2. I. Phytohormomes  Hormones = signal molecules  (cell to cell communication)  A) Auxins – lengthen shoots  - apical dominance  B) Cytokinins – cell division  - slow aging  (cytokines = class of animal signal proteins)

3.  c) Ethylene - ripen fruit (is a gas)  d) ABA = Abscisic Acid  - close stomata

4. II. Auxin Mechanism  A. Auxin concentration controls gene transcription  B. The genes controlled regulate cell growth and differentiation  C. Auxin only produced in the apical meristem  1. tip of shoot/root  2. areas where cells divide

5.  D. Auxin transported down shoot by  1. Polar transport  2. (much faster than diffusion)  E. Polar because auxin transport proteins only located at the base of the cells.  (at one pole)  

6. III. Acid Growth Hypothesis  A. High concentration of Auxin cause elongation of apical cells (growth)   B. Called Acid Growth  1. high Auxin conc.  2. active transport H + out of cell  3. makes cell wall low pH

7. C. Twofold effects of high H+ conc. in cell wall  1) pressure on cell wall  a) Membrane potential created  (voltage across memb.)  B) Memb. Pot. Induces ion uptake by cell  C) Cell becomes hypertonic  D) Osmosis increases turgor pressure  2) cell wall expands  a) Low pH  b) Activates expansin enzymes  c) expansin breaks crosslinks (H-bonds) btwn cellulose fibers  d) Allows cell wall to expand

9. D) Result = cell elongates (grows)  1) Under uniform light cells grow equally  2) Directional light causes dark side cells to elongate more  3) Phototropism  http://bcs.whfreeman.com/thelifewire/content/c hp38/3802003.html http://bcs.whfreeman.com/thelifewire/content/c hp38/3802003.html  http://bcs.whfreeman.com/thelifewire/content/c hp38/3802002.html http://bcs.whfreeman.com/thelifewire/content/c hp38/3802002.html

10. Auxin concentrations also respond to gravity  http://www.kscience.co.uk/animations/auxin. htm http://www.kscience.co.uk/animations/auxin. htm

11. III. Stomata  A. stoma = opening  B. guard cell = cells on each side of stoma

12. IV. Stomata open/close  A) opening/closing caused by  1. circadian rhythms (no external signal needed)  2. light  3. drought  B) early morning blue light triggers proton pump  1. proton pumps take in K+  2. creates negative water potential inside  3. water flows in  4. cells become turgid  5. stomata open

13.  C) Drought  1. Abscisic acid (ABA) produced  2. ABA opens anion channels in membrane  3. release of anions (Cl-) depolarize cell  4. depolarization opens K+ channels  5. exiting ions increase water potential  6. water exits cell  7. flaccid guard cells close