Presentation on Plant Hormones

Slideshow on plant hormones

Notes version of slideshow on plant hormones

Animation of auxin and tropisms

CN, Name:  ____________________________           Section:  __________________              Date:  _____________

MODULE ON PLANT HORMONES [Main reference: Biology, 5th ed., by Campbell et al. (pp. 751-760)]

Due before class begins on DAY 2 (Tues – Sr, Wed – K, Thurs – Li)

FILL IN THE BLANKS. (10 points)

  1. Hormones have two important characteristics: a) they are _______________ _______________ that are produced in one part of the body and transported to another location, and b) only _______________ concentrations are required to cause substantial changes in an organism.
  2. _______________ are growth responses to a given stimulus: they are considered _______________ when they cause an organ to grow towards them and _______________ when they cause an organ to grow away from them.
  3. _______________ is a response to light caused by a _______________ in the growth of the cells on both sides of a plant organ caused by a hormone called _______________.
  4. FW Went made use of a porous block of _______________ that he infused with the suspected growth substance from the _______________. He found that only the stems of blocks placed _______________ showed curvature. This is because the growth substance caused _____________________________________________.
  5. Stem growth and elongation is caused by low concentrations of the hormone _______________ while root growth and differentiation is caused by the hormone _______________.

ANIMATION (5 points)

View the animation at and explain how auxin causes gravitropism and phototropism.                                                                                                                               


  1. Give two examples of how plants respond to stimuli.
  2. Your mother grows beautiful ornamental plants on your condo’s window box. However, she is having problems with the uneven growth of these plants. What advice will you  give her so that her plants can grow in a more even fashion?
  3. Ethylene is a sweetish-smelling gas responsible for the characteristic odor of ripening fruits. Why is the saying that “one rotten apple spoils the whole barrel,” biologically true?
  4. Ornamental flowers from Baguio or Tagaytay are often sprayed with a plant hormone to maintain freshness before they are transported to Manila. Which plant hormone would be most appropriate for this function? Why?
  5. Abscisic acid (ABA) is a stress hormone that causes seed dormancy and inhibits growth. Under which situations would large amounts of ABA be needed by the plant?

GOING FURTHER. (Bonus = + 2 points)

The rapid closing of the makahiya plant (Mimosa pudica) in response to mechanical stimuli is a rapid response that is not caused by hormones. What causes it?

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