Vacuole contraction

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joonkimdds

joonkimdds

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The contractile vacuole of Euglena decreases its rate of contraction when the organism,is transferred from fresh water to seawater This is explained by

a. an increase in the osmotic pressure of the environment
b. a decrease in the*osmotic pressure of the environment


I think answer is A but the correct answer is B.

If solute concentration inc, then osmotic pressure inc.
Seawater has higher solute concentration so osmotic pressure of environment increased.

What do you guys think?
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joonkimdds said:
The contractile vacuole of Euglena decreases its rate of contraction when the organism,is transferred from fresh water to seawater This is explained by

a. an increase in the osmotic pressure of the environment
b. a decrease in the*osmotic pressure of the environment


I think answer is A but the correct answer is B.

If solute concentration inc, then osmotic pressure inc.
Seawater has higher solute concentration so osmotic pressure of environment increased.

What do you guys think?
Click to expand...

no answer A is right osmotic pressure is directly related to solute concentration
 
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joonkimdds said:
The contractile vacuole of Euglena decreases its rate of contraction when the organism,is transferred from fresh water to seawater This is explained by

a. an increase in the osmotic pressure of the environment
b. a decrease in the*osmotic pressure of the environment


I think answer is A but the correct answer is B.

If solute concentration inc, then osmotic pressure inc.
Seawater has higher solute concentration so osmotic pressure of environment increased.

What do you guys think?
Click to expand...

Think of osmotic pressure in terms of the pressure that moves water from one region to another. If you put this organism in seawater, which is hypertonic with respect to the internal environment of the organism, then water moves FROM the organism (Lower concentration of solute) INTO the seawater (Higher concentration solute). Since water is moving from inside the organism into the seawater (and not the other way around) then the pressure that moves water in this direction must be greater than the pressure that moves the water in the opposite direction (Osmotic pressure of the environment). In other words, there's a drop in the osmotic pressure of the environment.
 
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joonkimdds said:
are you saying osmotic pressure is inversely proportional to solute concentration?
Click to expand...

Nope, as you mentioned, osmotic pressure is directly proportional to solute concentration. What you're not paying attention to is how water moves, when you put this organism into the seawater. Water moves from the hypotonic solution (organism's internal environment) to the hypertonic solution (seawater). As water moves into the seawater, the solute concentration drops, because you have the same number of solute particles, and your adding more water. When solute concentration of the environment drops, the osmotic pressure drops as well.

This is the whole idea behind osmosis! You start with two environments, where one environment has a higher osmotic pressure. Then water starts moving in the proper direction to lower the osmotic pressure, until an equilibrium is reached.
 
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nze82 said:
Nope, as you mentioned, osmotic pressure is directly proportional to solute concentration. What you're not paying attention to is how water moves, when you put this organism into the seawater. Water moves from the hypotonic solution (organism's internal environment) to the hypertonic solution (seawater). As water moves into the seawater, the solute concentration drops, because you have the same number of solute particles, and your adding more water. When solute concentration of the environment drops, the osmotic pressure drops as well.

This is the whole idea behind osmosis! You start with two environments, where one environment has a higher osmotic pressure. Then water starts moving in the proper direction to lower the osmotic pressure, until an equilibrium is reached.
Click to expand...

Ok so
1) As soon as this organism enters sea water, it's true that osmotic pressure of environment is higher than inside of organism.

2) but as they go to equilibrium, osmotic pressure of inside and outside the organism become the same.

I think these two are right.

I guess you are answering the question based on the transition from 1 to 2 where as I am stuck with the idea that 1 is correct.


But here is what I think. Vacuole contraction is to make sure to pump water outside. If the contraction rate decreased, that means water is exiting to outside automatically so vacuole doesn't need to contract to force the water movement. If we are thinking about the equilibrium, i think vacuole contraction rate will increase again and that's not stated in the problem.


If b. a decrease in the*osmotic pressure of the environment is correct statement then I think increasing rate of vacuole contractile is what the problem should've said but it said decrease in rate of contractile.
 
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joonkimdds said:
Ok so
1) As soon as this organism enters sea water, it's true that osmotic pressure of environment is higher than inside of organism.

2) but as they go to equilibrium, osmotic pressure of inside and outside the organism become the same.

I think these two are right.

I guess you are answering the question based on the transition from 1 to 2 where as I am stuck with the idea that 1 is correct.


But here is what I think. Vacuole contraction is to make sure to pump water outside. If the contraction rate decreased, that means water is exiting to outside automatically so vacuole doesn't need to contract to force the water movement. If we are thinking about the equilibrium, i think vacuole contraction rate will increase again and that's not stated in the problem.


If b. a decrease in the*osmotic pressure of the environment is correct statement then I think increasing rate of vacuole contractile is what the problem should've said but it said decrease in rate of contractile.
Click to expand...

The vacuole contraction rate decreases, because water is spontaneously lost from the body of the organism, so the need for active transport of water decreases. At equilibrium, the contraction rate shouldn't increase, because there is no net movement of water, so there's no need to get rid of any additional water that enters the cell. And yes! You must consider the transition from 1 to 2 in order to answer the question correctly!
 
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One thing you have to keep in mind is that unlike fluid flow, where fluid moves from higher hydrostatic pressure to lower hydrostatic pressure, water moves from lower osmotic pressure (still higher water concentration) to higher osmotic pressure (lower water concentration).

I don't really thing this is a question of equilibrium. When in fresh water, the osmotic pressure is lower outside the cell and water goes from outside to inside down its own concentration gradient, therefore there's a need for removing water by contraction to prevent it from swelling. When it goes to sea water, the outside osmotic pressure is higher, and water still goes down its concentration gradient, from inside to outside, therefore no need for contractions.
 
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Shinpe said:
One thing you have to keep in mind is that unlike fluid flow, where fluid moves from higher hydrostatic pressure to lower hydrostatic pressure, water moves from lower osmotic pressure (still higher water concentration) to higher osmotic pressure (lower water concentration).

I don't really thing this is a question of equilibrium. When in fresh water, the osmotic pressure is lower outside the cell and water goes from outside to inside down its own concentration gradient, therefore there's a need for removing water by contraction to prevent it from swelling. When it goes to sea water, the outside osmotic pressure is higher, and water still goes down its concentration gradient, from inside to outside, therefore no need for contractions.
Click to expand...

That's the explanation that Kaplan gave on the image I posted
 
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Shinpe said:
When it goes to sea water, the outside osmotic pressure is higher, and water still goes down its concentration gradient, from inside to outside, therefore no need for contractions.
Click to expand...

And therefore the answer is A?
 
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Shinpe said:
The answer to your question is A I guess. The image one seems to be the same question and is B. Are you guys looking at the same question???
Click to expand...

yes that's the same question and like i said, the correct answer is B according to the image but we are arguing that maybe the 'real' correct answer is A.
 
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Oh ok, so I guess I was right!!!!
Kaplan made a mistake and switched it.
What my friend has is
A) increase
B) decrease

But then the img says
A) decrease
B) increase

so they knew they made a mistake (from the one i posted) and changed it to what he posted in his img :D
 
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