Survival and responseAQA A-Level Biology: Subtopic test

1. 1
   A person touches a hot saucepan handle and snatches her hand away before she feels any pain. The response is a simple reflex that uses a three-neurone pathway.

   (a)

   Which sequence shows the correct order of the structures in the reflex arc?

   [1 mark]

   • AReceptor, sensory neurone, relay neurone, motor neurone, effector
   • BReceptor, motor neurone, relay neurone, sensory neurone, effector
   • CEffector, sensory neurone, relay neurone, motor neurone, receptor
   • DReceptor, relay neurone, sensory neurone, effector, motor neurone

   (b)

   Which structure is the effector in this reflex?

   [1 mark]

   • AThe pain receptors in the skin of the hand
   • BThe sensory neurone in the arm
   • CThe relay neurone in the spinal cord
   • DThe muscle that pulls the hand away

   (c)

   Explain why this reflex helps the person to survive.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pea seedling is laid on its side in complete darkness. After two days the root has curved downwards and the shoot has curved upwards. Measurements show that indoleacetic acid (IAA) has moved to the lower side of both the root and the shoot.

   (a)

   On which side of the root and the shoot is the concentration of IAA higher?

   [1 mark]

   • AThe upper side of both
   • BThe lower side of the shoot only
   • CThe lower side of both
   • DThe upper side of the root and the lower side of the shoot

   (b)

   Which statement explains why the root curves downwards?

   [1 mark]

   • AIAA stimulates elongation of the cells on the lower side of the root
   • BThe high concentration of IAA on the lower side inhibits cell elongation, so the upper side grows faster
   • CRoots do not respond to IAA, so they curve because of gravity pulling them down
   • DIAA inhibits elongation of the cells on the upper side of the root

   (c)

   Explain how the movement of IAA causes the shoot to curve upwards.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student uses a choice chamber to investigate the response of woodlice to humidity. The chamber has two halves that can be set to different humidities, with a gauze floor above them. She places 20 woodlice in the centre and counts how many are in each half after 10 minutes. She repeats the investigation five times. The numbers of woodlice in the humid half were 15, 16, 13, 17 and 14.

   (a)

   Describe how the student should set up the choice chamber so that humidity is the only variable that differs between the two halves.

   [3 marks]

   (b)

   Calculate the mean percentage of woodlice in the humid half. Explain how the woodlice distribution is produced by a kinesis, and how this behaviour increases their chance of survival.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Maize seedlings were grown in a box with a small window in one side. After two days the shoots had bent towards the window. In seedlings whose tips had been removed, the shoots did not bend and grew little. In seedlings whose tips were covered with opaque foil caps, the shoots grew straight up. In a second experiment, seedlings were laid on their sides in complete darkness. After two days the shoots had curved upwards and the roots had curved downwards.

   (a)

   Explain how the results of the first experiment show that the tip is involved, and explain how the shoots bend towards the light.

   [6 marks]

   (b)

   Explain how IAA produces the different responses of the shoots and roots in the second experiment, and how each response increases the chance of survival.

   [6 marks]

   Total for question 4: 12 marks

End of questions