Chemical control in plantsEdexcel A-Level Biology B: Mind map

Exam questions on Chemical control in plants

1. A maltster prepares barley for brewing by soaking the grains and letting them germinate. During germination the embryo releases gibberellin, which diffuses to the aleurone layer around the starch-rich endosperm. The aleurone cells then make and release amylase. The maltster stops germination by heating the grains once enough starch has been broken down.
   Explain how the production of amylase allows the barley embryo to grow.2 marks
2. A gardener has three identical single-stemmed saplings of a shrub. On plant X she removes the apical bud. Plant Y is left intact. On plant Z she removes the apical bud and immediately applies a paste containing auxin to the cut surface. After two weeks plant X has produced many lateral shoots, whereas plants Y and Z have produced almost none.
   Explain why plant X produced many lateral shoots.2 marks
3. A student investigates the effect of gibberellic acid on amylase production. She cuts barley grains in half and keeps only the halves without an embryo. She places five halves, cut face down, on each of four starch agar plates containing gibberellic acid at 0, 1, 10 and 100 mg dm⁻³. After 48 hours she removes the grain halves and floods each plate with iodine solution. The mean diameter of the clear zone around the grain halves is 0 mm, 6 mm, 12 mm and 14 mm respectively.
   Explain the appearance of the plates after they were flooded with iodine solution, including the plate that contained no gibberellic acid.3 marks