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Flashcards in Stimulus Deck (14)
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Importance of reflex

  • avoids damage to tissues;
  • escape from predators;
  • plays a role in homeostasis


How does a pacinian corpuscle produce a generator potential in response to a stimulus 

  • when pressure is applied, it stretches membrane, causing the PC to change shape
  • stretch-mediated sodium ion channels  open
  • this causes sodium ions to enter,
  • this results in depolarisation
  • a generator potential is formed


Why can rod cells allow us to see in dim light

  • several rods are connected to 1 bipolar neurone
  • many generator potential combine (spatial summation)
  • this can then exceed threshold for an action potential;
  • individual generator potentials won't  exceed threshold;


Benefits of having a large fovea

  • High cone cell density on Fovea 
  • Enables high visual acuity
  • As one cone linked to one bipolar neurone;
  • Wider area of clear vision;


Explain the high visual acuity of cone cells

  • Each cone cell connects to 1 bipolar neurone
  • The brain recieves impulse  from each cone cell individually


Define visual acuity

Resolving power, the ability to distinguish close objects


How do plants shoot respond to illumination and explain the benefit of this

  • IAA moves to the shaded area
  • Causes this side to grow faster, leading to positive phototropism 
  • This causes the shoot to bend towards the light source
  • Light is needed for photosynthesis 


How do plants roots respond to gravity?

  • Gravity causes IAA to accumulate at bottom of root, leading to high conc of IAA
  • This inhibits cell elongation on the lower side 
  • Less inhibition on upper side so it grows more
  • This causes the root to bend downwards


Kinesis definition

  • A non-directional response to a stimulus;
  • Results in an increased speed of movement and repeated change in direction
  • Organism keeps until it is in a more favourable environment;


Explain why it takes time for rod cells to recover their sensitivity to light after moving into darkness

  • rhodopsin broken down by light;
  • takes time to resynthesis it;


Similarity/Difference between taxis and tropism

1. Similarity – directional response to a stimulus

2. Difference –Taxis occurs in animals organisms and tropism occurs in plants


Explain the poor visual acuity of rod cells

  • Spatial Summation of rod cells
  • the brain cannot distinguish between impulse from different rod cells 


Benefits of kinesis

  • stays longer stays in favourable conditions ;
  • remains near food source 


Explain trichromatic vision

  • three types of cones cells
  •  each sensitive to different wavelength of light