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(2 pts) 1. What are the two important factors necessary for an osmotic system?
1. At least two compartments are separated by a semi-permeable membrane
2. Pressure is able to build up in one of the compartments
(2 pts) 2. If the water potential of a cell is -0.2 MPa and the solute potential is -0.8 MPa, what is the pressure potential?
Yw = Ys + Yp
Yp = Yw - Ys = -0.2 MPa - -0.8 MPa = 0.6 MPa
(2 pts) 3. Short-distance water transport occurs by diffusion. Long-distance transport occurs by bulk flow_.
(2 pts) 4. The relative humidity in a closed container at atmospheric pressure is constant. The liquid phase in the chamber has a solute potential of -0.2 MPa at room temperature. What is the water potential of the vapor phase?
Yw = Ys + Yp= -0.2 MPa + 0 MPa = -0.2 MPa
(2 pts) 5. The tonoplast separates the cytoplasm from the vacuole.
(5 pts) 1. What is root pressure? How does it occur?
Root pressure forms when stomata are closed and ions build up in the XYLEM due to continuing ion transport into the xylem. The increase in ions lowers the water potential of the xylem, causing water to flow in from adjacent living cells by osmosis. Since water is nearly incompressible, pressure builds up in the xylem forcing water to move up to and through the hydathodes. This can only happen in small plants a meter or two in height.
(1 pt) 2. A typical tracheid has 256 times the water flux that a typical vessel has. T or F.
(2 pts) 3. Name two methods one could use to measure the solute potential of a leaf.
Any two of the following will do: Pressure volume curve with pressure chamber, vapor-pressure osmometer, Freeze-thaw method with psychrometer, measure water potential and turgor pressure and calculate the difference.
(2 pts) 4. The plasma membrane separates the symplast from the apoplast.
((3 pts) 1. Name three important factors in water transport that are necessary if the Cohesion-Tension theory is correct.
i. driving force
ii. cohesion
iii. adhesion or hydration force
(1 pt) 2. Where is the key water interface that drives water uptake up a tall tree?
cell wall interface inside the leaf
(1 pt) 3. N and P concentrations are very low in marine waters. T or F.
(5 pts) 5. A scientist measures the soil around a bush with a pressure chamber. It takes 0.9 MPa of pressure to make water come out of the soil. He measures the sap of the roots with a vapor pressure osmometer to find that the sap contains 400 mmol kg-1 of solutes. We know that 40 mmol kg-1 equals 0.1 MPa. If the turgor pressure of the root is 0.3 MPa, can the roots take up water from the soil? Below what turgor potential can water be absorbed spontaneously? To get full credit you must show your calculations and rationale (use the back of this paper if you wish).
water potential of the soil = -0.9 MPa
water potential of the root = solute potenial + turgor = -1.0 MPa + 0.3 MPa = -0.7 MPa
solute potential = -(400mmol kg-1 /40 mmol kg-1) X 0.1MPa = -1.0 MPa
The root cannot absorb water from the soil, because the water potential of the soil is lower than the root. The turgor would have to be below 0.1 MPa for the root to absorb water.
(3 pts) 1. List 3 factors which influence ion uptake into the plant from the soil.
root density, ion concentration in soil solution, nutrient supply
(2 pts) 2. What two components of a chemical potential do you have to consider for ions crossing a membrane?
concentration and electric field
(2 pts) 3. Name the two major components of the membrane potential.
H+-ATPase (proton pump) and diffusion potential
(1 pt) 4. The Nernst equation allows one to predict the membrane potential when ion concentrations across a membrane are known and the chemical potentials are at equilibrium. T or F.
(2 pts) 5. In a plant cell, the PO4- concentration is 25 mM in the cytoplasm, would PO4- be taken up actively or passively from normal soil solution concentrations? Why?
Because it is being taken up against both the electric field and concentration gradient (electrochemical potential gradient)
(10 pts). 1. Two plants are K deficient. They are growing in soils that have a K soil solution concentration of 10 µM. Each of them has a Km of 10 µM and a Vmax of 1000 µmol m-2 s-1. Both plants adjust to situation by changing its transporters. Plant A increases its Vmax to 2000 µmol m-2 s-1. Plant B decreases its Km to 5 µM. Which plant will be more successful in taking up K, all other things being equal. Why? (Show your calculations to justify your conclusions.)
This is the same question as #12 on the 1st midterm from last year.
For both plants:
v = (1000 µmol m-2 s-1)(10µM)/ (10µM + 10 µM) = 500 µmol m-2 s-1
For plant A:
v = (2000 µmol m-2 s-1)(10µM)/ (10µM + 10 µM) = 1000 µmol m-2 s-1
For plant B:
v = (1000 µmol m-2 s-1)(10µM)/ (5µM + 10 µM) = 666.7 µmol m-2 s-1
Plant is more successful because it has a faster rate of uptake. It takes up more per hour!
(2 pts) 1. Name two types of tissues found in a leaf.
you need to answer two of the three below:
a) ground tissue
b) epidermal tissue
c) vascular tissue
If you listed phloem and xylem, I gave you credit for vascular tissues.
(10 pts) 2. Define active transport in the thermodynamic sense.
A substance that is transported from a low chemical potential to a higher potential, against its chemical potential gradient is actively transport.
(5 pts) 3. A root hair has a water potential of -0.3 MPa and a solute potential of
-0.8 MPa. If a scientist measured the pressure potential with a pressure probe, how much pressure would he measure?
Yw = Ys + Yp
-0.3 MPa = -0.8 MPa + x
x= 0.5 MPa
(1 pt) 4. It is not possible for stomata to close in the light. F.
(4 pts) 5. What two factors make up the major portion of the membrane potential of the plasma membrane?
diffusion potential and H-ATPase
(10 pts) 6. The membrane potential across the tonoplast is +10 mV. The concentration of Mg2+ in the vacuole is 1 mM. What would the concentration of Mg2+ have to be in the cytoplasm for passive Mg2+ transport from the cytoplasm to the vacuole? Assume that RT/F ln x = 59 log x
10 mV = 59/2 log (x/1)
log x =2(10)/59
x = 2.183
2.183 mM is the equlibrium concentration, therefore the concentration of Mg in the cytoplasm must be greater than 2.183 mM for passive transport.
(10 pts) 7. A scientist measured the uptake kinetics of Cl- in sagebrush. She found that uptake strictly followed Michealis-Menten kinetics (hint: there was no linear phase in uptake). She determined that the Vmax was 1 µmole g-1 h-1 and the Km was 100 µM. What was the rate of uptake of Cl- in the roots if the soil solution had a concentration of 250 µM. Round your value off to the first two significant numbers.
x= Vmax [S]/ (Km + [S]) =1 µmole g-1 h-1 [250 µM]/ (100 µM + 250 µM)
= 0.71 µmole g-1 h-1
(2 pts) 8. What is the endodermis?
The endodermis is an inner tissue (single layer) surrounding the stele which has the casparian strip, which is a suberized substance between cell walls.
(2 pts) 9. Water is transported through the stomatal pore by diffusion.
(4 pts) 10. Name four factors which influence internal ion concentrations in a root cell.
1. efflux
2. influx
3. transport out of the cytoplasm (vacuole, ER, other organelles)
4. energy
5. affinity of transporter
6. membrane potential
I was fairly liberal on this one if you came up with other ideas, but the answers above were what were covered in class.
(10 pts). 11. Draw a schematic diagram of a K+ channel. Why would K+ transport be passive with this kind of transporter?
It would be passive because ions will move through an open ion pore through the membrane, with no barriers, It would move down its electrochemical potential gradient. With an open channel or space within the pore, there is no mechanism to move the ion against it electrochemical potential gradient.
(5 pts) 12. A scientist measures the soil around a bush with a pressure bomb. It takes 1.5 MPa of pressure to make water come out of the soil. He measures the sap of the leaves with a vapor pressure osmometer to find that the sap contains 800 mmol kg-1 of solutes. We know that 40 mmol kg-1 equals 0.1 MPa. If the turgor pressure of the leaf is 0.6 MPa, can the leaves take up water from the soil? Below what turgor potential can water be absorbed spontaneously? To get full credit you must show your calculations and rationale (use the back of this paper if you wish).
water potential of the soil = -1.5 MPa
800 mmol kg-1/ 400 mmol kg-1MPa-1 = 2.0 MPa
water potential of leaf = -2.0 MPa + 0.6 MPa = -1.4 MPa
No, it can not take up water from the soil spontaneously. The turgor must be below 0.5 MPa for water uptake.
(5 pts). 13. Given that 1000 g of water equals 55.508 moles, what is the mole fraction of water for a solution containing 1500 g of sucrose per kg of water. (MW of sucrose is 342. 3 g).
1500 g/ 342.3 g mol-1 = 4.38 moles of sucrose
xwater = 55.508 / (55.508 + 4.38) = 0.92 7
(10 pts). 14. Explain what the chemical potential is and how it can be used in Plant Physiology (give an example of its use).
The chemical potential is the free energy per unit of a substance which can be dependent upon concentration, gravity, electric fields, and pressure. It can be used to predict if a reaction (or transport) can occur spontaneously and in what direction. In water transport, if one measures the water potential of the plant, one can predict if the plant can absorb water from the soil, provided we know the water potential of the soil.
(10 pts). 15. Why does water move from the leaf to the root in the phloem when the water potential in the leaf is more negative than the water potential in the root? Does this indicate that water transport is active in the phloem?
No, it doesn't indicate that water transport is active. There are no membranes between sieve elements in the sieve tube, therefore water moves by mass flow in the phloem which is dependent upon the pressure gradient as defined by Poiseuille's equation.
(10 pts) 16. The year is 2043 A.D. You notice that your "prize-winning" rose is wilting in the backyard on a hot day. You open your plant genetic engineering manual to whip up a new rose plant that can live in your backyard without wilting. Name the possible sub-headings you think you would find in the Chapter called "Ten Commandments for Growing Roses in Dry Arid Climates". Hint: describe factors you could change in the plant so that it would grow without wilting. (Have fun with this one! Be creative!)
Some possible answers:
1. larger root system
2. less stomates
3. waxier leaves
4. narrower leaves
5. more tracheids to vessels
6. more solutes in leaves
7. deeper root system
8. smaller shoots
9. fewer leaves
10. more sensitive stomata to ABA
(2 pts) 1. Photosynthesis can be divided into two different kinds of reactions. What are they?
Light and Carbon (Dark) reactions
(2 pts) 2. Name the two compartments inside and outside the thylakoid membranes.
Stroma and Lumen
(1 pt) 3. What is the reaction center of photosystem I? P700
(2 pts) 4. What molecule captures light energy at the end of the electron transport chain. What compartment is it in?
NADP+, stroma
(2 pts) 5. What molecule captures light energy from the proton motive force generated by the electron transport chain. What compartment is it in?
ADP, stroma
(1 pt) 6. What molecule is the acceptor of an electron from P680*? Pheophytin
(2 pts) 1. Chlorophyll reflects green light and absorbs red and blue light.
(1pt) 2. Photosynthesis is a process that captures the energy from a photon and transfers that energy to NADPH and ATP. In what form is that energy transferred and ultimately captured? an electron
(1 pt) 3. Rubisco has a rapid turnover rate and is also an oxygenase. T or F.
(2 pts) 4. Name the two organelles outside the chloroplast which participate in photorespiration.
mitochondria and peroxisomes
(1 pt) 5. C3 plants regenerate 3 RUBP (ribulose 1,5 bisphosphate) by reshuffling C from 5 G3P (glyceraldehyde-3-phosphate). T or F.
(1 pt) 6. What molecule is the first donor of electrons in photosynthesis? water
(1 pt) 7. Sucrose is a disaccharide molecule containing glucose and galactose. T or F.
(1 pt) 8. The antenna funnels energy to the reaction center.
((1 pt) 1. A plant that reversibly increases in length is said to be growing. T or F.
(2 pts) 2. What enzyme synthesizes cellulose? What part of the cell is it located?
cellulose synthase; plasma membrane
(2 pts) 3. Name two other constituents of the plant cell wall.
pectin, noncellulosic polysacchardes (hemicellulose) or proteins
(1 pt) 4. What is cell wall extensibility?
the RATE at which the cell wall extends which reflects the ease or ability to extend. For example how easy the fibrils and polymers slide along each other or the rate that polymers are cut and reattached
(3 pts) 5. Name 3 phases of the growth cycle of a plant?
lag, exponential (log), linear or senescent
(1 pt) 6. Name one phase in embryogenesis.
early globular, heart or torpedo
(3 pts) 1. Name three things that affect cell elongation
hydraulic conductance, turgor, cell wall extensibility, yield threshold of the cell wall
(2 pts) 2. What two factors determine hormone activity?
concentration of hormone and hormone sensitivity (receptors and signal transduction pathway)
(2 pts) 3. Give the definition of a hormone.
The definition of a hormone is an organic substance synthesized in one part of the plant and transported to another part, which elicits a physiological response in low concentrations.
(3 pts) 4. Name three of the five classical hormones.
auxins, gibberellins, cytokinins, abscisic acid and ethylene
(2 pts) 1. Name two actions of ethylene.
promotes fruit ripening
inhibits growth
(2 pts) 2. What is the definition of a cytokinin.
a substituted adenine that in combination with auxin promotes cell divison
(2 pts) 3. Describe two different actions of gibberellins in plants.
promotes stem elongation
promotes seed germination
(1 pt) 4. High cytokinin/auxin ratios promote shoot development in callus culture.
(1 pt) 5. GA3 is the only form of gibberellin that is found in plants that is considered highly active. T or F.
(2 pts) 6. Name an inhibitor of ethylene. On what does it act upon?
silver, blocks the binding site of the ethylene receptor
Mid-term 2 (Click on link to view exam)
(2 pts) 1. Name two actions of the blue light receptors phot1 and phot2.
stimulates stomatal opening
prevents etiolation, shortens stem growth
(3 pts) 2. Name three different actions of ABA on plants.
promotes stomatal closure
inhibits shoot growth
causes seed and bud dormancy
(2 pts) 3. What two colors of light cause phytochrome to change conformation and activity?
red and far-red light
(3 pts) 4. Name the three classifications of plants which are defined by whether their flowering is responsive to light or not.
day nuetral
short day
long day