Habituation and the nervous systemEdexcel International A Level Biology: Subtopic test

1. 1
   A student taps the shell of a pond snail once every 20 seconds. At first the snail withdraws into its shell each time. After about a dozen taps it no longer withdraws, although the taps are exactly the same.

   (a)

   Which term describes the loss of the snail's response to the repeated tapping?

   [1 mark]

   • AHabituation
   • BSensitisation
   • CAdaptation of the receptor
   • DMuscle fatigue

   (b)

   Why is habituation advantageous to the snail?

   [1 mark]

   • AIt makes the snail's muscles stronger
   • BIt increases the sensitivity of its receptors to touch
   • CIt prevents the snail from ever responding to touch again
   • DIt avoids wasting energy on harmless stimuli, so it can respond to new stimuli that may be dangerous

   (c)

   Suggest how the student could show that the loss of response is due to habituation and not to the muscles of the snail becoming tired.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A barefoot walker treads on a sharp stone and pulls her foot away immediately. A few minutes later she notices that her heart is still beating fast and she feels shaky.

   (a)

   Which of the following is part of the central nervous system?

   [1 mark]

   • AThe sensory neurone in her foot
   • BThe motor neurone supplying her leg muscle
   • CThe spinal cord
   • DThe nerve running down her leg

   (b)

   Which statement correctly compares hormonal coordination with nervous coordination?

   [1 mark]

   • AHormonal responses are faster and shorter lasting
   • BHormonal effects are slower and longer lasting
   • CHormones travel along neurones to their target cells
   • DHormones act on one muscle only

   (c)

   Compare the speed and duration of her foot withdrawal with those of the response that kept her heart rate high, and explain the differences.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A woman walking in a park hears a loud bang. She jumps and her heart rate stays high for several minutes. Two weeks later she lives next to a building site where similar bangs happen every day, and by the end of the fortnight she no longer jumps at them.

   (a)

   Explain how both the nervous system and the hormonal system contribute to her response to the first bang.

   [3 marks]

   (b)

   Explain why she gradually stopped jumping at the bangs near the building site.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A class investigates habituation in pond snails by tapping the shell of a snail at regular intervals and timing how long the snail stays withdrawn into its shell.

   (a)

   Describe how the class should carry out the investigation to obtain valid and reliable results.

   [6 marks]

   (b)

   One snail stayed withdrawn for 38 s after the first tap, 29 s after the fifth tap, 17 s after the tenth tap and 6 s after the fifteenth tap, and did not withdraw after the twentieth tap. Use these data to evaluate whether the snail has habituated.

   [6 marks]

   Total for question 4: 12 marks

End of questions