimuli via growth
  • Positive tropism: growth towards stimulus
  • Negative tropism: growth away from stimulus
• What are the two stimuli that plants respond to in tropisms?

  Light and gravity
• What is the role of indoleacetic acid (IAA) in plants?

  Controls cell elongation and inhibits root growth
• Where is IAA produced in plants?

  In the tip of the root and shoot
• How does IAA affect the shoots in phototropism?

  It diffuses to the shaded side, causing elongation
• What happens to the roots when exposed to high concentrations of IAA?

  Cell elongation is inhibited on the lower side
• What is negative phototropism in roots?

  Roots grow downwards towards gravity
• What is gravitropism in shoots?

  Growth response to gravity in the shoots
• How does IAA affect the shoots in gravitropism?

  It diffuses from upper to lower side, causing elongation
• What is positive gravitropism in roots?

  Roots bend downwards towards gravity
• What are taxis and kinesis in organisms?

  • Taxis: directional movement towards or away from stimuli
  • Positive taxis: towards favorable stimulus
  • Negative taxis: away from unfavorable stimulus
  • Kinesis: non-directional movement based on stimulus intensity
• What is the kinesis response when an organism encounters harmful stimuli?

  Increases rate of changing direction
• What happens if an organism is surrounded by negative stimuli?

  Rate of turning decreases to move straight
• Why do organisms prefer dark areas?

  To avoid predators and prevent drying out
• What are simple reflexes in complex organisms?

  Rapid automatic responses to stimuli
• What is the structure of the nervous system?

  • Peripheral Nervous System (PNS)
  • Receptors, sensory, and motor neurons
  • Central Nervous System (CNS)
  • Coordination center: brain and spinal cord
• What is a reflex arc?

  A pathway for reflex actions involving neurons
• How many neurons are in a reflex arc?

  Three neurons
• What is the role of the sensory neuron in a reflex arc?

  Detects stimulus and sends impulse to spinal cord
• What is the role of the relay neuron in a reflex arc?

  Located in the CNS, connects sensory and motor neurons
• What is the role of the motor neuron in a reflex arc?

  Carries impulse to an effector to carry out response
• Why are reflexes considered involuntary?

  They do not require conscious thought
• What is the purpose of a reflex action?

  Protects against damage and helps escape predators
• What is a generator potential?

  Establishment of a potential leading to a response
• What are the three types of receptors mentioned?

  Pacinian corpuscle, rod cells, cone cells
• What does the Pacinian corpuscle respond to?

  Pressure changes
• Where are Pacinian corpuscles primarily located?

  Deep in the skin, mainly fingertips and feet
• What type of channels do Pacinian corpuscles have?

  Stretch-mediated sodium ion channels
• How do rod cells process images?

  In black and white, low light intensities
• What is retinal convergence in rod cells?

  Multiple rod cells connect to one bipolar cell
• What is low visual acuity?

  Blurry vision due to retinal convergence
• What do cone cells process?

  Images in color
• What is the function of iodopsin in cone cells?

  Absorbs different wavelengths of light
• How does the distribution of rods and cones vary in the retina?

  Uneven distribution, with more cones at the fovea
• What is myogenic contraction in cardiac muscle?

  Contraction without input from the nervous system
• What is the role of the sinoatrial node (SAN)?

  Natural pacemaker of the heart
• What does the atrioventricular node (AVN) do?

  Releases wave of depolarization after SAN
• What is the function of the bundle of His?

  Transmits electrical activity through cardiac muscle