MCB 259: PLANT PHYSIOLOGY 1998, Quiz 4 - October 21

 

Describe the effects of abscissic acid (list at least two):

 

Circle the correct alternatives:
Blue light leads to closing/opening of the stomata.
Increase in turgor in the guard cells leads to closing/opening of the stomata.
Red light that can be used for photosynthesis leads to closing/opening of the stomata.
Increased CO2 concentrations lead to closing/opening of the stomata.
Insufficient water supply (water stress) leads to closing/opening of the stomata.
Increased concentrations of ABA lead to closing/opening of the stomata
Increased activity of the proton pumping ATPase in the plasmalemma leads to closing/opening of the stomata

You place an epidermal strip on a 1:10 dilution of Murashigge Skoog medium (i.e., a very dilute medium for plant tissue culture, this medium alone should not lead to plasmolysis of plant cells).
What behavior of the stomata do you expect if medium also contains 2 M sucrose?
stomata closing or opening
What do you expect if the medium contains 10ÁM ABA.
stomata closing or opening

A secondary active transport system
A) cannot accumulate its substrate inside the cell
B) uses the electrochemical gradient of another ion or co-substrate to accumulate the substrate
C) shows no saturation with respect to the substrate concentration as long as there is a driving force

You measure the K+ concentrations inside and outside a cell. Inside the cell the concentration is 150 mM, outside 1.5 mM. This accumulation inside the cell
A) does prove that K+ ions are actively transported into the cell
B) suggests the presence of a 3Na+/2K+ pumping ATPase
C) might correspond to the electrochemical equilibrium (i.e. when the inside is 120 mV more negative than the outside)
D) points to a K+/H+ cotransport system

 

You detemine that the chloride concentration inside the vacuole is the same as in the cell wall. At the same time you measure that the vacuole is 150mV more negative than the cell wall. These findings indicate that
A) chloride is actively transported across the tonoplast or the plasmalemma or both.
B) chloride is in equilibrium. There is no reason to assume active transport
C) chloride is pumped out of the cell by a Cl- -pumping ATPase.

 

Which of the following transport mechanisms cannot transport a substrate "uphill", i.e. against the electro-chemical gradient for the substrate.
A) cotransport, B) facilitated diffusion, C) primary active transport, D) secondary active transport

Which of the following transport mechanisms does not show saturation with increasing substrate concentrations?
A) cotransport, B) facilitated diffusion, C) diffusion, D) secondary active transport

With respect to the proton motive force accross the plasmalemma of a typical plant cell the contributions of the electrical and the concentration gradient
A) cancel each other, i.e. the force due to the electrical gradient is cancelled out by the force due to the concentration gradient
B) add to each other, ie, both components of the pmf drive the protons back into the cytoplasm
C) the electrical component does not contribute to the overall driving force, because the transport is carrier mediated.

Draw the concentration dependence of a transport that is due to simple diffusion and of a transport system that is carrier mediated. Label your drawing with respect to the axes and indicate the Km and the vmax where appropriate.

 

Extra points: The addition of an inhibitor of the plasmalemma ATPase to a plant cell will lead to a hyperpolarization/depolarization/unchanged membrane potential?
The addition of an uncharged molecule that is transported into the cytoplasm via an proton cotransport system, will lead to a hyperpolarization/depolarization/unchanged membrane potential?
The addition of a negatively charged molecule that is transported into the cytoplasm via an proton cotransport system, will lead to a hyperpolarization/depolarization/unchanged membrane potential?