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OCR Biology A Exam Thread (Breadth - May 26, 2016 and Depth - June 7, 2016)

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Reply 460

asdfghjkl99

Stressing out, What's new on the spec?

Reply 461

asdfghjkl99

Does the xylem have plasmodesmata?

Reply 462

asdfghjkl99

Original post by plower

Roots- there are two routes: The apoplast pathway where water goes through the cell walls, mostly by diffusion, until it reaches the endodermis cells in root where the path is blocked by a waxy strip called casparian strip, so now it has to go through the Symplast pathway where the water goes through the cytoplasm via osmosis, plasmodesmata connects connects the cytoplasm of plant cells.

Leaves: the water leaves the xylem and moves into the cell mainly by apoplast where it evaporates into the air spaces in the leaf. When the stomata is open, it diffuses out.

Stem: as the water is evaporated, this creates a 'tension' where which pulls more water upwards. Water molecules are cohesive so a whole column of whole water moves too. Also adhesion is partly involved as well since the water molecules are attracted to the walls of xylem vessel, it helps water rise up.

Good luck xo

What about the vacuolar route?

Reply 463

plower

Original post by asdfghjkl99

Does the xylem have plasmodesmata?

No don't think it does, water goes in by osmosis. Vacoular route? Is that in the spec...there'll be multiple choice questions eh

Reply 464

Gogregg

Original post by asdfghjkl99

What about the vacuolar route?

I don't think we need to know the vacuolar route in much detail, just be aware of it.

Original post by Black Rose

I've heard that it comes up in genetics which we learn in 2nd year so I don't think we need to know it but someone please correct me if I'm wrong.

Yes, we do need to know it! You'll get the formula, but we need to work out observed - expected and square it then do some other stuff and compare answer to the critical value at p=0.05.
Observed value is using your null hypothesis (there will be no difference) so your saying there will be the same number for each test

Wishing everyone the best of luck today!

(edited 7 years ago)

Reply 465

M0nkey Thunder

Posted from TSR Mobile

Good luck!

Reply 466

asdfghjkl99

Original post by plower

No don't think it does, water goes in by osmosis. Vacoular route? Is that in the spec...there'll be multiple choice questions eh

Some sources say that the pits in the xylem are plasmodesmata. Confuses me tbh. Thanks though! Good luckkkk

Reply 467

Mia66

Original post by plower

What is that? And why have I not heard of it?

It's when you try to dilute solutions so it has different concentrations, you might be asked to do calculations related to it

Reply 468

tkhanna

What marks are people getting on the specimen approximately. Cuz I'm getting around 38ish and that's just over 50%. I really hope that's at least a C

Reply 469

ACockyDreamer

When does the exam start

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Reply 470

James3000117

Original post by plower

No don't think it does, water goes in by osmosis. Vacoular route? Is that in the spec...there'll be multiple choice questions eh

I cant check the spec right now as im on mobile but in fairly certain that the vacoular route isnt on the spec. There was a question on it on a sample/practice paper but all of the information you needed about it was given in the question. You only need symplast and apoplast.

Also pits are not plasmodesmata, just call them pits in any answers

Reply 471

asdfghjkl99

Would someone mind explaining selective pressure?

Reply 472

millymolly123

Original post by Mia66

It's when you try to dilute solutions so it has different concentrations, you might be asked to do calculations related to it

What are the calculations? Ive not heard of it either.

Reply 473

James3000117

Original post by Black Rose

I've heard that it comes up in genetics which we learn in 2nd year so I don't think we need to know it but someone please correct me if I'm wrong.

You're thinking of the Hardy-Weinberg principle. Gregg explajns chi squared well, just remember when subbing in that fO is observed values and fE is expected values and you should be able to work from there.

Reply 474

Hmb28

Original post by ACockyDreamer

When does the exam start

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1pm like everyone else's :smile:

Reply 475

Hmb28

Original post by mali473

What experiments should we know?
Posted from TSR Mobile

Revise all practicals you have done in class, there's no set experiments we need to learn. My only suggestion would be using a potometer but that came up on the specimen. Good luck

I'm freaking out!!

Original post by Hmb28

1pm like everyone else's :smile:

Mine starts at 1.30pm

Reply 478

MattLS

The chi squared test isn't in any of the text books I have (CGP and the OCR Year 1 and AS Biology). I don't think it comes up in AS. The only tests we've been told are, Standard Deviation, T test, and Spearman's rank correlation coefficient.