1. 1
   A student germinates several maize seedlings in a closed box that has a single small hole cut into one side, so that light only reaches the seedlings from that direction. After 24 hours the student removes the seedlings and observes that each shoot tip has bent so that it is growing towards the hole.

   (a)

   Which statement correctly describes the distribution of auxin in the shoot tip after it has been illuminated from one side for several hours?

   [1 mark]

   • AAuxin concentration becomes higher on the shaded side of the shoot tip than on the illuminated side
   • BAuxin concentration remains equal on both sides of the shoot tip
   • CAuxin concentration becomes higher on the illuminated side than on the shaded side
   • DAuxin is broken down completely on the shaded side

   (b)

   What effect does the uneven auxin distribution described in part (a) have on the cells of the shoot tip?

   [1 mark]

   • ACells on the shaded side elongate more than cells on the illuminated side
   • BCells on the shaded side elongate less than cells on the illuminated side
   • CCells on both sides elongate by exactly the same amount
   • DCells on the shaded side stop elongating altogether

   (c)

   Using your answers to (a) and (b), explain why the shoot tip bends towards the hole in the box.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener sprays a selective weedkiller containing a synthetic auxin onto a lawn to remove broad-leaved weeds without harming the grass. The same week, the gardener takes several stem cuttings from a rose bush, dips the cut end of each cutting into a rooting powder containing auxin, and plants the cuttings in pots of compost.

   (a)

   Which statement best explains why the selective weedkiller kills the broad-leaved weeds in the lawn but leaves the grass unharmed?

   [1 mark]

   • AThe synthetic auxin causes uncontrolled, excessive growth in the broad-leaved weeds that disrupts their tissues, while the grass is far less sensitive to this concentration of auxin
   • BThe weedkiller lowers the pH of the soil so only the weeds are affected
   • CThe weedkiller blocks photosynthesis only in broad-leaved plants
   • DThe weedkiller prevents water uptake only through the roots of the weeds

   (b)

   Why does the gardener dip the cut end of each stem cutting into rooting powder before planting it?

   [1 mark]

   • ATo stimulate the growth of new roots from the cut end of the cutting
   • BTo prevent the cutting from carrying out photosynthesis
   • CTo speed up flower formation in the cutting
   • DTo kill any fungal spores present on the cutting

   (c)

   Describe one commercial advantage to the gardener of using rooting powder to propagate the rose cuttings, compared with growing new rose plants from seed.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A fruit grower manages two crops. In one vineyard, the grower sprays gibberellin onto the flowers of a seedless grape variety before the fruit develops. In a separate store, a batch of tree seeds has failed to germinate after being kept in very dry conditions for a long period, and the grower wants to break their dormancy.

   (a)

   Explain how the grape grower could use gibberellin treatment to produce seedless grapes for sale, and describe why this is commercially useful.

   [3 marks]

   (b)

   Explain how gibberellin could be used to help the dormant seeds germinate, and describe the role gibberellin plays in the process of germination.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A shipping company transports bananas from farms overseas to supermarkets in the UK. The bananas are picked while still green and hard, transported by sea for several weeks, and then treated with ethene gas in a sealed ripening room shortly before being delivered to shops.

   (a)

   Explain the role of ethene in the ripening of fruit, and describe how a shipping company could exploit this to control the timing of fruit ripening for market.

   [6 marks]

   (b)

   Evaluate the use of gaseous ethene treatment to ripen the bananas after transport, compared with allowing the bananas to ripen naturally on the plant before being picked and shipped.

   [6 marks]

   Total for question 4: 12 marks

End of questions