Plant physiology exam quiz and
answers graded A+
(T/F) Because Faraday's constant is used to convert energy in the form of a voltage to Joules/mole,
we can say that a relatively small voltage can have a large impact on the distribution of an ion across
a membrane - ANS✅✅true
(T/F) Because of the natural log function in equations dealing with solute distribution, a linear
change in the membrane potential has an exponential impact on the solute distribution at
equilibrium. - ANS✅✅true
Which of the following can contribute to the membrane potential of a plant cell?
- secondary active transport that couples the proton motive force with the endergonic transport of a
solute
- cations moving out of a cell down a concentration gradient
- negatively charged macromolecules (proteins, nucleic acids) being held inside the cell
- P-type ATPases pumping protons out of the cell at the expense of ATP
- all are correct - ANS✅✅all are correct
If we measure the membrane potential and the concentration of a solute on either side of a
membrane, the Nernst equation will tell us if - ANS✅✅passive or active transport is employed
If a typical plant cell has a higher concentration of nitrate (NO3-) inside the cell than outside the cell,
it is most likely that - ANS✅✅energy was expended to accumulate the anion (an endergonic rxn)
the proton motive force is - ANS✅✅the electrochemical potential of hydrogen ions
The enzyme that converts atmospheric nitrogen to ammonia in the nodules of the rhizobium/plant
symbiosis is - ANS✅✅nitrogenase
The enzyme that converts nitrate to nitrite is - ANS✅✅Nitrate reductase
, Why is NH4+ toxic to all organisms if allowed to accumulate beyond ~0.5 mM? - ANS✅✅At pH 7 in
the cell, some NH4+ + OH-coverts to NH3 + H2O, and the NH3 can freely cross the membrane. At
more acidic pH (e.g., pH 5.5 of the apoplast), NH3+ H+ converts back to NH4+. The end result is the
dissipation of the proton motive force and membrane potential across the membrane.
Glufosinate (not to be confused with glyphosate) is thus a herbicide because it prevents -
ANS✅✅Glutamate + NH4+ → glutamine
After fertilizing, which of the following forms of nitrogen was most likely preferentially used by the
soybeans? - ANS✅✅ammonium (NH4+)
The legume/rhizobium interaction is a mutually beneficial symbiosis important to nutrient cycling in
the environment. If it is beneficial to both organisms, why do not all plants do it? - ANS✅✅-
Creating nodules and the high ATP requirement for N2 fixation is a tremendous drain of
photoassimilate
- The symbiosis is only beneficial to the plant when other forms of nitrogen are not available
The greatest source for fixing molecular nitrogen (N2) to ammonium (NH4+) in terrestrial
environments is - ANS✅✅Biological fixation by prokaryotes
In most environments, the form of nitrogen that is most readily available to plants that do not have
symbiotic relationships with bacteria is - ANS✅✅Nitrate (NO3-)
Write the processes with the correct order of events in the legume-rhizobia symbiotic interaction -
ANS✅✅An isoflavonoid signal from the plant activates the "NOD" operon pathway in the bacteria.
-> The bacteria releases NOD factor (lipochitin oligosaccharide) which is detected by the plant and
stimulates developmental changes in the plant. -> Root hairs start to curl around the bacteria. ->
Localized degradation of the root hair cell wall leads to formation of an infection thread develops
through the root hair to provide a pathway for bacteria to enter the root. -> Cells in the cortex start
to divide to create the physical structure of the nodule. -> Bacteria enter the nodule cells and
differentiate into bacteroides which are in turn found inside a membrane-bound symbiosome, which
resembles an organelle. -> Bacteroides inside the symbiosomes are surrounded by leghemoglobin
which absorbs free oxygen (which is otherwise toxic to nitrogenase)). -> Nitrogenase inside the
bacteroide takes N2 and lots of ATP and hydrogen to make ammonium, which is some plants is
incorporated into amino acids.
negative membrane potential puts the system into - ANS✅✅equilibrium
answers graded A+
(T/F) Because Faraday's constant is used to convert energy in the form of a voltage to Joules/mole,
we can say that a relatively small voltage can have a large impact on the distribution of an ion across
a membrane - ANS✅✅true
(T/F) Because of the natural log function in equations dealing with solute distribution, a linear
change in the membrane potential has an exponential impact on the solute distribution at
equilibrium. - ANS✅✅true
Which of the following can contribute to the membrane potential of a plant cell?
- secondary active transport that couples the proton motive force with the endergonic transport of a
solute
- cations moving out of a cell down a concentration gradient
- negatively charged macromolecules (proteins, nucleic acids) being held inside the cell
- P-type ATPases pumping protons out of the cell at the expense of ATP
- all are correct - ANS✅✅all are correct
If we measure the membrane potential and the concentration of a solute on either side of a
membrane, the Nernst equation will tell us if - ANS✅✅passive or active transport is employed
If a typical plant cell has a higher concentration of nitrate (NO3-) inside the cell than outside the cell,
it is most likely that - ANS✅✅energy was expended to accumulate the anion (an endergonic rxn)
the proton motive force is - ANS✅✅the electrochemical potential of hydrogen ions
The enzyme that converts atmospheric nitrogen to ammonia in the nodules of the rhizobium/plant
symbiosis is - ANS✅✅nitrogenase
The enzyme that converts nitrate to nitrite is - ANS✅✅Nitrate reductase
, Why is NH4+ toxic to all organisms if allowed to accumulate beyond ~0.5 mM? - ANS✅✅At pH 7 in
the cell, some NH4+ + OH-coverts to NH3 + H2O, and the NH3 can freely cross the membrane. At
more acidic pH (e.g., pH 5.5 of the apoplast), NH3+ H+ converts back to NH4+. The end result is the
dissipation of the proton motive force and membrane potential across the membrane.
Glufosinate (not to be confused with glyphosate) is thus a herbicide because it prevents -
ANS✅✅Glutamate + NH4+ → glutamine
After fertilizing, which of the following forms of nitrogen was most likely preferentially used by the
soybeans? - ANS✅✅ammonium (NH4+)
The legume/rhizobium interaction is a mutually beneficial symbiosis important to nutrient cycling in
the environment. If it is beneficial to both organisms, why do not all plants do it? - ANS✅✅-
Creating nodules and the high ATP requirement for N2 fixation is a tremendous drain of
photoassimilate
- The symbiosis is only beneficial to the plant when other forms of nitrogen are not available
The greatest source for fixing molecular nitrogen (N2) to ammonium (NH4+) in terrestrial
environments is - ANS✅✅Biological fixation by prokaryotes
In most environments, the form of nitrogen that is most readily available to plants that do not have
symbiotic relationships with bacteria is - ANS✅✅Nitrate (NO3-)
Write the processes with the correct order of events in the legume-rhizobia symbiotic interaction -
ANS✅✅An isoflavonoid signal from the plant activates the "NOD" operon pathway in the bacteria.
-> The bacteria releases NOD factor (lipochitin oligosaccharide) which is detected by the plant and
stimulates developmental changes in the plant. -> Root hairs start to curl around the bacteria. ->
Localized degradation of the root hair cell wall leads to formation of an infection thread develops
through the root hair to provide a pathway for bacteria to enter the root. -> Cells in the cortex start
to divide to create the physical structure of the nodule. -> Bacteria enter the nodule cells and
differentiate into bacteroides which are in turn found inside a membrane-bound symbiosome, which
resembles an organelle. -> Bacteroides inside the symbiosomes are surrounded by leghemoglobin
which absorbs free oxygen (which is otherwise toxic to nitrogenase)). -> Nitrogenase inside the
bacteroide takes N2 and lots of ATP and hydrogen to make ammonium, which is some plants is
incorporated into amino acids.
negative membrane potential puts the system into - ANS✅✅equilibrium
