1. 11.17.15 Catalyst Which tissues are responsible for photosynthesis?
I will describe plant hormones.

2. EXPERIMENT CONCLUSION RESULTS Figure 39.5
In 1880, Charles Darwin and his son Francis designed an experiment to determine what part of the coleoptile senses light. In 1913, Peter Boysen-Jensen conducted an experiment to determine how the signal for phototropism is transmitted.
EXPERIMENT
In the Darwins’ experiment, a phototropic response occurred only when light could reach the tip of coleoptile. Therefore, they concluded that only the tip senses light. Boysen-Jensen observed that a phototropic response occurred if the tip was separated by a permeable barrier (gelatin) but not if separated by an impermeable solid barrier (a mineral called mica). These results suggested that the signal is a light-activated mobile chemical.
CONCLUSION
RESULTS
Control
Darwin and Darwin (1880)
Boysen-Jensen (1913)
Light
Shaded
side of
coleoptile
Illuminated
Tip
removed
Tip covered
by opaque
cap
covered
by trans- parent cap
Base covered
by opaque shield
Tip separated
by gelatin block
by mica
Figure 39.5

3. Went concluded that a coleoptile curved toward light because its dark side had a higher concentration of the growth-promoting chemical, which he named auxin.
The coleoptile grew straight if the chemical was distributed evenly. If the chemical was distributed unevenly, the coleoptile curved away from the side with the block, as if growing toward light, even though it was grown in the dark.
Excised tip placed
on agar block
Growth-promoting chemical diffuses into agar block
Agar block with chemical stimulates growth
Control (agar block lacking chemical) has no effect
Control
Offset blocks cause curvature
RESULTS
CONCLUSION
In 1926, Frits Went’s experiment identified how a growth-promoting chemical causes a coleoptile to grow toward light. He placed coleoptiles in the dark and removed their tips, putting some tips on agar blocks that he predicted would absorb the chemical. On a control coleoptile, he placed a block that lacked the chemical. On others, he placed blocks containing the chemical, either centered on top of the coleoptile to distribute the chemical evenly or offset to increase the concentration on one side.
EXPERIMENT
Extracted the chemical messenger for phototropism, auxin, by modifying earlier experiments

4. Blame it on the Hormones chemical signals that allow an organism to respond/grow and develop

5. Auxin contributes to phototropism
phototropism - plant moves due to light
cells on one side (the dark side) grow longer
longer stem = turning!
stimulates growth
Is involved in the formation and branching of roots
Period 5 stopped here!

6. “Stump” after removal of apical bud
Cytokinins
Stimulate cell division laterally
“Stump” after removal of apical bud
Lateral branches

7. Hormones move! cytokinins are produced in the roots
auxin is produced at the top of the plant
travel via xylem

8. Gibberellins
In stems
stem elongation, fruit growth, and seed germination

9. Ethylene “One bad apple spoils the bunch” fruit ripening!
aging and death
gaseous form...

10. Abscisic Acid (ABA) slows down growth in preparation for dormancy
also important in wilting
closes stomata during stress

11. Hormones help plants maintain homeostasis
Homeostasis – an organism’s ability to maintain a stable internal environment while the external environment changes

12. Tropism – when an organism responds to the environment’s stimuli
Phototropism - light
Thigmotropism – touch/contact
Gravitropism – gravity

13. Diagram Time. Tomorrow Lab set up Diagrams checked at end of period
Thursday
Human overview
Plant review page
Friday
Plant Quiz.