A2 Biology OCR June 2015 Revision Thread

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Can someone please explain pollarding and coppicing?
Thanks

coppicing is when you cut the trees close to the ground so promote regrowth
pollarding is V simular, but its done further away from the ground higher up in the tree to prevent the regrowth from being eaten e.g. by deer :smile:

Reply 3961

Syystole

That's the spirit mate

Original post by SachinNeedsHelp

Was planning then thought, whats.the ****ing point. Im not learning/understanding much **** now, what difference will learning at fkin 3am make. instead imma fuk off to bed and hope for the best tomorrow, otherwise ill be pulling the past papers and books out of my bin

Reply 3962

loperdoper

Original post by medactuary

How do you know if dominant epistasis is 13:3 or 12:3:1

You'll typically know from the context - if there are three potential outcomes of epistasis, it'll be 12:3:1, otherwise it's 13:3.

The difference between 12:3:1 and 13:3 is that when both genes are recessive, it produces the result normally seen by the first dominant gene. 13:3 is most common when the first gene being dominant blocks any protein (pigment etc) production, so then the double recessive offspring (aabb for instance) also blocks any protein production.

Reply 3963

ooxbridge

Original post by SachinNeedsHelp

well like someone else said, I've got nothing to lose but my uni place :wink:

Reply 3964

ooxbridge

Original post by hattieelena

any predictions please anyone? so desperate :frown:

copied and pasted from someone else x

1. Sex-linked or Epistasis cross with a Chi-Squared calculation2. Nitrogen Cycle3. Primate behaviour (Insight learning experiment?)4. Timber Management5. Succession6. Natural and Artificial Selectiongalapagos,something out of the topic about pcr/genome sequencing/insulin/rice etc, something out of the pages 232, 236-237 (muscles topic),brainshedding leaves (pg 223)how auxins stimulate shoot growth (pg 222)meiosisapoptosisepistasissomething out of the topic animal behaviors (social behavior in primates i think)Chi squaredNitrogen cycleAseptic techniques/Asepsis - that table on the bottom of pg 163Timber management

Reply 3965

ecwsky

Original post by corey7695

stressed?

just a tad :wink:

Reply 3966

ChoccyPhilly

Ugh, if we get a question on making an experiment that's worth 8 marks i may just commit suicide

Reply 3967

ecwsky

Original post by peanutcracker20

so can someone outline electrophoresis in bullet points and DNA sequencing

electropheresis is used to seperate DNA fragments based on their size
This is necessary for identification and analysis
1)DNA samples are treated with restriction enzymes
2)Then placed into wells at the cathode (negative part) end of the gel
3)The gel is immersed in buffer solution
4)As an electric current is passed through the solution DNA fragments move from the cathode--> anode (DNA is attracted to the anode because it is negatively charged)
5)shorter lengths of DNA move faster and further though the gel matrix, separating them out in order of length
Then often a dye is used to stain the fragments so they can be seen even more clearly.
Hope that helped!

(edited 8 years ago)

Reply 3968

ooxbridge

Original post by hattieelena

any predictions please anyone? so desperate :frown:

Reply 3969

George444

Guys, what do we need to know about abscission and senescence?

Reply 3970

Diamond Crafter

Must we need to know the experimental work done into the effects of gibberellins on stem elongation (pg.225 in the Heinemann txt bk.) in detail? Because I just can't get it into my head at the moment. :colonhash:

Reply 3971

Saltedcaramel1

Original post by George444

Guys, what do we need to know about abscission and senescence?

You just need to know that cytokinines inhibit leaf senscence, however drop in auxin causes drop in cytokinines and makes the abscisson zone more sensitve to ethene. drop in auxin means increase in ethene production and consequently more cellulase. cellulase digest the cell walls in the abscisson zone and eventually the petiole separates from le stem.

Reply 3972

Saltedcaramel1

Guys fire some questions at me, I would like to test my knowledge :smile:

Reply 3973

Shostakovish

Just farted :smile:

Also, in the Heinemanne book (page 195) it says how 'different species may release different amounts of energy per unit mass - hence, this method (pyramids of biomass) may not be accurate'
Could anyone explain what this sentence actually means?

Reply 3974

baymax96

Original post by peanutcracker20

same here and then i just keep finding more things i dont know about then have to stay up longer to do alll the work

I'm just risking not learning it

a night of sleep will probably benefit me more than trying to cram a whole syllabus which I'm not going to remember

resigned to the fact I'll get a U

Reply 3975

ChoccyPhilly

Original post by baymax96

I'm just risking not learning it

a night of sleep will probably benefit me more than trying to cram a whole syllabus which I'm not going to remember

resigned to the fact I'll get a U

This isn't maths where you need to be sharp to understand the questions, it's mostly fact recall. Even if you remember 30% of what you looked over in the extra hour before bed, that benefits you more than nothing imo