1. 1
   An airline pilot flies overnight from Dubai to New York, crossing eight time zones. For the first few nights after arriving she feels wide awake at local bedtime and very sleepy in the middle of the afternoon. On the advice of a doctor she spends the first hour after waking each morning outdoors in bright daylight.

   (a)

   Which gland secretes the hormone that promotes sleep as part of the circadian rhythm?

   [1 mark]

   • APituitary gland
   • BPineal gland
   • CAdrenal gland
   • DHypothalamus

   (b)

   Which describes the normal daily pattern of melatonin secretion?

   [1 mark]

   • AHigh during the day, low at night
   • BHighest immediately after each meal
   • CConstant throughout the 24 hours
   • DHigh at night, low during the day

   (c)

   Suggest how spending time in bright morning daylight helps her to adjust to the new time zone.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Twenty oat seedlings (Avena sativa) were grown in darkness until their shoots were 3 cm tall. They were then lit from one side only for 6 hours. The student wrote in her notebook that "all the shoots bent towards the light" and also measured the angle of curvature of each shoot with a protractor held against it, recording a mean of 28° with individual values ranging from 15° to 41°.

   (a)

   What is the name of the growth response shown by the shoots?

   [1 mark]

   • APositive phototaxis
   • BNegative phototropism
   • CPositive phototropism
   • DEtiolation

   (b)

   Which statement explains the bending of the shoots?

   [1 mark]

   • AAuxin becomes concentrated on the shaded side, so cells on the shaded side elongate more
   • BAuxin becomes concentrated on the lit side, so cells on the lit side elongate more
   • CAuxin becomes concentrated on the shaded side, so cells on the shaded side divide faster
   • DAuxin moves into the roots, so the shoot stops growing on the lit side

   (c)

   Distinguish between the two types of observation the student made, and suggest one way of improving the precision of her angle measurements.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Short segments were cut from young pea stems just below the shoot tip, so that they contained no source of auxin. Groups of 10 segments were floated for 3 hours in four different solutions and their mean percentage increase in length was measured. Buffer at pH 7.0: 2 %. Buffer at pH 7.0 with auxin: 18 %. Buffer at pH 4.5 without auxin: 16 %. Buffer at pH 7.0 with auxin and an inhibitor that blocks proton pumps in the plasma membrane: 3 %.

   (a)

   Explain how auxin caused the increase in length of the segments in the buffer at pH 7.0 with auxin.

   [3 marks]

   (b)

   Evaluate how well these data support the hypothesis that auxin causes growth by acidifying the cell wall.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student writes: "Plants cannot integrate the growth and activities of their different parts, because they have no nervous system. Coordination of body systems is something only animals can do."

   (a)

   Explain how phytohormones are used to integrate the growth of the roots and shoots of a plant, including the role of auxin efflux carriers.

   [6 marks]

   (b)

   Evaluate the student's claim, comparing integration in animals with integration in plants.

   [6 marks]

   Total for question 4: 12 marks

End of questions