I.  (30) Environmental stimuli and hormonal stimuli regulate the growth and development of plants.   i) Light (450 nm) given from one direction will cause oat shoots to bend towards the light.
ii) When oat shoots are excised and sections (without the apex) are incubated in indole acetic acid (IAA, an auxin) for a few days, the sections are longer than sections incubated in a buffer control.
Auxins are synthesized at the apex.

a) In (ii), why are the sections incubated with +IAA longer than sections incubated without -IAA?  What is mainly responsible for the growth?
 

b)  Two cellular/molecular events were detected:  pH outside the cells drops,
and mRNA of a DNA-binding protein increased.
What do these events mean, and why would these changes result in a difference in growth?  [Address the following in your answer:  How do plants recognize and respond to this hormone?  Propose a model.  ]
 
 
 
 
 
 
 
 
 

c)  In (i)  what growth change would result in bending of shoot towards the light?
 
 

d)  Assuming environmental stimuli can change hormonal levels, propose a model to explain how blue light could cause the bending of the shoot towards the light source.
[Clue:  What biochemical reasons could change hormonal levels in responsive cells?]
 
 
 
 
 
 
 

(e)  Propose an experiment to test your working model that changes in hormonal levels caused the bending of the shoot?  What are the predicted results?
 
 
 
 
 

II. (40)  The development of a seed involves three events:
 |___(1)____|_________(2)__________|___(3 )____|
           0                30                                     100            120 days after flowering
 -(1)  embryo formation, -(2) reserve food accumulation, (3)  onset of dormancy
Mature soybean seeds contain: 37% protein,   17% lipid
     26% carbohydrate (starch)
Soybean seeds have 2-3X more protein than cereal grains.  Where does this protein come from?  Use the questions & table to guide your answer.
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 A. Soybean/in NO3 containing soil B. Soybean/in soil with
                                                                             No Rhizobium   Rhizobium, but no NO3
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I.  N form taken up from environment               _______________ ___________
ii.  N form in (i) is too oxidized, so it is converted to __________ ___________

iii.  Enzyme(s) needed for conversion in (ii) _________________ ____________
      _________________ ____________
iv.  Is there a loss or gain of electrons (iii)? _________________ ____________
What essential substrate(s) is(are) needed? _________________ ____________
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v.  The first amino acid formed from (ii) is Asparagine.
 There are ____(number) C & ____(n) N in one molecule of asparagine.
The structure of asparagine (2 more pts for full pts):
 

vii)  What is the ultimate source of C in asparagine and thus all amino acids and proteins?
Explain.
 

(viii)  N from the environment is taken up by the _________ (organ), and  transported efficiently in the chemical form ________________ to the developing soybean seed via ______________ (tissue and organ).
 
 

x)  What is the function of the following and give a specific example:
-stored protein in the seed:
 

-stored starch in the seed
 

xi)  All the N atoms and C atoms in our bodies come from plants/algae.  True or False.
Briefly explain why for N and for C.
 
 
 
 

III. (30) Lemna, a small aquatic plant, can be grown heterotrophically in the dark by culturing in a petri dish containing sucrose.  Plant grows slowly and is pale yellow.  If plants are given 10 min of 660 nm light every 8 hours, growth rate increases, and rbsS (rubisco Small subunit) mRNA increase.  The response is reversed by 10 min 730 light given right after 660 nm light. rbsS protein increases when higher level of light is given.
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Treatment                                             Growth             rbsS mRNA                 rbsS protein
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1. Complete Dark                                v. slow               0                                  0
2. 10 min 660 nm light, 8 h Dark          fast                       30                              0
   Repeated
3. 10 min 660 nm, 10 min 730 nm, 8 h Dark slow               0                              0
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(a) (4) What molecule senses the light and why?

What is the absorption spectrum (wavelength of light it absorbs) of this molecule?
 

(b)  (6) Why does 660 nm light increase rbsS RNA levels even though 10 min light was followed by 8 h dark?
 
 
 

(c) (6)  if 660 nm light was immediately followed by 730 nm light, why is rbsS RNA not made?
 
 
 

d) ( 8) Propose a model specifically showing how 660 nm light leads to an increase in rbsS RNA?  [rbsS gene is encoded by the _________ (chloroplast or nuclear or mitochondrial) genome.
 
 
 
 
 

(e)  (6) What is the purpose and significance of inducing rbsS RNA?  What is the specific reaction catalyzed by the assembled protein complex?
 
 

(f)  (2) rbsS protein is synthesized in the
 i) chloroplast ,  ii) nucleus iii) cytoplasm or iv) ER