OCR Biology F211 Exam - Tues 11'th January 2011

but what if nothing contradicts anything else?

I mentioned about grey areas in my post above (directly above your post), and I appreciate your point, and I'll want to see the exam markscheme for this. However, I will trust my biology teacher, after guiding me to 400/400 at GCSE, and correctly predicting everything on this paper (ie, she said one of the two mark questions word for word, said very unlikely anything on the heart, lymph, or vessels, said a basic mitosis question, a fill in the blanks regarding either the fetal haemoglobin or the bohr ****, and said plant transport would feature heavily - 14/60, more marks than anything else), I think it's fair for me to go with her definition and thoughts.

Agreed. Couldn't have put it any better.

your teacher sounds sick lol
let us know what she predicts for the june paper!

I mentioned about grey areas in my post above (directly above your post), and I appreciate your point, and I'll want to see the exam markscheme for this. However, I will trust my biology teacher, after guiding me to 400/400 at GCSE, and correctly predicting everything on this paper (ie, she said one of the two mark questions word for word, said very unlikely anything on the heart, lymph, or vessels, said a basic mitosis question, a fill in the blanks regarding either the fetal haemoglobin or the bohr ****, and said plant transport would feature heavily - 14/60, more marks than anything else), I think it's fair for me to go with her definition and thoughts.

question: Describe the routes water takes across the cell surface membrane (2 marks).
Answer: it travels via osmosis because it can diffuse through without touching the lipid tails one route if you even call it a route.
Answer 2: it takes the symplast and vacuolar pathways with explanation two clear pathways of water molecules moving across membranes.
this question was so easy because it was practically taken from the book.
Page 73. OCR text book.
How does water move between cells?
When plant cells are touching each other molecules can pass from one cell to another. the water molecules will move from the cell with a higher water potential to the cell with the lower water potential.
if that were the question then YEP osmosis is 100% correct and defining the mechanism of osmosis would probably score the second mark.
What ROUTE can water take *between cells*?- sound familiar?
The apoplast pathway
The symplast pathway
The vacuolar pathway
symplast and vacuolar pathways both go across the cell surface membrane and are two different routes. which sounds more closely related to the question than simply the mechanism of osmosis.
The pathways are not limited to root/endodermis cells as some people state it and if you want to see this for yourself look at the book alarm bells should have been ringing when you specified one route in a question that stated "routes" but yeah you'll probably reply with some flawed argument that i wont be bothered to reply to no offence , but it IS only 2 marks and osmosis could score you one mark.

hey people you know the water potential calculation i got -1668..do i not get the marks coz i didnt round it off?

your teacher sounds sick lol
let us know what she predicts for the june paper!

One mark for plain diffusion/osmosis through the cell membrane, as water molecules are very small. However, the second mark, will be for mentioning channel proteins, as water molecules, however small, are actually charged, and so a channel protein lets through molecules that are charged. Remember that the Phosphate heads are actually hydrophobic, and that there is a chance that a water molecule could hit that and be repelled. As a result, there are channel proteins that open for water molecules to leave.

The apoplast and symplast pathways are irrelevant to the cell surface membrane. They are relevant to how water, taken in at the roots, reaches the xylem cells.

As it happens, I only got the first mark, but think about it, they cannot expect you to explain the apoplastic and symplastic pathways, as well as an explanation of diffusion in two lines and two marks. Even if you somehow managed to fit it in, it is irrelevant because nowhere in the question does it mention that. It mentions cell surface membrane, ie, the plasma membrane, not the symplastic and apoplastic pathways, which go through a number of cells, membranes and plasmodesmata.

my teachers always tell us if it states 2 then you should put 2, because if your first 2 are right, but the 3rd one contradicts it, you won't get any marks

but dude you are explaining the route of water between cells... it wasn't asking tha, it was asking across a single membrane

*******s....my teacher said that they should mark all of it....

but was unsure cos so many on here said otherwise....

methinks I'll get it remarked if it isn't an A

Yes! Like you, I also put simple diffusion/osmosis because although they are polar, water molecules are small. Also like you I didn't get the second mark (I was never even taught that there was a chance water molecules could hit the hydrophilic -you said hydrophobic but I assume you mean hydrophillic, phosphate group heads).

Some of my friends came out of the exam having put the symplast/apoplast pathways but it deliberately said cell surface membrane. Cell surface membranes can be both in animal or plant cells, so for one reason why would the answer be the pathways that are only present in plant cells?

can't argue with what you believe but just stating some things based on what your previous post stated;
Phosphate heads deflecting water molecules-not in spec not in book
Channel proteins pumping water molecules- first ive heard of it and not in spec nor book, aquaporins which i have heard of are not in the spec or book either.
Osmosis- in the spec AND the book
Symplast pathway-in the spec and the book
Vacuolar pathway- Ditto
2 points vs 4 odd make it 3 v 4 since ud have to insert plasmodesma for symplast both relatively large for a 2 mark.
i duno ur teacher but it IS possible u misheard her or she COULD be wrong????? after all specification is by no means nothing to go by alone but something that is not in the specification or the book OCR provides us with? OR the CGP rendition of ocr bilogy? the evidence speaks in volumes im done its a grey area and god knws huz ryt.
edit: a water loving component of the phospholipid deflecting water molecules? MIND RAPE?

because the question was on onion epidermis cells.

Its not in the spec or the book, but bear in mind, that they ask you to apply your knowledge to situations you haven't been in before, and with the knowledge that water molecules are very small and slightly polar, you could have applied that to the 'cell surface membrane', as worded in the question, which has hydrophobic phosphate ends. Im sure I didnt mishear her, she, in fact, said that the apoplast/symplast route was wrong, and irrelevant, although as you said, there is a small chance she herself could be wrong (I really doubt it, I've told you her credentials. She got one of our students to 3rd in the Biology Olympiad last year). Hydrophobic is repelling water, I'm sure? phobia = fear, phyllic = phallus = love?

Again, its a grey area. What I can say is, we can have a bet, in the form that, when the markscheme comes out, and I am right, you can rep me, and if you are right, I'll rep you