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A2 Biology OCR June 2015 Revision Thread

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Reply 1480

bbadonde2

Original post by Maham88

what detects low and high glucose levels in the blood ?

The alpha and beta cells in the islets of langerhans

Reply 1481

E_149

Original post by maisie__x

1. The asending limb is permeable to sodium chloride ions, these leave the tubule by diffusion at the bottom and further up by active transport and are reabsorbed into the tissue fluid.

2.Because there is now a higher concentration of sodium and chloride in the tissue fluid than in the tubule this creates a concentration gradient between the tissue fluid and tubule fluid.

3. The descending limb is permeable to water but impermeable to sodium chloride. Because of the created concentration gradient, water diffuses out of the descending limb by osmosis and is reabsorbed into the tissue fluid.

4.This creates a concentrated tubule fluid so minimize water loss. As the fluid flows through the collecting duct, more water can be reabsorbed into the tissue fluid and then into blood capillaries by altering the walls permeability to water (this is osmoregulation)

Okay, just written this out. Thank you :smile:

Reply 1482

joshuajh1707

Anybody got any predictions on the paper? been looking but no one is replying

Reply 1483

WishIHadRevised

Original post by domcandrews

Same i'm getting mostly B's,got 2A's so far, I need an A overall aswell but for econ! Just hoping for 2 good papers, but my feeling seems otherwise especially for f215, can just imagine that 8 marker on timber production or something that i'm not interested in like a 9 marker on Galapagos bullshiit. Good luck for medicine, which uni if you don't mind me asking?

Original post by Cara_rose

I've been getting straight A's is there any topic where you've been losing your marks in particular? I would be happy to help :smile:

Thanks that's really nice of you actually, I'll PM you if I find something major haha. :smile:

Reply 1484

Maham88

why is the theoretical max yield of ATP per molecule of glucose hardly reached in aerobic respiration ?

Reply 1485

baffledchick

What's the difference between an ectotherm and endotherm?

Reply 1486

domcandrews

Original post by joshuajh1707

Anybody got any predictions on the paper? been looking but no one is replying

Will be looking over all the papers, making a list of topics of the spec points that haven't come up at all/recently, most likely tomorrow now. But in general I think you should revise everything, just can't tell, Will be tomorrow, when I get time to make a document or something

hope this helps

Reply 1487

domcandrews

Original post by WishIHadRevised

Aw let's hope we get the grades! I'm worried if I just completely misinterpret a 9 marker or do something stupid. :/
I've got an offer from Liverpool which is AAA and I have no back up haha since it was my only offer.

Thanks that's really nice of you actually, I'll PM you if I find something major haha. :smile:

Yeah totally agree, the drop in grade is huge if you do misinterpret something! :frown:

Congrats on the offer firstly, it takes a lot to get a med offer these days! i'm sure you'll get the grades, getting an offer med must be major motivation!!

Reply 1488

joshuajh1707

Original post by domcandrews

Thank you, I have revised everything and was just looking for some extra items to have a good look at and refresh my memory the morning if the exam.

Reply 1489

domcandrews

Original post by baffledchick

What's the difference between an ectotherm and endotherm?

Ectotherm is an organism that relies on external sources of heat to regulate its body temperature whereas an endotherm is an organism that uses internal sources of heat to maintain its body temp

Reply 1490

HyperIntake

Original post by baffledchick

What's the difference between an ectotherm and endotherm?

An endotherm uses internal sources of heat such as that from metabolism/ respiration to maintain its body temperature within strict limits. Examples are birds and mammals

An ectotherm relies on external sources of heat to regulate its body temperature. Examples are arthropods, insects and reptiles

Reply 1491

domcandrews

Original post by joshuajh1707

Thank you, I have revised everything and was just looking for some extra items to have a good look at and refresh my memory the morning if the exam.

Yeah that was exactly my plan, they're obvusly not going to test the whole syllabus, they will weight more towards a few areas, now it's just how accurate we can predict, but yeah good idea to have sound knowledge of all the spec points

Reply 1492

baffledchick

Thank you, both ectotherms and endotherms have physiological and behavioural adaptations right? Eg Ectotherms - lizard expands its ribcage and frilled lizard uses its frill to expand surface area to absorb more heat from the sun? Locusts increase breathing rate to increase water loss when hot?

Reply 1493

loperdoper

Original post by kell123

hi guys, is it worth learning the method for measuring the rate of respiration even though its not included in the spec. many thanks

I would say it's worth being aware of the basics of the method (just in case they throw in an application of knowledge question), although learning it until you can design it perfectly or anything is just a waste of time.