Organism response to change in internal & external environm

• Stimuli


  Change in internal or external environment
• Types of Stimuli

  • Pain
  • Taste
  • Auditory
  • Proprioception
  • Temperature
  • pH
• Receptors are specialised cells that detect stimuli.
• Sensory neurons carry information from receptor to the CNS (brain/spinal cord)
• Two kinds of communication in the body

  • Hormonal
  • Nervous
• Advantages of Nervous Communication


  Is very quick
• Advantage of Hormonal Communication


  Longer lasting

  Acts on a wider area
• Taxis


  Direct movement in response to an external stimulus
• Kinesis

  Non-directional response to the presence and intensity of an external stimulus
• State advantage of Taxis & Kinesis

  Maintain mobile organisms in optimum environment

  i.e. Kinesis - Woodlice

  Taxis - Worms
• Why do organisms respond to temperature and humidity via kenesis rather than taxis?

  They are less directional stimulus so there often isn't a clear gradient from one extreme to the other
• Postive Taxis


  Moves towards
• Negative Taxis


  Moves away
• Positive Phototaxis

  Moving towards light

  i.e. bacteria that moves towards light
• Worms as a Taxis


  Worms have a negative phototaxis - meaning they do not like light. They move away from light down through the soil (negative gravotaxis)
• Woodlice as Kinesis


  Woodlice like cool damp areas - therefore they move more fast and randomly (non-directional) when in warm dry (unfavourable environment) areas to try get to a cool damp area (favourable environment). One in the favourable environment they slow down and move less randomly(still non-directional), as they want to remain in this environment.
• Tropism 


  Directional response to a stimulus - as a growth rather than a movement
• Shoots are positively phototropic 


  They grow up towards light
• Shoots are Negative gravitropic

  They grow up against gravity
• Roots are negatively phototropic


  They move down away from light
• Roots are positive gravitropism


  They move down with gravity
• what does IAA control


  Cell elongation
• IAA in shoots


  Enhances cell elongation
• IAA in roots

  Inhibits cell elongation
• Older cells and IAA


  IAA only works in new shoots as the cell wall is not fully formed
• Acid Growth Hypothesis


  This suggests that IAA alters the transport of hydrogen ions, to build up concentration of H+ around the cell wall therefore increase the acidity around the cell wall therefore allowing it to expand more easily.
• How does IAA work in shoots


  IAA is produced in the tip. IAA accumulates on the shaded side of the shoot causing this side to elongate faster therefore the shoot grows towards the light

  
• How does IAA work in roots

  IAA accumulates on the shaded side, however here it prevents cell elongation, IAA inhibits growth in the roots, so the side with the lower concentration will grow faster, therefore the root will bend away from the light.
• IAA in roots with gravity

  • Positive geotropism – IAA redistributes to the underside of the root.IAA inhibits growth, so the side with the lower concentration will grow faster, therefore the root will bend towards gravity.

  
• Nervous System First section

  Central Nervous system:

  Brain and Spinal cord

  Peripheral:

  Motor and Sensory
• Second part of the nervous system

  Motor:

  Somatic and Autonomic

  Autonomic:

  Parasympathetic and Sympathetic
• Diagram of Nervous system


  Loak at this

  
• 4 Fs of autonomic NS

  • Fight
  • Flight
  • Feed
  • Mate
• Reflex Arc


  Stimulus —> Receptors —> Sensory Neuron —> Relay Neuron —> Motor Neuron —> Effector —> Response
• Reflex Arc Advantages 


  Rapid, involuntary response – only two synapses speeds up the reaction, as does a lack of decision making

  Protect the body from harm (do not have to be learnt so work from birth onwards)

  Brain is free to carry out other functions at the same time

  Brain does receive messages, but by the time they arrive at the brain the response has already been carried out (brain does sometimes override the reflex)
• The Spinal Cord

  Pairs of neurons 


  sensory and motor enter and leave the spinal cord along its entire length

  
• Stimulus 


  Change in internal or external in environment
• Advantages of responding to the environment


  Responding to the environment increases the chance of survival (find food/water/shelter/mates, move away from predators/toxins etc.)
• Hormones


  • Occurs in multicellular organisms, including animals and plants
  • Long-lasting and generalised
  • Chemicals are transported to target tissue in the plasma
  • Target cells have receptors on their surface
• Nervous System


  Unique to animals

  • Short-lived and localised
  • Uses neurotransmitters
  • Stimulus à Receptor à Co-ordinator à Effector response