F215 - Revision thread 13th June 2011

Can anyone explain this point of the specification:
"Evaluate the experimental evidence for the role of auxins in the control of apical dominane and the role of gibberellin in the control of stem elongation"

Also, when talking about auxins and apical dominance do we just have to say when the tip is removed, auxin concentrations in the shoot drops and the buds grow because auxins normally inhibit growth of side shoots?

OR do we have to mention about abscisic acid inhibiting bud growth and high concentrations of auxin keeping concentrations of auxin high so when auxin is removed abscisic acid levels drop so buds grow?

This is page 224 of the OCR textbook

auxins aren't the direct cause of bud growth inhibition which is the point of that spread. Auxin levels keep abscicic acid levels high, which keep Cytokinin levels low. once the apex is removed, auxin levels drop (because they're produced there), abscicic acid levels drop, and cytokinin levels can increase, promoting bud growth

gibberellins: they thought gibberellins promoted stem elongation. they took a shoot of a plant that had a mutation so that it couldn't convert Ga20 to Ga1 (i think?) and grafted it onto a plant with a mutation that couldn't produce any gibberellins due to it not having the enzyme necessary to convert ent-Kaurene to GA12-aldehyde.
they found the plant grew tall, as it could use the Ga20 from the shoot grafted onto it which it couldn't use itself.

i ****ing hate this plant ****.

Reply 881

fortunecookie

17

Does anyone know what page the link to the mark scheme for Jan 2011 F215 is on? I cant seem to find it anywhere.

Reply 882

Nirgilis

14

Original post by fortunecookie

Does anyone know what page the link to the mark scheme for Jan 2011 F215 is on? I cant seem to find it anywhere.

http://www.scribd.com/doc/53130830/OCR-F215-Control-Genomes-and-Environment-January-2011-Mark-Scheme

Reply 883

lmfw

1

Original post by wilsea05

auxins aren't the direct cause of bud growth inhibition which is the point of that spread. Auxin levels keep abscicic acid levels high, which keep Cytokinin levels low. once the apex is removed, auxin levels drop (because they're produced there), abscicic acid levels drop, and cytokinin levels can increase, promoting bud growth

gibberellins: they thought gibberellins promoted stem elongation. they took a shoot of a plant that had a mutation so that it couldn't convert Ga20 to Ga1 (i think?) and grafted it onto a plant with a mutation that couldn't produce any gibberellins due to it not having the enzyme necessary to convert ent-Kaurene to GA12-aldehyde.
they found the plant grew tall, as it could use the Ga20 from the shoot grafted onto it which it couldn't use itself.

i ****ing hate this plant ****.

Thanks a lot! I know how you feel, it's four pages in the text book but it seems like a huge topic!!

Reply 884

intellectual1

3

Original post by twelve

Me too! Its going to be a long day...
I have practically filled an A4 notebook with notes on everything. I've basically done my own textbook. But thats only cause I learn by writing it all down and making sense of it that way.

Wow, I've done exactly the same...well we already have a textbook...but Biology contains so much information...writing it out makes it more memorable...especially in bullet point form :smile:

The most annoying thing of all is, that only a few topics from the specification feature in the examination...its all a matter of knowing which topics to focus on...

Reply 885

ekta9

Original post by emma237

I never understood hardy weinberg but worked my way through these questions

http://www.k-state.edu/parasitology/biology198/hardwein.html

and finally understand it! :smile:

Thanks those are really helpful! Finally understand it too!! :biggrin:

Reply 886

Rup

6

Original post by heartskippedabeat

Are your gut feelings usually right? :tongue:

in all honesty, 80% is usually right!

Reply 887

intellectual1

3

Original post by Rup

in all honesty, 80% is usually right!

is your teacher involved in the examining process? :wink:

Reply 888

heartskippedabeat

10

Original post by Rup

in all honesty, 80% is usually right!

Haha, I'll trust you then :smile:

Reply 889

Mcfilly

Would it be possible for someone to teach me about genetic diagrams? with an example? I literally have no idea and don't understand them at all :frown:

Reply 890

lmfw

1

Original post by Mcfilly

Would it be possible for someone to teach me about genetic diagrams? with an example? I literally have no idea and don't understand them at all :frown:

It's quite hard to describe genetic diagrams over TSR. Have you read the examples in the OCR book over and over?
try: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/celldivision/inheritance2.shtml for simple genetic diagrams (monohybird crosses)

or here: http://www.biotopics.co.uk/genes/crosses/gendia.html

Reply 891

Torrresss

Mark Scheme for the specimen paper anyone?

Define gene therapy.

Original post by lmfw

It's quite hard to describe genetic diagrams over TSR. Have you read the examples in the OCR book over and over?
try: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/celldivision/inheritance2.shtml for simple genetic diagrams (monohybird crosses)

or here: http://www.biotopics.co.uk/genes/crosses/gendia.html

thank you x

Reply 894

Mcfilly

you know for the chi squared test - they always give us the formula in the exam.. well for the hardy weinberg principle will they give us the formula for that too?

Reply 895

patev009

what kind of topics are most likely to come up? anyone?

Reply 896

fortunecookie

17

Original post by Kidms001

http://www.scribd.com/doc/53130830/OCR-F215-Control-Genomes-and-Environment-January-2011-Mark-Scheme

Thanks. I found it in the end. Couldn't find it because it was hidden behind about 5 spoilers! Did you post it before?

Reply 897

twelve

13

Original post by Mcfilly

you know for the chi squared test - they always give us the formula in the exam.. well for the hardy weinberg principle will they give us the formula for that too?

I don't think so, but there's only a couple you need to know: p +q = 1 and p^2 +2pq + q^2 =1

If you do maths, just think binomial :smile:

Reply 898

Waqar Y

11

Hmm, on studying whole genomes atm, i've made my whole book from scratch on this a4 whsmith book that i brought.
after i finish biotech today, ecosystems tommorow, behaviour on saturday then just pure reading only on sunday..fun!