Osmosis

Can anyone clarify the definition of osmosis please?

This has caused real confusion as I have just maybe found out that the definition in the science double award B CGP revision guide maybe wrong which means, looking at my paper from the summer, I got the question on it wrong and lost 5 marks.

The definition in the revision guide states: Osmosis is the movement of water molucules through a partially permeable membrane from a region of HIGH water concentration to a region of LOW water concentration.

It must be the other way round musn't it? (LOW to HIGH) as per the markscheme.

If it is then I reckon thousands of people must have lost marks because of it.

Reply 1

i'm no superman

15

The definition in the book is right. If it went the opposite way from low to high it would otherwise be known as active transport.

Reply 2

Zii

13

Nope. It's a HIGH concentration down a concentration gradient to a LOW concentration. A lovely example is when you're in the bath and you get all wrinkly. There's a ****load more water in the bath then there is in your fingers...so...

Reply 3

TheEd

OP

Isn't that diffusion not osmosis though?

Active transport is where the movement of particles is against the concentration gradient of normal diffusion.

Type in: osmosis definition into google and it says from LOW to HIGH. Type osmosis in and it says HIGH to LOW.

I'm confused

Reply 4

Zii

13

Osmosis is diffusion but with water.

Reply 5

James G

6

Osmosis in simple terms is diffusion of water molecules. It's not quite that simple in reality, but for GCSE yes it's diffusion of water (across a differentially permeable membrane or w/e)

Reply 6

billet-doux

14

osmosis is the movement of water molecules from high concentration to low concentration.
its diffusion but in water :smile:

Reply 7

sparkly_woo

2

Osmosis is the movement of water from a high concentration to a low concentration through a semi-permeable membrane.

I rocked my Osmosis coursework in school :biggrin:

Reply 8

TheEd

OP

Yes, it is high to low.

The question confused me as I thought the concentrations that were shown were the water concentrations but if I read the question they were the glucose. Therefore, it was the oppoiste to what I thought.

High Glucose, low water and low glucose, high water. I'll have to remember that should it come up in the resit.

What did everyone get in their coursework UMS?

I got 120/120 :smile:

Reply 9

Kirsty_5X

Osmosis is just a special form of diffusion for water. So yes, it is high to low - just like in diffusion. It is made out to be more confusing that it really is, even my biology teacher couldn't remember what way round it is as the specification confused her!

Reply 10

Kirsty_5X

TheEd

What did everyone get in their coursework UMS?

I got 120/120 :smile:

Full marks - bet your pleased! I have to do an ISA at my school rather than coursework so it part practical, part timed written exam.

Reply 11

Wangers

16

I prefere another definition:

Diffusion of water through a partially permeable membrane, from a less negative water potential to a more negative water potential. With pure water defined as having water potential of zero.

Reply 12

James G

6

Wangers

I prefere another definition:

Diffusion of water through a partially permeable membrane, from a less negative water potential to a more negative water potential. With pure water defined as having water potential of zero.

Yes but that's more detail than is needed for GCSE. And partially permeable isn't the best definition, things like selectively permeable and differentially permeable are preferable.

Reply 13

Wangers

16

James G

Yes but that's more detail than is needed for GCSE. And partially permeable isn't the best definition, things like selectively permeable and differentially permeable are preferable.

**** GCSEs, use this definition and the OP will actually understand the principle properly, which will serve them well after GCSEs.

Reply 14

James G

6

True, but you can't rely on mark schemes, they don't always give credit for details not specified in their syllabus (yes they should do, but mark schemes can be random).

Reply 15

Wangers

16

James G

True, but you can't rely on mark schemes, they don't always give credit for details not specified in their syllabus (yes they should do, but mark schemes can be random).

I don't give a **** about markschemes, you write that definition and it will be marked correct (because I've done it)

Reply 16

bright star

1

James G

Yes but that's more detail than is needed for GCSE. And partially permeable isn't the best definition, things like selectively permeable and differentially permeable are preferable.

that is THE definition, forget detail. that's what it is. i'm sure that's what i wrote at gcse..... and i thought partially permeable was the usual term. i mean selectively/differentially implies some sort of conscious action whereas it's a passive process tha just happens to work so well....

other definitions about concentration just get really confusing because high water concentrations actually means a low solution concentration so it gets all backwards and confused.

Reply 17

Kirsty_5X

piece_by_piece

well done!
& ahh yeah we have to do the ISA!
but its okayy coz we get to do more than one! i got 37/40 in my biology one which is an A*, so that's okay :smile:

X

Yeah it is good that we can submit our best attempts. I got the same mark as you in my biology ISA last year and 36/40 in the chemistry one. I think we are doing three more this year.

Are you doing the AQA syllabus? Our school hasn't been told what the grade boundaries are for the ISA Exam, do you know them? I would guess 36 and above would be an A* though. You need 90% on the module tests to get an A* though which is quite high compared to other exam boards isn't it?

Reply 18

Kirsty_5X

I hope those boundaries are right! Thanks for telling me :biggrin:

Good Luck with You GCSE's by the way.

Reply 19

Kirsty_5X

yupp i am with AQA. I am doing french this year with all my other subjects. I am worried about the french oral exam most. What was it like. I didn't know you could take GCSE's a year early.. did you do it outside of school?

I am really nervous too because i want to study medicine at Uni and GCSEs are one of the things they look at so i hope i do okay. I mean - i am predicted A* for all my subjects and if i got that i would run around screamin and bang my head against a walk :biggrin:

lol

What subjects did you pick as ur choices? X

Osmosis

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