I have a question about hypertonic and hypotonic cells, please help!!?

Question

If a plant cell has a lower water potential than its surrounding environment and if pressure is equal to zero, is the cell hypertonic or hypotonic to its environment? Will the cell gain water or lose water?

Answer 1

Water potential determines the movement of water from one solution to another depending on the combined effect of solute concentration and pressure

ψ=ψp + ψs

where ψ is the water potential
ψp the contribution of pressure
ψs the contribution of osmotic pressure (solute concentration) and it is a negative number (the higher the solute concentration the more negative the value becomes)

The movement of water is always from the solution with the higher water potential to the solution with the lower water potential. Since the cell has lower water potential (regardless of the details about osmotic pressure or outside pressure) it will gain water.

When you have two solutions, 1 and 2 then if #2 is hypertonic you will have 0>ψs1>ψs2

In your case ψ(env)>ψ(cell) but this means
ψp(env)+ψs(env)>ψp(cell)+ψs(cell)

However since you probably mean that ψp=0 MPa (and not the actual pressure;ψp=0 MPa for atmospheric pressure) you have
ψ=ψs. Thus the water potential reflects directly the effect of osmotic pressure, you have ψs(env)>ψs(cell) and the cell has more negative ψs thus higher osmotic pressure thus it is hypertonic.

If you truly mean that pressure is 0 and you are applying a vacuum then ψp(env)<0. I don't know exactly how much the value would be so it is difficult to tell if the cell is hypotonic or hypertonic; remember you would have

ψp(env)+ψs(env)>ψp(cell)+ψs(cell)

so it depends on the values of each component.

Most probably ψp(cell)=0 and if environment is not pure water then ψs(cell),ψs(env)<0 (if it is pure water ψs(env)=0) which means that the above condition boils down to

ψp(env)+ψs(env)>ψs(cell)

and since all numbers are negative (or ψs(env)=0) this condition is met only for ψs(env)>ψs(cell) meaning again that the cell has more solutes and thus it is hypertonic.

Answer 2

I have never heard the term "water potential". I think what you are referring to in osmolarity, or the number of soluble particles in the liquid medium. In salty water, the number of sodium and chloride particles are higher than in fresh water, so water tends to migrate to the area of lower water concentration. In other words, if the osmolarity inside the cell is higher than the surrounding medium, water will tend to flow into the cell to balance the osmolarity of the medium, unless actively or physically prevented. This is called Osmosis, or the flow of water towards an area of lower concentration.

Answer 3

the cell will gain water - it is hypotonic (the cell will swell up due to the extra water)

Answer 4

Here's a cool demonstration of hyper and hypotonic solutions that I think will help you understand the process. They are interactive so you can 'see' the process. It helped my boys (and me!) to get a handle on the concept.

http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

Scroll down to see isotonic, as well!

Answer 5

cell is hypotonic and will need to gain H2O to maintain homeostasis

Answer 6

hypo- gain water

Answer 7

u shouldn't cheat. go do your own homework.