1 / 71

Chapter 33: Plant Responses

Chapter 33: Plant Responses. 33-1 Plant Hormones. 33-2 Plant Movements. 33-3 Seasonal Responses. Revisiting Evolution. Plants have evolved a number of adaptations to their environment that help with their reproduction and survival. Assessing Prior Knowledge.

abbott
Télécharger la présentation

Chapter 33: Plant Responses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 33: Plant Responses 33-1 Plant Hormones 33-2 Plant Movements 33-3 Seasonal Responses

  2. Revisiting Evolution • Plants have evolved a number of adaptations to their environment that help with their reproduction and survival. Assessing Prior Knowledge • Identify stem and leaf structures that may reflect adaptations to allowing movement. • Differentiate between the locations of primary and secondary growth in a plant. Why might each be beneficial in its own way?

  3. 33-1 Plant Hormones I. Groups of Hormones (transported via phloem) • Hormones are chemical messengers that affect a plant’s ability to respond to its environment (e.g., sunlight, gravity, water, nutrients, and temperature). • The effect of a hormone on a “target cell” is influenced by the hormone’s concentration and its interactions with other hormones.

  4. (1) Growth Regulators • Hormones stimulate or inhibit plant growth, and are grouped into five categories: auxins, gibberellins, ethylene, cytokinins, and abscisic acid.

  5. (A) Auxins (e.g., Indoleacetic Acid or IAA, regulate plant growth) • Hormones involved in plant-cell elongation, apical dominance, and abscission; • NOTE: Developing seeds in fruit naturally make IAA which stimulates the development of a fleshy fruit (removing seeds stops development). • Commercial Usage: Kill weeds, stimulate root growth, prevent sprouting of potato tubers, increase the size of fruit, and prevent fruit from falling prematurely.

  6. (B) Synthetic Auxins (Napthaleneacidic Acid or NAA) • Artificially synthesized and are used to promote root formation on stem and leaf cuttings.

  7. (1) Apical Dominance • The inhibition of lateral buds by the presence of a shoot tip (i.e., if NAA is applied to the cut tip of the stem, the lateral buds remain dormant) NOTE: A.D. keeps lateral buds in reserve. By keeping the lateral buds dormant, the stem can use MORE energy to grow taller, enhancing photosynthesis capabilities. (i.e., If the terminal bud is injured, the dormant lateral buds start growing.)

  8. (2) Agent Orange (and 2,4-D) • Auxin used to defoliate jungles in the Vietnam War (NOTE: A non-auxin contaminant in Agent Orange has been cited as causing a number of health problems in exposed people)

  9. (C) Gibberellins • A class of hormones that stimulate ELONGATION and GROWTH (e.g., plants treated will usually cause the plant to grow to a larger than normal height). • Commercial Usage: Increase the size of seedless grapes and stimulate seed germination.

  10. Critical Thinking (1)Suppose a friend who lives in North Dakota gives you some seeds from a plant that you admired when you saw it in your friend’s backyard. You plant the seeds at your home in Georgia, but they fail to germinate. What do you suggest may be preventing the germination of the seeds?

  11. (D) Ethylene (unlike other hormones, a GAS at room temperature) • Hormone responsible for the RIPENING of fruits. (i.e., one bad apple spoils the bunch) • Commercial Usage: Ripen bananas and tomatoes, color ripe citrus fruits, promote the dropping of mechanically harvested fruits, and promote the flowering of pineapples.

  12. Critical Thinking (2) Suppose you placed a green banana in each of several plastic bags, and either placed a ripe pear or a rotting pear with each banana, sealing every bag. What would you hypothesize about the ripening rate of both classes of green bananas?

  13. (1) Ethephon (synthetic solution of ethylene) • Breaks down to release ethylene gas, used to ripen citrus fruits, bananas, melons, and tomatoes. (2) Abscission (promoted by ethylene) • The detachment of leaves, flowers, or fruits from a plant (e.g., cherries and walnuts—harvested with mechanical tree shakers)

  14. Critical Thinking (3)The seasonal loss of leaves by trees and shrubs serves the adaptive advantage of conserving nutrients. What other adaptive advantages might loss of leaves provide?

  15. (E) Cytokinins • Class of hormones that promote cell division in plants; produced in the developing shoots, roots, fruits, and seeds of a plant. NOTE: In tissue cultures, a HIGH auxin-to-cytokinin ratio promotes ROOT formation while a LOW ratio promotes SHOOT formation. In a whole plant, a high auxin-to-cytokinin ratio INHIBITS lateral bud growth, while a low ratio PROMOTES lateral bud growth.

  16. (F) Abscisic Acid (ABA) • Hormone that helps to bring about dormancy in a plant’s buds and maintains dormancy in its seeds. • Also responsible for the closure of plant’s stomata in response to drought.

  17. (G) Other Growth Regulators • Synthetic and geared towards ornamental plants, not agriculture. (1) Growth Retardants • Chemicals employed by utility companies which prevent plant growth (in trees), in order to prevent them from interfering with power lines. • Potted flowers treated with GRs are kept more compact, resulting in stronger stems (easier to ship and resistant to wind damage). • NOTE: Re$earch Avenue? Chemical retardants for the growth of grasses? Mowing once or twice a summer? Golf course maintenance?

  18. 33-2 Plant Movement I. Tropisms (positive or negative) • A plant movement that is determined by the direction of a specific environmental stimulus. EX: Auxin moves into the cells of the SHOOT TIP that are NOT directed toward the light, causing the cells to elongate, which causes the shoot to LEAN toward the light.

  19. (A) Phototropisms (i.e. Heliotropism, initiated by auxins) • Plant movement in response to light coming from one direction. (1) Solar Tracking (maximizing photosynthesis) • Motion of leaves or flowers as they follow the sun’s movement across the sky.

  20. (B) Thigmotropism • Plant’s growth response to touching a solid object. (e.g., tendrils and stems of vines coil when they touch an object; climbing movement)

  21. (C) Gravitropism (auxin regulated) • Plant’s growth response to gravity. (e.g., roots are POSITIVELY gravitropic while stems are NEGATIVELY gravitropic)

  22. Critical Thinking (4)If a whole potato tuber is planted, only one or two buds at one end will sprout. However, if the potato is cut into pieces that each have a bud, all the buds will sprout. Explain why this may be.

  23. (D) Chemotropism • Plant’s growth in response to a chemical (e.g., the growth of a pollen tube in response to chemicals produced by the tube cell and ovule)

  24. II. Nastic Movements (rapid changes in cell water pressure) • Plant movements that occur in response to environmental stimuli BUT that are INDEPENDENT of the direction of stimuli (unlike tropisms). • K+ ions move out of certain cells, causing osmotic movement of water to follow, forcing neighboring cells to shrink (e.g., leaf movements) EX: Nastic movements allow carnivorous plants (i.e, Venus Fly Trap) to trap insects; Also allow “Sensitive Plants” to discourage insect predators.

  25. (A) Thigmonastic Movements • Movement that occurs in response to TOUCHING or shaking a plant. (e.g., Venus Fly Trap and Sensitive Plant folding its leaves)

More Related