response to change

• What is a stimulus in biology?

  Something that can be detected by an organism
• What is the role of a receptor?

  To detect changes causing a stimulus
• What is a response in biological terms?

  Movement or change in behavior due to stimulus
• What is a taxis?

  • A response involving movement in a specific direction
  • Positive taxis: movement towards stimulus
  • Negative taxis: movement away from stimulus
• What is kinesis?

  • A response involving random movement
  • Speed and frequency of direction change increase
  • Aimed at entering different conditions rapidly
• How does a woodlouse respond in a dry area?

  It speeds up and changes direction frequently
• What are tropisms in plants?

  • Growth responses controlled by directional stimuli
  • Example: Phototropism - growth towards light
  • Shoots are positively phototropic; roots negatively phototropic
• What hormone controls plant growth?

  Indoleacetic acid (IAA)
• How does uneven distribution of IAA affect plant growth?

  It causes uneven growth of the plant
• What happens when a shoot is illuminated from one side?

  Auxins move to the shaded side, causing bending
• What is gravitropism in roots?

  • IAA builds up on the lower side of the root
  • IAA inhibits growth in roots
  • Causes the root to bend downwards
• What is a reflex arc?

  • Rapid automatic responses to harmful stimuli
  • Pathway: Stimulus → Receptor → Sensory Neurone → Intermediate Neurone → Motor Neurone → Effector → Response
• What does the sensory neurone do in a reflex arc?

  Carries nerve impulse to the spinal cord
• Where is the intermediate neurone located?

  Entirely in the spinal cord
• What is the function of the motor neurone?

  Carries impulse to the effector
• What types of receptors are there?

  • Photoreceptors: detect light changes
  • Mechanoreceptors: detect pressure and vibrations
• Where are Pacinian Corpuscles located?

  Deep in the skin, fingers, and feet
• What happens to sodium channels in Pacinian Corpuscles under pressure?

  They open, allowing sodium ions to enter
• What is the result of sodium influx in Pacinian Corpuscles?

  It causes depolarization and generator potential
• What are photoreceptors in the eye?

  • Light receptors located in the retina
  • Control light entry via the iris
  • Two types: cones (color vision) and rods (monochromatic vision)
• What pigment do cone cells contain?

  Iodopsin
• Why do cone cells require bright light?

  They are not sensitive to low light
• How do rod cells differ from cone cells?

  Rod cells are sensitive to low light
• What is myogenic contraction in the heart?

  • Heart initiates its own contraction
  • Sinoatrial node acts as the pacemaker
• What is the role of the sinoatrial node?

  It initiates electrical stimulation for heart contraction
• How does the heart's contraction sequence work?

  Atria contract before ventricles due to conduction delay
• What factors increase heart rate?

  • High carbon dioxide concentration
  • Changes in blood pressure
• How do chemoreceptors affect heart rate?

  They detect pH changes and send impulses to increase heart rate
• What do baroreceptors monitor?

  Changes in blood pressure
• What is the structure of neurones?

  • Cell body with nucleus and organelles
  • Dendrites conduct impulses towards cell body
  • Axons conduct impulses away from cell body
• What is resting potential in neurones?

  Voltage of -70mV due to ion imbalance
• How is resting potential maintained?

  By the sodium-potassium pump and ion channels
• What happens during depolarization?

  Sodium channels open, allowing sodium influx
• What is hyperpolarization?

  When potential difference becomes more negative than resting potential
• What is saltatory conduction?

  • Action potential jumps between nodes of Ranvier
  • Speeds up nerve impulse transmission
• What factors affect the speed of nerve impulses?

  1. Presence of myelin sheath
  2. Diameter of the axon
  3. Temperature
• What is the refractory period?

  Time when neurone membrane cannot be excited
• What does the all-or-nothing principle state?

  Action potentials are produced only if threshold is reached
• What are the roles of synapses?

  • Prevent action potentials from going in wrong direction
  • Amplify effects of low frequency action potentials
  • Some synapses can be inhibitory
• How do synapses amplify low frequency action potentials?

  Through temporal or spatial summation