5.4 Plant hormones (biology only)

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Question 13
Medium

An investigator researched the gravitropic response of young maize (Zea mays) coleoptiles.

Ten coleoptiles were pinned horizontally to a cork backing in each of two separate environmental chambers:

  • Chamber A remained completely stationary throughout the investigation.
  • Chamber B was mounted onto a clinostat that rotated very slowly (approximately 4 revolutions per hour).

Both chambers were maintained at a constant temperature of 22∘C22^\circ\text{C}22∘C in total darkness for 36 hours36\text{ hours}36 hours.

a.

Explain why it was essential to conduct the entire experiment in total darkness.

[1]
b.

Explain the purpose of mounting Chamber B on a slowly rotating clinostat.

[2]
c.

Describe how the orientation of the coleoptiles in Chamber A will differ from those in Chamber B after 36 hours36\text{ hours}36 hours.

[2]
d.

Explain how the plant hormone indoleacetic acid (IAA) causes the specific growth response observed in Chamber A.

[3]

5.4 Plant hormones (biology only) Questions

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