Topic 12 - Learning Objectives

Question 1

1. Describe the general properties of the five plant hormones discussed in class. #remember

Answer 1

• Auxin
• Cytokinin
• Gibberellins
• Abscisic Acid (ABA)
• Ethylene

Question 2

1. a) Identify their sites of production and major functions. #understand

Answer 2

• Auxin:
  
  • Site of Production: Apical meristems, young leaves, and developing seeds.
  • Major Functions: Cell elongation, apical dominance, phototropism, gravitropism, and root development.
• Cytokinin:
  
  • Site of Production: Root tips, developing fruits, and seeds.
  • Major Functions: Cell division and differentiation, delaying senescence, promoting lateral bud growth.
• Gibberellins:
  
  • Site of Production: Young leaves, developing seeds, and roots.
  • Major Functions: Stem elongation, seed germination, fruit growth, and flowering.
• Abscisic Acid (ABA):
  
  • Site of Production: Mature leaves, root caps, and seeds.
  • Major Functions: Inducing dormancy in seeds, promoting stomatal closure during water stress.
• Ethylene:
  
  • Site of Production: Ripening fruits, aging tissues, and wounded areas.
  • Major Functions: Fruit ripening, leaf abscission, and stress responses.

Question 3

2. Explain auxin’s role in phototropism, gravitropism, and root development. #apply

Answer 3

• Phototropism: Auxin promotes cell elongation on the shaded side of the stem, causing it to bend towards the light source.
• Gravitropism: Auxin redistribution in response to gravity regulates cell elongation, causing roots to grow downwards and stems upwards.
• Root Development: Auxin accumulates in root tips, promoting cell elongation and differentiation, and inhibiting lateral root formation.

Question 4

3. Explain the roles of auxin and cytokinin in apical dominance. #apply

Answer 4

• Auxin produced by the apical meristem inhibits the growth of lateral buds, maintaining apical dominance.
• Cytokinin produced in the roots counteracts auxin’s inhibitory effect on lateral buds, promoting their growth.

Question 5

4. Describe the effects of gibberellins on fruit, stems, and seeds. #apply

Answer 5

• Fruit: Gibberellins promote fruit growth and seed development by stimulating cell elongation and division.
• Stems: Gibberellins stimulate stem elongation by promoting cell division and elongation in internodes.
• Seeds: Gibberellins promote seed germination by breaking dormancy and activating enzymes involved in seedling growth.

Question 6

5. Describe the effects of abscisic acid on seeds and leaves. #apply

Answer 6

• Seeds: ABA induces seed dormancy by inhibiting germination and promoting desiccation tolerance.
• Leaves: ABA promotes stomatal closure during water stress to reduce water loss through transpiration.

Question 7

6. Describe the effects of ethylene during stress responses, in senescence, and on fruit. #apply

Answer 7

• Stress Responses: Ethylene production increases in response to environmental stress, promoting senescence and abscission of leaves.
• Senescence: Ethylene accelerates aging and senescence in leaves and flowers, leading to their eventual abscission.
• Fruit: Ethylene stimulates fruit ripening by promoting the breakdown of cell walls and the conversion of starches to sugars.

Question 8

7. List the three stages of cellular signalling. #remember

Answer 8

• Reception
• Transduction
• Response

Question 9

8. Explain how target cells perceive signals using etiolation/de-etiolation as an example. #analyze

Answer 9

• In etiolated plants, lack of light stimulates the production of auxin, promoting stem elongation and inhibition of leaf expansion.
• Upon exposure to light, photoreceptors perceive the signal and activate signaling pathways that lead to de-etiolation, resulting in inhibition of auxin production, promotion of leaf expansion, and chlorophyll synthesis.

Question 10

9. Describe how plants respond to mechanical stimuli. #understand

Answer 10

Plants may respond to mechanical stimuli by altering growth patterns, such as thickening stems or developing thorns or tendrils for support.

Question 11

10. Summarize defence mechanisms that plants have to protect themselves against herbivores. #understand

Answer 11

• Production of toxic compounds or secondary metabolites.
• Physical defenses like thorns, spines, or tough leaves.
• Induction of defensive signaling pathways in response to herbivore attack.
• Production of volatile organic compounds to attract predators of herbivores.

Question 12

Hormone

Answer 12

Chemical messengers produced by living organisms that regulate various physiological functions and behaviors within the organism.

Question 13

Auxin

Answer 13

A type of plant hormone that controls growth and development, including cell elongation, root formation, and apical dominance.

Question 14

Cytokinins

Answer 14

Plant hormones that promote cell division and growth, influencing processes like shoot and root development, chloroplast formation, and delay of senescence.

Question 15

Gibberellins

Answer 15

Plant hormones that regulate various aspects of plant growth and development, including stem elongation, seed germination, and flowering.

Question 16

Abscisic acid

Answer 16

A plant hormone involved in stress responses and growth regulation, particularly in seed dormancy, leaf abscission, and stomatal closure.

Question 17

Ethylene

Answer 17

A gaseous plant hormone involved in various physiological processes, including fruit ripening, leaf and flower senescence, and response to stress.

Question 18

Acid-growth hypothesis

Answer 18

A theory explaining cell elongation in plants, suggesting that auxin induces proton pumping into the cell wall, lowering pH and activating enzymes that loosen the cell wall, allowing for expansion.

Question 19

Expansin

Answer 19

Proteins involved in cell wall loosening and expansion, facilitating cell elongation and growth.

Question 20

Lateral transport

Answer 20

The movement of substances (such as nutrients, hormones, or water) across a plant from one region to another, often mediated by vascular tissues like xylem and phloem.

Question 21

Phototropism

Answer 21

The growth response of plants towards or away from light, allowing them to optimize light absorption for photosynthesis.

Question 22

Gravitropism

Answer 22

The growth response of plants in relation to gravity, causing roots to grow downwards (positive gravitropism) and shoots to grow upwards (negative gravitropism).

Question 23

Apical dominance

Answer 23

The phenomenon where the terminal bud of a plant suppresses the growth of lateral buds, controlling the overall shape and growth pattern of the plant.

Question 24

Aleurone

Answer 24

A layer of cells found in the outermost portion of the endosperm in many seeds, involved in the production of enzymes during germination.

Question 25

Triple response

Answer 25

A set of growth responses in plants to avoid obstacles or navigate through them, involving a decrease in stem elongation, increased stem girth, and curvature.

Question 26

Senescence

Answer 26

The process of aging in plants, involving the programmed deterioration and death of cells, tissues, or entire organs.

Question 27

Signal transduction

Answer 27

The process by which a cell converts an extracellular signal, such as a hormone binding to a receptor, into a specific cellular response.

Question 28

Etiolation

Answer 28

The pale and elongated growth of plants that develop in the absence of light, often occurring when seedlings grow in darkness.

Question 29

De-etiolation

Answer 29

The process by which plants resume normal growth and development after being exposed to light following a period of etiolation.

Question 30

Thigmomorphogenesis

Answer 30

The process by which plants adapt their growth and development in response to mechanical stimuli, such as wind or touch, leading to changes in morphology and physiology.