A2 Biology OCR June 2015 Revision Thread

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Thanks

You know in meiosis, the book shows four chromosomes for meiosis

But each human cell has 23 pairs of chromosomes, right? So in humans, how many chromosomes would be up for meisos? 46 pairs right? :hmmm:

Yes, prior to meiosis the 23 pairs replicate to produce 46 pairs.

How many cells would then be produced after meiosis is complete? 4, but with each cell with 23 chromosomes? Yes, 23 chromosomes (n).
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In a standard diploid (2n) body cell there are 46 chromosomes, that is, 23 homologous pairs (1 parental and 1 maternal).
Before meiosis, DNA replicates: 46 (2n) becomes 92 chromosomes (4n). In meiosis I, homologous pairs are separated to produce 2 daughter cells, each containing 46 chromosomes. Finally in meiosis 2 this halves again to produce 4 daughter cells, each with 23 chromosomes (n).

Does that make sense?

Reply 741

HeyThereHarry

Original post by AnnekaChan173

I'm more or less doing what you're doing, except I've made my notes and I'm doing practice questions as I go. Still need to finish my notes on Dopamine though. Do you wanna link that stretch and challenge notes thingy?

https://www.dropbox.com/s/c846q4mj16g26ek/f215%20stretch%20and%20challenge%20ideas.docx?dl=0

They seem to be based on the mark schemes to some of the stranger legacy/past spec questions. :smile:

Reply 742

AnnekaChan173

Original post by HeyThereHarry

https://www.dropbox.com/s/c846q4mj16g26ek/f215%20stretch%20and%20challenge%20ideas.docx?dl=0

They seem to be based on the mark schemes to some of the stranger legacy/past spec questions. :smile:

Thank you

Reply 743

Beni24

Hey guys, I'm retaking my F212 aswell as my F214 and F215 and there's so much content to remember! How is everyone revising for these exams? :smile:

Reply 744

Glh96

Does anyone have idea of the differences between a synapse and a neuromuscular junction?

There are the obvious ones (S= neurone and neurone, NMJ= neurone and muscle) but it is marked out in the specification and the textbook doesn't really have any comments on it?
I was wondering whether there were anymore, more specific ones that we should know?

Also when I have googled this question some of the answers have been contradictory to the textbook, such as saying that NMJ only use acetylcholine as a neurotransmitter whereas in the textbook it says that sympathetic neurones secrete the neurotransmitter noradrenaline between the neurone and the effector?

Thanks in advance!

Reply 745

Hilton184

Original post by Glh96

At the neuromuscular junction - in other words, the synapse between the postganglionic neurone and the effector, the neurotransmitter is acetylcholine.

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Reply 746

TheLegalDealer

Original post by Glh96

NMJ only has acetylcholine as the neurotransmitter while S has acetylcholine + many others

S is between 2 neurons while NMJ is between a neuron and muscle

S requires many action potentials to cause deporisation while the NMJ requires only one
+ S has many enzymes to breakdown the neurotransmitters

Reply 747

buxtonarmy

Original post by AnnekaChan173

Thank you

I don't suppose you know a website where I can access all of the legacy papers for F214 and F215? I think it's called central concepts or something??

Thank you :smile:

Reply 748

newrecord

Original post by buxtonarmy

I don't suppose you know a website where I can access all of the legacy papers for F214 and F215? I think it's called central concepts or something??

Thank you :smile:

Sorry to intrude- but they're on the OCR website! Just go to past papers and at the top it says Legacy Qualifications, you have to download the folders and the Central Concepts papers are in there :smile:

Reply 749

Munrot07

Original post by ums maestro

You know alleles, they are just mutations of the normal genes innit? :hmmm:

How do we know which is the normal gene and which is an allele? :hmmm:

Posted from TSR Mobile

In terms of a "normal" gene that is normally the dominant one (in a dominant-recessive interaction) as the recessive gene is a mutation resulting in a loss of function.

However, we use allele to just mean a version of a gene. So there is a gene that codes for eye colour and the versions of that gene are Brown (B) and blue (b). They are both alleles but in terms of the "normal" one, the B allele is the standard, unmutated allele.

Reply 750

tomixox

Original post by newrecord

What are these central concept papers?????

Reply 751

TheLegalDealer

Can someone explain grade boundaries to me , does it matter how far your into an A to get the ums mark ?? So does the ums make a difference so once your passed the threshold it doesn't matter if you got a high A or Low A n you'll get the same UMS mark

Thanks in advance

Reply 752

newrecord

Original post by tomixox

What are these central concept papers?????

They're basically the papers from the old course, but most of the topics are the same so you can use them as practice questions :smile:

Reply 753

Munrot07

Original post by TheLegalDealer

You get a raw mark, this is the exact mark you get on the paper. It is then converted into UMS according to how well everyone did. Every raw mark will have an associate UMS mark. It does matter how far you go into an A. You can get 80/100 UMS all the way up to 100/100 UMS if you have an A.

Reply 754

bakedbeans247

Original post by HeyThereHarry

https://www.dropbox.com/s/c846q4mj16g26ek/f215%20stretch%20and%20challenge%20ideas.docx?dl=0

They seem to be based on the mark schemes to some of the stranger legacy/past spec questions. :smile:

Hey at the end of that link there's a list of topics, are these what are expected to come up? :O Also who created that list a student/teacher?

Thanks for tht link btw.

(edited 8 years ago)

Reply 755

Boris Djouari

does anyone have any predictions for the f214 + f215 exams?

Reply 756

HeyThereHarry

Original post by bakedbeans247

Hey at the end of that link there's a list of topics, are these what are expected to come up? :O Also who created that list a student/teacher?

Thanks for tht link btw.

I just replied to you in the comments section but I'll do it here as well haha:

Yeah, but I don't think that's relevant for us because I don't think this document was created all that recently. I'm not sure who made it :smile:

Reply 757

HeyThereHarry

Original post by Boris Djouari

does anyone have any predictions for the f214 + f215 exams?

I'm unsure about f214, but i'm having strong feelings about galapagos islands and innate behaviour for f215

Reply 758

bakedbeans247

Original post by HeyThereHarry

Ahh no

haha i was pretty happy to find a predictions list as i've still got a lot to revise.

So what do you think will come up? :wink:

Reply 759

AnnekaChan173

Original post by Glh96

Does anyone have idea of the differences between a synapse and a neuromuscular junction?
Thanks in advance!

Original post by TheLegalDealer

I personally wouldn't state this. NMJ also has enzymes to break down neurotransmitters, in fact AChE is said to work rapidly at the NMJ. Does the book say anything about many APs being needed to cause depolarisation? I know it talks about many impulses leading to a larger output (summation). Makes sense, but I don't think it would be a marking point or an AVP. Naming some of the others may help also (dopamine, serotonin etcetc). At S, depolarisation leads to the transmission of another action potential, while at a NMJ, it leads to muscle contraction. You could talk about which membrane is depolarised too? Yeaaaaah, can't think of anything else really.

Original post by buxtonarmy

I don't suppose you know a website where I can access all of the legacy papers for F214 and F215? I think it's called central concepts or something??

Thank you :smile:

Good thing the other person replied, since I was wondering myself hahah! I'm using questions that I got from school, personally. Physics and Maths tutor has a load of questions too arranged in module packs, if that helps.