Response and regulation

• Sense organs


  Contain receptor cells that detect external stimuli and send electrical signals along neurones to the central nervous system (CNS) to coordinate a response
• Sense organs


  • Eye
  • Ear
  • Nose
  • Tongue
  • Skin
• Stimuli detected by sense organs

  • Light
  • Sound
  • Chemical smells
  • Chemical tastes
  • Pain, pressure, temperature
• Reflex response


  1. Rapid

  2. Automatic

  3. Generally protective
• Reflex arc


  1. Stimulus

  2. Receptor

  3. Sensory neurone

  4. Relay neurone

  5. Coordinator

  6. Motor neurone

  7. Effector
• Reflex arc


  • Path taken by an electrical impulse from stimulus to response by an effector (muscle or gland)
  • Withdrawal action reflex is an example
• Eye


  • Iris - muscles that alter size of pupil to control amount of light entering
  • Sclera - protective, tough white outer coat
  • Choroid - pigmented layer which absorbs light to prevent reflection, also contains blood vessels
  • Retina - light sensitive layer, an image is formed here, impulses sent to optic nerve
  • Cornea - clear part of sclera allows light to enter and refracts light entering pupil
  • Pupil - hole in centre of iris which allows light to enter
  • Blind spot - where the optic nerve leaves the eye, there are no light sensitive cells
  • Optic nerve - carries impulses from retina to brain
  • Lens - changes shape to focus light onto retina
• Negative feedback


  Any change from the balance in optimal internal conditions results in the body's hormonal and nervous systems compensating for the change and restoring the balance
• Homeostasis


  Maintenance of a constant internal environment
• Regulating glucose


  1. Eating increases glucose in blood

  2. Exercising decreases glucose in the blood

  3. Pancreas detects increase and releases insulin into the blood

  4. Pancreas detects decrease and releases glucagon into the blood

  5. Insulin travels to liver and liver turns glucose into insoluble glycogen for storage

  6. Glucagon tells the liver to turn stored glycogen into glucose and release into the blood

  7. Glucose level decreases/increases to normal levels
• Diabetes


  • Condition where you are unable to control your own blood glucose levels
  • In Type I diabetes the body does not release insulin
  • In Type II diabetes the body cells do not respond to the chemical signal from insulin
• Regulating temperature - Too hot

  1. Hairs lie flat

  2. Sweating - A layer of liquid sweat made by sweat glands, carried up by sweat ducts and released by sweat pores onto the skin and evaporates removing heat energy

  3. Vasodilation - Blood vessels in the skin widen so more heat from the blood is lost to the environment
• Regulating temperature - Too cold

  1. Hairs stand on end to trap a layer of insulating air over skin reducing heat loss

  2. Shivering - Involuntary contraction of the muscles increases respiration and the release of heat energy

  3. Vasoconstriction - Blood vessels in the skin get narrower so less heat is lost from the blood to the environment
• Lifestyle factors


  • Diet - A diet high in sugars and carbohydrates can lead to obesity and type II diabetes
  • Drug and alcohol abuse can lead to dependence and addiction where people suffer withdrawal symptoms if they are unable to consume it
  • Alcohol causes immediate slowing of reaction times and in the long term can cause liver, circulatory and heart disease
• Phototropism


  A growth response in a plant to a one directional stimulus, caused by the release of the hormone auxin
• Types of phototropism


  • Positive phototropism - growth towards light
  • Positive gravitropism - root growth down into the ground with gravity