Coordination and Responses

• Cornea


  refracts light
• Iris


  controls how much light enters pupil
• Lens


  focuses light onto retina
• Retina


  contains light receptors, some sensitive to light of different colours
• Low Light Intensity

  • radial muscles contact + become shorter to pull pupil
  • making it wider to let more light enter from a clear image of retina
• High Light Intensity

  • circular muscles contract + become shorter
  • reduct pupil size and protect the retina from bleaching
• Accommodation


  adjusting for near + distant object
• Accommodation - Near Object

  • ciliary muscles contract
  • suspensory ligaments slack
  • the lens becomes short + fat
• Accommodation - Distant Object

  • ciliary muscles relax
  • suspensory ligaments tighten
  • the lens becomes long + thin
• Hormones


  chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs
• Adrenaline


  hormone secreted in 'fight or flight' situation and its effects, limited to increased breathing + pulse rate + widened pupils
• Examples of situations in which adrenaline secretion increases

  • riding a rollercoaster
  • bungee jump
• Homeostasis


  maintenance of a constant internal environment
• Negative Feedback


  controls the production of hormones and regulates their own production

  • when the change in hormone level acts as a signal to cancel out that change - when the blood hormone level is low, hormone production is stimulated; when it is high, it is inhibited
• Blood glucose level is monitored+controlled+measured by...

  Pancreas - produce and release different hormones depending on the blood glucose level
• Constant body temperature maintained by:

  INSULATION:

  • provided by fatty tissue (retains heat)
  • hair becomes erect to trap warm air by contracting the erector muscles

  SWEATING:

  • the water evaporates, giving a cooling effect

  SHIVERING:

  • muscular activity generates heat
• Vasodilation


  when it is hot, arterioles supply blood to the skin surface capillaries, dilate to allow more blood near the skin surface to increase heat loss
• Vasoconstriction


  when it is cold, arterioles which supply blood to skin surface capillaries, constrict to allow less blood near the skin surface to decrease heat loss
• Gravitropism


  a response in which parts of a plant grow towards or away from gravity
• Phototropism


  a response in which parts of a plant grow towards or away from the direction from which light is coming
• Auxin


  • plant hormones or growth substances
  • controls tropisms
  • produced by cells at the tip of the roots + shoots of plants
• Auxin in GRAVITROPISM


  • made in-shoot tip
  • then it diffuses through the plant from the shoot tip
  • auxin is unequally distributed in response to light + gravity
  • auxin stimulates cell elongation
  • (positive gravitropism when the root/shoot moves from the direction of gravity if not, negative gravitropism)
• Auxin in PHOTOTROPISM


  • if the sun shines on the right side of a plant's shoot, auxins accumulate on the dark opposite left side
  • auxins accumulating makes cells on the left side grow faster than cells on the right
  • when the left side of the shoot starts growing faster than the right side, the shoot will start to bend to the right side towards the sunlight