[Jazzified]

I have seven questions that I need to answer for my biology class, and I'd like to know if my answers appear to be correct.  The questions with the choices are given, and my answer choice is in bold.  Any feedback will be appreciated.  Thanks!

1. Excessive irrigation in arid regions can cause salts to accumulate in the soil. (The water contains low concentrations of salts, but when the water evaporates from the fields, the salts are left behind and thus, concentrate in the soil).  Do you expect that the increasing salinity/saltiness of the soil would have an adverse effect on agriculture?

a. Yes. Salt easily crosses the cell wall/plasma membrane of a plant cell. Having too much salt inside the cell is deleterious to its function.
b. No. We all know that you need to use extensive irrigation in dry regions. Therefore, salt accumulation must not be a problem.
c. Yes. Due to the selective permeability of the cell membrane, water can cross, but salt cannot. When salt concentrations outside the cell rise, water rushes out of the cell causing plasmolysis.
d. No. Due to the selective permeability of the cell membrane, water can cross, but salt cannot. When salt concentrations outside the cell rise, water rushes into the cell causing it to be turgid.
e. No. Salt easily crosses the membrane while water does not. Thus, the salt concentrations inside and outside the cells are able to become isotonic. The plant suffers no adverse reaction.

2. To study the biochemical properties of a proton transporter, researchers monitored the pH of the solution outside of cells that were grown in the absence or presence of added ATP. When ATP was added to the cells, researchers observed that the pH of the solution outside the cell went down. What is a likely explanation for this observation?

a. The proton transporter facilitates passive diffusion across the plasma membrane.
b. The proton transporter facilitates active transport across the membrane.
c. The proton transporter is a co-transporter.
d. The transport of protons across the membrane is an endergonic reaction.
e. The transport of protons across the membrane is an exergonic reaction.
f. Both Choice a and Choice e are right.
g. Both Choice b and Choice d are right.

3.  An artificial cell consisting of an aqueous solution enclosed in a selectively permeable membrane has just been immersed in a beaker containing a different solution. The membrane is permeable to water and to simple sugars such as fructose and glucose, but completely impermeable to disaccharides such as sucrose. The concentrations of the solutes inside the “cell” are as follows: 0.05 M sucrose; 0.01 M fructose and 0.02 M glucose. The concentrations of the solutes outside of the cell are 0.04 M sucrose; 0.01 M fructose and 0.03 M glucose. Which of the following sentences best describes what will happen?

a. Water will move out of the cell
b. Water will move into the cell
c. Fructose and glucose will move into the cell
d. There will be no net movement of solutes
e. There will be not net movement of water

4. A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 16 picograms of DNA per nucleus. Those cells would have __ picograms at the end of the S phase and __ picograms at the end of G2.

a. 16 ... 16
b. 16 ... 32
c. 32 ... 32
d. 32 ... 64
e. 64 ... 64

5. Which of the following does not occur during mitosis?

a. Condensation of the chromosomes
b. replication of DNA
c. separation of sister chromatids
d. spindle formation
e. separation of the centrosomes

6. Which of the following will not affect the shape of an enzyme’s active site?

a. Non-competitive inhibitor
b. pH
c. Temperature
d. Delta G of the reaction

7. For thousands of years, humans have used yeast in brewing, winemaking and baking. What products are generated by baker’s yeast under anaerobic condition?

a. ATP and lactate
b. ATP, alcohol and CO2
c. ATP and NADH
d. CO2 and lactate
e. ATP, alcohol and NADH

[Sev]

2. To study the biochemical properties of a proton transporter, researchers monitored the pH of the solution outside of cells that were grown in the absence or presence of added ATP. When ATP was added to the cells, researchers observed that the pH of the solution outside the cell went down. What is a likely explanation for this observation?

a. The proton transporter facilitates passive diffusion across the plasma membrane.
b. The proton transporter facilitates active transport across the membrane.
c. The proton transporter is a co-transporter.
d. The transport of protons across the membrane is an endergonic reaction.
e. The transport of protons across the membrane is an exergonic reaction.
f. Both Choice a and Choice e are right.
g. Both Choice b and Choice d are right.

If the proton transporter facilitated passive diffusion (a), how would ATP addition affect pH?

[Jazzified]

2. To study the biochemical properties of a proton transporter, researchers monitored the pH of the solution outside of cells that were grown in the absence or presence of added ATP. When ATP was added to the cells, researchers observed that the pH of the solution outside the cell went down. What is a likely explanation for this observation?

a. The proton transporter facilitates passive diffusion across the plasma membrane.
b. The proton transporter facilitates active transport across the membrane.
c. The proton transporter is a co-transporter.
d. The transport of protons across the membrane is an endergonic reaction.
e. The transport of protons across the membrane is an exergonic reaction.
f. Both Choice a and Choice e are right.
g. Both Choice b and Choice d are right.

If the proton transporter facilitated passive diffusion (a), how would ATP addition affect pH?

Oops, the pH would go up.  So the correct answer would only be E, the transport of protons across the membrane is an exergonic reaction, am I right?

[Sev]

2. To study the biochemical properties of a proton transporter, researchers monitored the pH of the solution outside of cells that were grown in the absence or presence of added ATP. When ATP was added to the cells, researchers observed that the pH of the solution outside the cell went down. What is a likely explanation for this observation?

a. The proton transporter facilitates passive diffusion across the plasma membrane.
b. The proton transporter facilitates active transport across the membrane.
c. The proton transporter is a co-transporter.
d. The transport of protons across the membrane is an endergonic reaction.
e. The transport of protons across the membrane is an exergonic reaction.
f. Both Choice a and Choice e are right.
g. Both Choice b and Choice d are right.

If the proton transporter facilitated passive diffusion (a), how would ATP addition affect pH?

Oops, the pH would go up.  So the correct answer would only be E, the transport of protons across the membrane is an exergonic reaction, am I right?

If the proton transporter was passive, ATP would not change membrane permeability to H+.  Hence, I would say the transporter is active (b).
Not sure whether ender/exergonic.  ATP hydrolysis is exergonic if that is what you mean.

[Padfoot]

I agree with Sev for b). 
Endergonic reactions require energy so active transport would be endergonic.  I would go with g).

[Jazzified]

I agree with Sev for b). 
Endergonic reactions require energy so active transport would be endergonic.  I would go with g).

Hmm, okay, I guess I should think that one over.  Thanks for the input from both of you!  How do the other answers look?

[Padfoot]

All the rest look ok to me.   

[Jazzified]

All the rest look ok to me.   

Thanks, does anybody else agree or disagree with any of my answers?

[Yggdrasil]

If you change 2 to g, then they all look right to me.

[Jazzified]

If you change 2 to g, then they all look right to me.

Thank you!