OCR Biology F211 resit - 16th May Watch

Monster Mnch
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#101
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#101
(Original post by aedai)
As for magnification can you just say the ratio between the size of an object and its image?
The degree in which the size of an image is larger than the object itself.

Pretty simple.
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yamamotootsu
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#102
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#102
I'm very confident about this exam
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yamamotootsu
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#103
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#103
Who else is ready for this?
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VSLGS
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#104
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Weird - smooth muscle - does it constrict or contract???

some books say contract, some say constrict

mark scheme says do not accept contract, but allow it some times...???
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abi.tanner
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#105
good luck tomorrow guys. x
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Rory_M
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How come in the textbook it says that water potential doesn't change when tissue fluid leaves the capillaries? Surely if all the liquid leaves but not large proteins etc, the water potential of the blood at the venous end is lower than that of the tissues?
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Rory_M
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(Original post by VSLGS)
Weird - smooth muscle - does it constrict or contract???

some books say contract, some say constrict

mark scheme says do not accept contract, but allow it some times...???
The muscle contracts, the airway is constricted.
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aedai
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(Original post by Rory_M)
How come in the textbook it says that water potential doesn't change when tissue fluid leaves the capillaries? Surely if all the liquid leaves but not large proteins etc, the water potential of the blood at the venous end is lower than that of the tissues?
Well yes. water potential in the venous end is lower so tissue fluid flows into it via osmosis.

I'm a bit confused about what you said at the beginning >.<

Hm one question. When the tissue fluid flows into the capillary at the venous end, does the tissue fluid contain all the metabolic waste from surrounding cells, i.e carbon dioxide? Cause then it makes more sense.
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Rory_M
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Yes it does. If you look on p62 there's a diagram at the bottom showing that water potential is constant throughout... but surely at the point the fluid leaves the blood, the water potential of the blood is lowered?
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zainn
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are the grade boundaries generally lower in re-sit exams? I was told that the top percentage of results achieved help decide the grade boundaries eg better results overall the higher the grade boundaries. Hence since most of the stronger candidates are not resitting because they've achieved good enough grades in January then there'll be weaker candidates this time around so lower results and reduced grade boundaries? please correct me if i'm wrong.
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Rory_M
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Oh think I just worked it out, the water potential is changed by solutes. So the cells and proteins don't affect it, therefore although their concentration is increased the water potential remains the same as any fluid left in the blood still has the same solute concentration. And the tissue fluid loses its solutes but gains the waste from the tissues, so its water potential also remains constant.

In fact the water potential of the blood is always lower than that of the tissues, so the gradient is always in favour of movement into the capillary, however at the arterial end the very high hydrostatic prssure of the blood overrides it. At the venous end the hydrostatic pressure of the blood is much less as it was lowered by loss in volume of blood (tissue fluid leaving) and so the water potential gradient does override it allowing the net flow to be into the capillary. (the hydrostatic pressure of the blood is still slightly higher than the fluid at the venous end but it's a small difference so has little effect).

Thought I best give a full answer to my question in case I had confused anyone - hate getting confused right before the exam
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shamzika
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#112
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OCR is confusing. Is ' a group of cells with a function' good enough to define tissue
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Rory_M
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#113
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(Original post by zainn)
are the grade boundaries generally lower in re-sit exams? I was told that the top percentage of results achieved help decide the grade boundaries eg better results overall the higher the grade boundaries. Hence since most of the stronger candidates are not resitting because they've achieved good enough grades in January then there'll be weaker candidates this time around so lower results and reduced grade boundaries? please correct me if i'm wrong.
Majority of people sitting this in June will not be resits, however that is good as grade boundaries tend to be lower - when loads of people are resitting they're higher because it means loads of people have done it before/have had longer to prepare. Also if you do it in Jan then the only people apart from resits are really clever people who take it early.
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arcticwombats
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(Original post by Rory_M)
Oh think I just worked it out, the water potential is changed by solutes. So the cells and proteins don't affect it, therefore although their concentration is increased the water potential remains the same as any fluid left in the blood still has the same solute concentration. And the tissue fluid loses its solutes but gains the waste from the tissues, so its water potential also remains constant.

In fact the water potential of the blood is always lower than that of the tissues, so the gradient is always in favour of movement into the capillary, however at the arterial end the very high hydrostatic prssure of the blood overrides it. At the venous end the hydrostatic pressure of the blood is much less as it was lowered by loss in volume of blood (tissue fluid leaving) and so the water potential gradient does override it allowing the net flow to be into the capillary. (the hydrostatic pressure of the blood is still slightly higher than the fluid at the venous end but it's a small difference so has little effect).

Thought I best give a full answer to my question in case I had confused anyone - hate getting confused right before the exam
you've just confused the absolute sh*t out of me
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aedai
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(Original post by shamzika)
OCR is confusing. Is ' a group of cells with a function' good enough to define tissue
A group of specialised cells that carry a specific function.


e.g cillia cells - cillated eplithelium which are in the trachea in the lungs :P
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VSLGS
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(Original post by Rory_M)
The muscle contracts, the airway is constricted.
Thank you!!
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shamzika
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(Original post by aedai)
A group of specialised cells that carry a specific function.


e.g cillia cells - cillated eplithelium which are in the trachea in the lungs :P
Thank you!

P.S Reason for confusion: OCR markscheme:

collection / group, of cells (of one or more types) ;
(cells), working together OR with, common / same,
function ;specialised (cells) ; 2 max
-----------------------------------------------------------------------
ACCEPT a group of cells with a function = 2 marks
IGNORE ref similar cells
DO NOT CREDIT differentiated
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shamzika
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I'm just going to keep coming with the questions...

How would you answer this one:

Which processes must occur in a cell during interphase before mitosis can take place? [3]
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Rory_M
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#119
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#119
Protein synthesis/organelle synthesis.
DNA replication.
Cell growth.
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aedai
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#120
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#120
(Original post by shamzika)
I'm just going to keep coming with the questions...

How would you answer this one:

Which processes must occur in a cell during interphase before mitosis can take place? [3]
I'm also going to add
check DNA for errors - prevent mutations happening.
just to be difficult :P
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