Osmosis hypothesis?

I got my stimulus and it says that:
Jen adds her carrots to water and John adds his to a salt solution, and it later changes in mass.

What actually happens? I'm confused. Which goes higher in mass and which goes lower in mass and why?!? I understand if its a sugar solution but is a salt solution the same thing?

Please and thank you :smile:

Reply 1

Spectral

8

Nice question!

You're absolutely correct its about osmosis. So which will gain mass and which will lose mass, and why? I'll hopefully try my best to answer that.

Scenario 1:
1. Puts carrot into water
Scenario 2:
1. Puts carrots in salt solution

This is all about water potential/osmosis, and the definition of osmosis is the net movement of water molecules from a region of high water potential to a region of lower water potential down a water potential gradient until dynamic equilibrium is reached.

The water potentials relative to each other is as follows:
Highest: Water
Middle: Carrot
Lowest: Salt

This means that for scenario 1 - water moves from the surrounding water solution into the carrot, hence the carrot will increase in mass due to the water moving in (the carrot is hypertonic relative to the solution).
For scenario 2 water moves from the carrot into the surrounding solution, hence the carrot will lose mass as it loses water (the carrot is hypotonic relative to the solution).

Salt and sugar the same thing? As a solute - absolutely! Having salt in a solution will decrease its water potential, and so the surrounding solution will create a water potential gradient favouring the net movement of water out of the carrot into the salt solution until it all nicely balances up. Although, to balance it up, the carrot will need to lose quite a lot of water, and so it will become lighter as a result.

Hope I've helped a tiny bit! Note that I'm an A level student myself, so take what I write with a pinch of salt! (or if you like, sugar is fine too!)

If you have any further questions please feel free to ask

(edited 8 years ago)

Reply 2

Sakura-Sama

OP

9

Original post by Spectral

Nice question!

You're absolutely correct its about osmosis. So which will gain mass and which will lose mass, and why? I'll hopefully try my best to answer that.

Scenario 1:
1. Puts carrot into water
Scenario 2:
1. Puts carrots in salt solution

This is all about water potential/osmosis, and the definition of osmosis is the net movement of water molecules from a region of high water potential to a region of lower water potential down a water potential gradient until dynamic equilibrium is reached.

The water potentials relative to each other is as follows:
Highest: Water
Middle: Carrot
Lowest: Salt

This means that for scenario 1 - water moves from the surrounding water solution into the carrot, hence the carrot will increase in mass due to the water moving in (the carrot is hypertonic relative to the solution).
For scenario 2 water moves from the carrot into the surrounding solution, hence the carrot will lose mass as it loses water (the carrot is hypotonic relative to the solution).

Salt and sugar the same thing? As a solute - absolutely! Having salt in a solution will decrease its water potential, and so the surrounding solution will create a water potential gradient favouring the net movement of water out of the carrot into the salt solution until it all nicely balances up. Although, to balance it up, the carrot will need to lose quite a lot of water, and so it will become lighter as a result.

Hope I've helped a tiny bit! Note that I'm an A level student myself, so take what I write with a pinch of salt! (or if you like, sugar is fine too!)

If you have any further questions please feel free to ask

Thank you so much! It was really thorough and was easy to understand :smile:

I just have one question; when the water is going out of the carrot it needs to become isotonic right?

Reply 3

Spectral

8

Another great question!

Although I'm not sure quite what to make of that question (failure of my part). I think either you mean:
1. If the carrot is isotonic to the solution water will leave the carrot
2. Water leaves the carrot until it becomes isotonic [personally I think you meant this one]

I would like to clarify one thing though that is a bit conceptually difficult. The one thing I want to clarify is that water molecules are moving continuously between the carrot and solution, whether or not there is a concentration gradient. Its a 'dynamic' system, its not like the water molecules are stuck in one place, they are free to move all over the place. (and between if it is a partially, permeable membrane which a carrot has)
What we mean when we say water moves down a concentration gradient/water potential gradient is that it is a net movement from one place to another. The word net is really key: essentially it means 'most' of the water is moving in that direction. An analogy is like crossing a road: perhaps most people will be trying to cross the road to get to a shopping centre, but of course there may still be other people on the other side of the road leaving the shopping centre. Even though there is a net movement of people crossing the road into the shopping centre, there are still some people crossing the road the other way.

So for potential question 1:
The answer is yes, water will move, it is always moving. However isotonic, meaning same concentration, means theres no net movement of water molecules from carrot to solution or vice versa. This means there is no osmosis occurring.

For potential question 2:
The answer is a yes and no. If you put the word 'net' in front of water, absolutely; the net movement of water will continue down the concentration gradient until it finally evens it out (carrot becomes isotonic to solution).

Maybe I should just quickly clarify how the word isotonic should be used. We can't really call something 'isotonic' by itself, its a word used to compare two things (like calling something big, an elephant is big compared to a mouse, but is it big compared to a black hole?)
So when we say isotonic, we need to say 'X is isotonic with regards to Y' meaning that 'solution X is of the same concentration as solution Y'
Since osmosis is the net movement of water, and if there's no gradient, there's no net movement (still movement though!), so there is no longer the process of osmosis occurring.

I'm sorry if I haven't answered the question you asked, please feel free to re-ask it (or hopefully someone more competent than I can answer it). Hope you've learnt at least a bit though in this weirdly convoluted explanation!

(edited 8 years ago)

Reply 4

username2427341

19

Original post by Sakura-Sama

I got my stimulus and it says that:
Jen adds her carrots to water and John adds his to a salt solution, and it later changes in mass.

What actually happens? I'm confused. Which goes higher in mass and which goes lower in mass and why?!? I understand if its a sugar solution but is a salt solution the same thing?

Please and thank you :smile:

Haha, this is your biology controlled assessment :biggrin: