BY 124 SI Worksheet 4 (ch 37, 39)
1.
Discuss how a signal transduction pathway works, with light causing a greening response as an example.
2.
Explain the results of the experiment that Darwin & Darwin did on the mechanism of phototropism.
Cut tip off- didn’t bend
Put opaque cap on the coleoptile and it didn’t bend
Transparent cap- bent to the light

Cover over bottom- still bent
Conclusion- there must be something that causes plants to be able to respond to stimulus
3.
Explain how Boysen and Jensen did their experiment and what was concluded from it.
Boysen Jensen showed there was some compound in the tip that moved down stem and gave message
They put a non-permeable layer in the plant (mica) and the message wasn’t able to be given
They put a permeable layer in the plant and the message was given
4.
Fill in the following chart on common plant hormones and their purposes.
Gibberellins
Cytokinins
Auxin
• Mainly causes stem elongation by cell division and cell elongation
• Stimulates fruit set (staying on plant) and fruit development
• Causes embryos to break down starch
(through causing the enzyme alpha amylase to be made
• Seed breaking dormancy
• Stimulate cytokinesis
• Secondary growth over ride apical dominance of auxin coming from the top of plant
Auxin inhibits lateral buds
Auxin also retards leaf abscission
• jumpstarts growth of fruit
Gravotrophism
elongates coleoptile phototrophism fruit jump start (pollen)

Abscisic Acid • Stress hormone
• Causes stomata to close when water is scarce
• Stops primary and secondary growth
• Reduce cell division
Helps maintain dormancy in seeds
4. Discuss how auxins move through a plant.
• Transported by polar auxin transport
• Ph in cell is 7, ph in cell wall is 5
• Auxin in cell has negative charge
• Carrier at base of cell is necessary to get out to cell wall
• Hydrogen ion comen out of cell (pushed by proton pump) to joins auxin,
• Auxin binded to hydrogen moves into cell
• auxin ionizes back to its negatively charged form as soon as it is in the cell
• Auxin moves to bottom of cell where carriers are, cycle repeats