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A2 Biology OCR June 2015 Revision Thread

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Original post by shalalondon
Difference between locus and linkage please? Anybody??


Locus - the location of a gene on its chromosome

Sex linkage (I presume) is all about genes on the sex chromosomes - X and Y. The main things to remember are the case studies of haemophilia and colour blindness, and how men are far more likely to get them than women, since the only copy of the associated genes exists on the X chromosome. For example, haemophilia is caused by a recessive allele, but since there's nothing on the Y chromosome, it will always be expressed.
(edited 8 years ago)
What do we need to know about Galapagos island?
OCR biology past papers are just about the most irrelevant things to use to revise

There is no continuity between papers and they change the paper a lot between exam seasons

If you do them, do them to familiarise yourself with dodgy OCR wording but don't use them as your sole source of last minute revision
Original post by Saltedcaramel1
Yaaas, it's pretty simple and it hasn't come up in forever so pretty good chance it will tomorrow :smile:


Came up in jan 2013


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can anyone explain to me the 2 ways of defining a species ?
Anyone made predictions on here or not?
Biological species concept - group of organisms of the same species that can interbreed with one another and produce a fertile offspring
Phylogenetic species concept - group of organisms that are sharing the same morphology, physiology and occupy the same niche
Original post by TheLegalDealer
can anyone explain to me the 2 ways of defining a species ?
(edited 8 years ago)
Original post by MiniSlash
Correct me if I'm wrong, this is a summary of the main roles of these hormones (off the top of my head)

Plant Hormones:
Auxin
- Apical dominance

Gibberellin
- Cell elongation

Abscissic acid
- Stimulates the production of 'ethene'

Ethene
- Fruit ripening and leaf abscission

Auxins are used in rooting powder
Auxins can be used as weedkillers

I know of some kind of abscissic acid (unanamed in my revision guide) that is an anti-transiprant; stops transpiration by closing Stomata

If you chop off the tip of a plant lateral/axillary buds grow, since there's no more apical dominance.

Regarding tropisms...

Phototropism = light
Geotropism = gravity
Thigmotropism = touch

Positive tropism = toward stimulus
Negative tropism = away from stimulus

Phototropism
Auxins accumulates on the shaded side of the plant, these cells take up more water and elongate lengthways - they are somehow structured so that they don't widen, but lengthen.

I hope this helps


thank you very much this is great :biggrin:
Original post by Student23478
Has anyone got a link to the old past papers??


how old
Original post by TheLegalDealer
can anyone explain to me the 2 ways of defining a species ?


There's the biological species concept which states that a species are a group of organisms that are able to reproduce fertile offspring.

The problems with the biological species concept is that it can be hard to see what species a newly discovered organism belongs to because their reproductive behaviour may be unable to be measured. For instance, if the organism reproduces asexually, species is now extinct, ethical/practical issues.

So most scientists use the phylogenetic concept which looks at the history of an organism. Looking at what it is related to and how closely.
http://us22.chatzy.com/94903706046868 join us on this chat if you want to do some revision and help each other :smile:
Original post by peanutcracker20
thank you very much this is great :biggrin:


Don't mention it! Explaining it to others helps me with my own revision, so it's a win win.
What are the predictions for this years paper?
Why are there so many questions asking about how you'd carry out an experiment? IS this a proper thing as my teacher said absolutely nothing about this
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tewas
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Anybody have any questions they want answered?
Original post by tewas
Anybody have any questions they want answered?


Do you understand all that shiz about monopyletic, paraphyletic, haplotypes, clades, taxa and all that shiz :sigh::mad:

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I need to destroy this paper for my A but I dont think its gonna happen. :frown:
How much genetics stuff will come up? :smile:
Original post by BioAgent
I need to destroy this paper for my A but I dont think its gonna happen. :frown:


YES YOU CAN!! JUST DO IT!!!

https://www.youtube.com/watch?v=nuHfVn_cfHU
Original post by BioAgent
I need to destroy this paper for my A but I dont think its gonna happen. :frown:


Dont worry bro. Everyone will fail cos we all have a shiz load of exams this week and stuff

Boundaries gonna drop like to 60 for an A

It's possible brah. It's possible :yes:

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