1. 1
   A student places germinating maize seedlings in a box with a hole in one side, so light only reaches the seedlings from that direction. After three days, the shoots have bent towards the hole. The student is told that auxin, a plant hormone made in the tip of the shoot, is responsible for this response.

   (a)

   Which row correctly describes the distribution of auxin in the shoot tip and its effect on cell growth on the shaded side compared with the illuminated side?

   [1 mark]

   • AMore auxin accumulates on the shaded side, causing faster cell elongation on the shaded side
   • BMore auxin accumulates on the illuminated side, causing faster cell elongation on the illuminated side
   • CAuxin is distributed evenly on both sides, causing equal cell elongation on both sides
   • DMore auxin accumulates on the shaded side, causing slower cell elongation on the shaded side

   (b)

   The student then turns one of the boxes on its side, so the seedlings are lying horizontally in the dark with no light cue at all. Over the next few days the roots of these seedlings grow downwards and the shoots grow upwards, even though there is no light difference between the upper and lower sides. What is this growth response called, and what causes the unequal growth?

   [1 mark]

   • APhototropism, caused by an uneven distribution of auxin in response to gravity
   • BGravitropism, caused by an uneven distribution of auxin in response to gravity
   • CGravitropism, caused by an even distribution of auxin on all sides
   • DHydrotropism, caused by an uneven distribution of water in the growing medium

   (c)

   In the horizontal box, explain why the root bends downwards while the shoot bends upwards, even though auxin accumulates on the lower side of both organs.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A gardener soaks two batches of pea seeds overnight: batch X in plain water, and batch Y in a solution containing a high concentration of the plant hormone gibberellin. Both batches are then sown in identical trays of moist compost and kept at the same temperature. After five days, 95% of batch Y seeds have germinated compared with only 40% of batch X seeds.

   (a)

   Which statement best explains this result?

   [1 mark]

   • AGibberellin causes unequal growth in response to light, so more of the treated seeds germinated
   • BGibberellin controls the ripening of fruit, so more of the treated seeds germinated
   • CGibberellin ends seed dormancy and initiates germination, so more of the treated seeds germinated
   • DGibberellin is the main hormone controlling phototropism, so more of the treated seeds germinated

   (b)

   The gardener wants to repeat the investigation as a valid comparison between batch X and batch Y. Which of these is the most important variable to control so that any difference in germination is caused only by the gibberellin treatment?

   [1 mark]

   • AThe time of day at which the seeds were originally purchased
   • BThe colour of the tray used to hold each batch of seeds
   • CThe gardener's personal opinion about which batch will germinate better
   • DThe species and age of the pea seeds used in each batch

   (c)

   A seed company wants to sell gibberellin-treated seeds to gardeners who often plant late in the season. Suggest two reasons why treating seeds with gibberellin before sale would be commercially useful.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A supermarket imports bananas while they are still green and hard, then ripens them in a sealed ripening room shortly before they are sold. Workers release a gas into the room for 24 hours, after which the bananas turn yellow and soften over the following days.

   (a)

   Name the plant hormone used and describe its role in this process.

   [3 marks]

   (b)

   Explain why supermarkets choose to import bananas while they are green and ripen them locally using this hormone, rather than importing bananas that are already ripe and yellow.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A commercial plant nursery wants to switch from traditional cuttings to tissue culture to mass-produce a rare, disease-resistant strawberry plant, and also wants to control broad-leaved weeds growing in the grass paths between its outdoor growing beds without hand-weeding.

   (a)

   Explain how plant hormones could be used to help the nursery achieve both of these aims.

   [6 marks]

   (b)

   The nursery is considering whether tissue culture and hormone-based weed control are worth adopting, given the costs and risks involved. Evaluate the advantages and disadvantages of using plant hormones in this way, and suggest whether the nursery should go ahead.

   [6 marks]

   Total for question 4: 12 marks

End of questions