13.2.2 Plant Hormones

Question 1

Plant Hormones

Answer 1

• Like animals, plants have regulatory hormones. Some major plant hormones include auxin, gibberellins, ethylene, cytokinins, abscisic acid, and brassinosteroids.
• Plant hormones are involved in a number of various regulatory mechanisms, including direction of growth (tropisms), cell division, cell differentiation, cell elongation, apical dominance (the concentration of growth at the tip of a shoot), senescence (the aging of a plant), fruit growth and development, germination of seeds, growth inhibition, ripening, and abscission (the
loss of leaves in autumn).

Question 2

Some major plant hormones

Answer 2

• Auxins, such as IAA, are produced in plant embryos, young leaves, and shoot apical meristems. Auxins stimulate cell elongation and development of fruit and are involved in apical dominance, phototropism and gravitropism.
• Gibberellins, such as GA3, are produced in embryos, young leaves, and in the apical meristems of buds and roots. Gibberellins are involved in seed germination, flowering, and the development of fruit.
• Ethylene is produced by the tissues of ripening fruits,
  scenescing tissue, and stem nodes. Ethylene promotes leaf abscission and fruit ripening.
• Cytokinins, such as zeatin, are synthesized in roots. They stimulate germination, promote cell division and growth, and delay senescence.
• Abscisic acid is produced in root caps, older leaves, and stems. It is involved in the inhibition of seed germination and growth.
• Brassinosteroids, such as brassinolide, are produced by seeds, fruits, and floral buds. Brassinosteroids function in growth and development.

Question 3

Gibberellins

i. are found in embryos.
ii. are found in young leaves.
iii. promote seed germination and budding.
iv. stimulate flowering.

Answer 3

• i, ii, iii, iv

Question 4

What is a plant tropism?

Answer 4

• It is the direction in which the plant grows

Question 5

Which one of the following is the best definition of a hormone?

Answer 5

• A chemical that regulates an aspect of homeostasis in plants or animals.

Question 6

Which of the following hormones are likely to stimulate bud growth on the stump of a tree?

Answer 6

• cytokinins

Question 7

Produce is often sprayed with __________ in order to promote ripening.

Answer 7

• ethylene

Question 8

Which of the following is not true about cytokinins?

Answer 8

• They promote fruit ripening.