Name:__________________ Spring
'02
(10
pts) Answer the following 10 statements T or F.
T 1. Photosynthesis is composed of dark reactions as
well as light reactions.
F 2. Cell walls are made mostly of cellulose.
F 3. Indole acetic acid is a part of the regeneration
cycle of RUBP.
T 4. C4 and
C3 mechanisms in plants are
different forms of photosynthesis.
T 5. Blue light has more energy in it than red light.
F 6. Cobalt is necessary in the water-splitting
reactions of photosynthesis.
T 7. In plants, like animals, there are receptors for
hormones in the plasma membrane.
F 8. Auxin is a second messenger in plants.
F 9. The yield threshold predicts the minimum yields
needed for profit.
T 10. UDPG is required by cellulose synthase to make
cellulose.(2 pts)
11.
The enzyme responsible for a net gain in C is called RUBISCO.
(2
pts) 12. In C4 plants, the enzyme that fixes C in the mesophyll is called PEP Carboxylase.
(2
pts) 13. The meristem at the top of a plant is called an apical meristem.
(2
pts) 14. Cell enlargement consists of either diffuse growth or tip growth.
(2
pts) 15. An organic substance synthesized in one part of the plant and
transported to another part of the plant where it elicits a physiological
response in low concentrations is called a hormone.
(10
pts) 16. Describe the Acid Growth Theory. Can it completely explain the
stimulation of growth by auxin? Why or Why not?
Acid
Growth Theory (1970) by David Rayle and Robert Cleland
Auxin
initiates an acidification mechanism resulting in a lowering of the pH in the
apoplast. Enzymes involved in wall loosening are activated by the lowered pH
resulting in an increased growth rate.
Evidence
for Acid Growth Theory
1. pH
drops in the apoplast after addition of auxin (stimulation of H+-ATPase)
lag
period is 15-20 min after auxin application; similar to growth response
2.
lower pH and also get increase in growth but only last for an hour (lag only 1
min)
3.
Neutral buffer inhibits auxin action
4.
Wall extensibility is stimulated by low pH in isolated cell walls but not auxin
applied directly to isolated cell walls. However, previously treated segments
with auxin and then cell walls isolated showed increased extensibility.
5.
Certain wall-bound enzymes have low pH optima (ie. glycosidases, expansins)
6.
Fussicoccin, a fungal toxin, stimulates acid induced growth
Major Problem with Acid
Growth Theory
Acid
growth is sustained for only an hour (including FC stimulated growth), whereas
auxin-induced growth is often stimulated for up to 12 h.
Other
enzymes involved in polysaccharide
synthesis are stimulated as well.
Auxin
gene regulation
certain
mRNA are increased within 15 to 20 min after auxin application
others
increase 1 to 2 h after application
some
are repressed
Conclusion:
Auxin is capable of acidifying the medium and inducing " acid
growth", but clearly auxin does more and probably stimulates growth in
other ways as well.
(10
pts) 17. As a graduate student, your professor has asked you to study why corn
root hairs grow faster in soils with higher calcium. How would you measure
growth? What factors would you study that regulate root hair growth? Why?
Root
hairs grow by tip growth and are strongly influenced by calcium and exocytotic
processes. One could measure increase in root hair length as a measure of
growth. One should consider all the parameters of the Lockhart equation. Turgor
pressure, hydraulic conductivity, cell wall extensibility, and the yield
threshold of the cell wall. Therefore one should consider the factors that
affect these parameters, such as the influence of calcium on solute transport
(e.g K+), cytoplasmic Ca and exocytosis, synthesis of cell wall materials,
water uptake (water potential gradient and hydraulic conductivity across the
plasma membrane), the influence of Ca on water channels, the pH of the apoplast
and the influence of cell wall loosening enzymes such as expansins.
(10 pts) 18. A new hormone, comonin, has been
discovered. Three bioassays have been proposed to quantify comonin activity. Which
of the following three bioassays would you choose as the best one to use. Why?
B is the best. It is linear and is easily quantified over a shorter period of time. A is hyperbolic and is insensitive above 1 ng/g. Furthermore the measurements have to wait for 7 days for full response. C takes only 2 days like B for its development, but is rather insensitive and nonlinear in response to Comonin.
A. Comonin causes leaves to turn orange. When leaves
are treated with comonin, an easily measured orange pigment is synthesized over
a time course of 7 days.
B. Comonin causes microscopic tumors to develop on
hypocotyls in 48 hours.
C. Comonin causes a swelling in the diameter of the
petiole over two days.
(6 pts) 19. Draw
thylakoid membranes and label two compartments inside and outside the thylakoid
membranes.
Drawing
must include the lumen and the stroma
What molecule
captures light energy at the end of the electron transport chain. What
compartment is it in? NADP+, stroma
What molecule
captures light energy from the proton motive force generated by the electron
transport chain. What compartment is it in? ADP, stroma
(20 pts) 20. What are the differences between a C3 and C4
plant? In what ways do C4 plants
have an advantage over C3 plants?
C4 Plants vs. C3
C4 has Kranz anatomy - german for
"wreath"
Mesophyll
ring with inner bundle sheath ring around vascular bundle
Basic
Components of C4 Pathway
1. Carboxylation phase in C4 (in mesophyll cells)
2. Decarboxylation (in bundle sheath
cells)
3. Photosynthetic carbon reduction
cycle (in bundle sheath cells)
a) carboxylation
b) reduction
c) regeneration
4. Regeneration phase of C4 cycle
C3 plant only has calvin or photosynthetic
carbon reduction cycle and is in all leaf cells excluding the epidermis
Spatial
separation of Carboxylation critical in C4
so that reactions of PEP Carboxylase and Rubisco do not compete with each
other.
additional
ATP cost to convert pyruvate to PEP in C4
5 ATP
and 2 NADPH/CO2 fixed
Higher
water use efficiency and nitrogen use efficiency in C4
[CO2] is = 5000 ppm
PEP
carboxylase faster than Rubisco causing [CO2]
to concentrate
Rubisco
running at CO2 saturation in C4
Uses
less Rubisco in C4 because substrate
more available
Stomata
kept closed more frequently so less loss of water
C4 plants have capability for
photorespiration but high CO2
competes effectively for O2 with
higher affinity for CO2
C3: 400-500g
H2O transpired/gCO2 fixed
C4: 250-300g
H2O transpired/gCO2 fixed
C4 plants haven't taken over the world they
are more temperature sensitive at low temperatures
C4
plants are better than C3 plants in the following ways:
1. Use
less water and are more water use efficient
2. Use
less Rubisco and are more N use efficient
3. Do
not have photorespiration and are
more energy or C use efficient
(10 pts). 21.
Draw a model for auxin transport through several cells.
(10 pts) 22.
Draw the action and absorption spectrums of photosynthesis on the same figure
(you will not be graded on your artistry!!!). Which plant pigment has a similar
absorption spectrum? Indicate the red light drop on your figure.
red light drop
chlorophyll
is the pigment
(4 pts) 23. What two factors are important for
hormone action?
hormone
concentration and tissue sensitivity to the hormone