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A2 Biology OCR June 2015 Revision Thread

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Only the basement membrane as it has a fine mesh of collagen fibres that don't allow large molecules e.g. proteins through . The fenestrations (holes) in the capillary wall allow all solutes to pass through except proteins

Thank you😊

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Reply 1001

LaurenCocking

Hi, I don't know whether it's already been asked, but has anyone found the June 2014 F214 and F215 papers? I've run out of past papers to do!

Reply 1002

RagaZ

Original post by LaurenCocking

Hi, I don't know whether it's already been asked, but has anyone found the June 2014 F214 and F215 papers? I've run out of past papers to do!

http://www.thebiotutor.com/past-papers3.html

Reply 1003

loperdoper

Original post by LaurenCocking

Hi, I don't know whether it's already been asked, but has anyone found the June 2014 F214 and F215 papers? I've run out of past papers to do!

Have you tried doing some of the legacy papers? They're available on the OCR website and whilst they're structured a little differently and include things you don't need to know, they do still have some good questions for practice on there (although marking is tricky because it assumes you know things that aren't on the current spec)

Reply 1004

goonieskellie

Hey guys, just wondering what roughly the grade boundaries are for A*s on the past papers? both F214 and F215? I know they don't mark it like that, but just wondering as a rough guide (:

Reply 1005

medactuary

What does it mean to say an ecosystem is dynamic ?

Reply 1006

maisie__x

Original post by medactuary

What does it mean to say an ecosystem is dynamic ?

A complex ecosystem that is continually changing in terms of community members and physical factors. That's the definition I've learned but if anyone else has something to add please let me know! :smile:

Reply 1007

melissadawson

Can someone explain to me anaerobic respiration in yeast?

Reply 1008

ChoccyPhilly

Original post by melissadawson

Can someone explain to me anaerobic respiration in yeast?

Undergoes glycolysis as usual to get pyruvate.

Pyruvate decarboxylase turns pyruvate into ethanal and releases a carbon dioxide molecule
Ethanal is reduced by NADH via enzyme ethanol dehydrogenase to produce ethanol.

(edited 8 years ago)

Reply 1009

Hilton184

ImageUploadedByStudent Room1433088777.973767.jpg

ImageUploadedByStudent Room1433088798.402515.jpg

Is my answer worthy of the marks? I don't understand why they use the notation they have. Surely the notation I have used is the most appropriate?

This is F215 June 10 question 2bii

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Reply 1010

maisie__x

Original post by Hilton184

I'm pretty sure you get all the marks there :smile:

Reply 1011

ChoccyPhilly

Good luck to any unfortunate unit 2 resitters tomorrow! i share your pain

Reply 1012

ParzivaI

Hi, can anyone explain to me the sequencing of a genome? thanks in advance

Reply 1013

TheLegalDealer

simple Q guys , what is meant by substrate-level phosphorylation ?

Reply 1014

Hilton184

Original post by TheLegalDealer

simple Q guys , what is meant by substrate-level phosphorylation ?

Production of ATP by transfer of a phosphate group to ADP without the use of ATP synthase membrane protein - ie ATP not made by making use of proton motive force.

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Reply 1015

Hilton184

Original post by maisie__x

I'm pretty sure you get all the marks there :smile:

Okay great :smile:

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Reply 1016

TheLegalDealer

Original post by Hilton184

Production of ATP by transfer of a phosphate group to ADP without the use of ATP synthase membrane protein - ie ATP not made by making use of proton motive force.

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Thank you ! and what is the evidence for chemiosmosis ?

Reply 1017

CamilleClarke

Could someone explain to me what ganglions are and therefore what pre and post ganglionic neurones are? ( in relation to parasympathetic and sympathetic subsystems) thanks!

Reply 1018

Hilton184

Original post by TheLegalDealer

Thank you ! and what is the evidence for chemiosmosis ?

Spec says we only have to 'evaluate' evidence for chemiosmosis so I don't think we have to recall it, I wouldn't bother learning it.

But something along the lines of...

pH of inter membrane space much lower than pH of matrix.
Disrupting ATP synthase enzyme prevents production of ATP, but electron transport chain still occurs.

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Reply 1019

medactuary

Original post by ParzivaI

Hi, can anyone explain to me the sequencing of a genome? thanks in advance

- genomic DNA mapped using a micro satellite
- DNA broken down into sections of 100,000 base pairs
- Place each section into separate BACs and place the BACs into E.coli (by transformation). They will divide and form clone libraries. Each colony will contain copies of the same section of DNA.
- DNA extracted from E.coli and restriction enzymes cut them up into smaller fragments. We have more than one piece of the same section so we get overlapping fragments if we use different restriction enzymes as they cut the sections at different places.
- Electrophoresis - fragments separated according to size can anyone confirm that electrophoresis occurs here and not after fluorescent-chain terminating nucleotides are added?
- Sequence DNA by adding free nucleotides. When a fluorescent chain-terminating nucleotides is added no more nucleotides are added. This will happen repeatedly with each 'overlapping fragment' and the idea is if you do it enough times every base should have been 'hit' by a fluorescent-chain terminating nucleotide so you can work out what each base is in your section of DNA.
- Computer compares overlapping regions to assemble the DNA sequence of the section you placed into the BAC.
- Overlapping sections of DNA mapped to place all of these BAC sections in the correct order.
- Each DNA section is sub-cloned into plasmids as automated sequencing of small section of DNA in plasmids carried out