Tropisms in plantsIB MYP Biology: Subtopic test

1. 1
   A sunflower seedling is grown in a pot on a classroom windowsill in Cape Town. After a week its shoot has bent towards the window, while its roots have grown downwards into the soil.

   (a)

   What is the stimulus that causes the shoot to bend towards the window?

   [1 mark]

   • ALight
   • BGravity
   • CWater
   • DTouch

   (b)

   What is the response of the roots growing downwards called?

   [1 mark]

   • ANegative gravitropism
   • BPositive phototropism
   • CPositive gravitropism
   • DNegative hydrotropism

   (c)

   Explain why it is an advantage to the seedling that its shoot grows towards the light.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Auxin is a plant hormone made in the tip of a growing shoot. In an experiment, light shines onto a shoot from one side only.

   (a)

   What effect does auxin have on the cells of a shoot?

   [1 mark]

   • AIt stops them growing
   • BIt makes them elongate (get longer)
   • CIt makes them divide to form roots
   • DIt makes them release water

   (b)

   Where does auxin collect when light shines on the shoot from one side only?

   [1 mark]

   • AOn the lit side
   • BOnly in the roots
   • CEvenly on both sides
   • DOn the shaded side

   (c)

   Explain how the movement of auxin makes the shoot bend towards the light.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates whether cress seedlings respond to light. She grows 20 seedlings in each of two identical boxes kept at the same temperature and given the same amount of water. Box 1 has a small hole in one side, so light enters from one side only. Box 2 is lit equally from all sides. After five days she measures how far each shoot has bent from the vertical. The mean angle was 38 degrees in Box 1 and 3 degrees in Box 2.

   (a)

   State a testable hypothesis for this investigation, with a scientific reason, and identify the independent and dependent variables.

   [3 marks]

   (b)

   Evaluate how well the results support the hypothesis, and suggest one improvement to the method.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In a school garden in Nairobi, a bean seed was planted lying on its side in a pot kept in the dark. After four days the root has curved downwards and the shoot has curved upwards. Elsewhere in the garden, the roots of an acacia tree have grown towards a leaking underground water pipe. The gardener is now considering replacing the sprinklers, which water the soil surface every day, with buried drip pipes that supply water deeper in the soil.

   (a)

   Explain how the root and the shoot of the bean seedling respond to gravity, and name the response shown by the acacia roots.

   [6 marks]

   (b)

   Discuss whether the school should replace the sprinklers with buried drip pipes. Reach a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions