A2 Biology OCR June 2015 Revision Thread

Does anyone know what siRNA is and if we have to know about in the exam? I saw a couple of questions on it but can't find them anymore.
Thank you

Yes- its a good idea. Just done a past paper where you got marks for mentioning the names of animals. It would be good to learn specific examples for innate and learned behaviour too

Yeah. Do we need to know examples for interspcfifc competition intra and predator prey relationships? So for predator prey you've for lynx predator and snowshoe then you've got the grey and (other coloured ) rabbits for inter what about intra eg??

Where in the text book is the chain termination method?

Yes, the spec says you need to know examples, and it's come up before.

For interspecific, I would personally advise using the mink/water vole or red/grey squirrel comparisons, as they're specific species you can name.

Intraspecific competition happens within all species, so you can basically name any species you like provided you can apply it - for instance, you could talk about plants competiting for nutrients of the soil, as well as light and water, or you could use the example of lions defending territory and hunting for their own pack against outsiders of the group.

What example could you give for habituation? And taxes ?

Describe how artifical selection can be used to produce bread wheat,Triticum Aestivum.
I understand the diary cow bit but the stuff on the other two looks complicated.

For taxes, I only know the one given in the textbook. Taxes is where woodlice will start moving when taken out of a dark/damp area, and they will keep moving until they reach the dark/damp area.

Habituation: rabbits by a busy roadside learn to not run away from cars as they drive past, although they will still run away from other stimuli

(bread wheat is triticum aestivum, so it's only asking for one other thing)
Artificial selection is selecting wheat in order to give it a higher yield. It's selected to have a larger yield, all of similar heights to make harvesting easier. Artificial selection is just the simple "pick the best, breed, pick those best, breed"

Nah, the woodlouse one is kinesis. It is non-directional. When woodlouse in unfavourable condition, it increases rate of random movement

Taxis is the directional one. For example, if you shine a torch at an animal, it runs away from the light source

You can also do something like birds learning to ignore scarecrows for habituation one

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Do we need to about polyploidy, the different species and their genomes?

Also, when does independent assortment of chromosomes occur in meiosis? My textbook says Metaphase 1 and 2, but I don't see how that's correct if cytokinesis and nuclear envelope formation doesn't occur until telophase? How can the chromosome be 'sorted' into separate cells, if they haven't even begun to be pulled apart yet?
Cheers

Independent assortment of chromosomes = metaphase 1

Independent assortment of chromatids = metaphase 2

They're randomly arranged at the equator, just before being pulled to opposite poles by the spindle fibres

How they line up at the equator determines which cell they go into innit
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I would check the spec and see what they've said, but the end of f215 papers often is a series of questions where you make comparisons between two things - so I wouldn't be surprised if "what's the difference between DNA and (t/m)RNA" came up or similar.

It wouldn't be a bad idea to be aware of the structure of tRNA/mRNA, at least.

Guys I've got a high B in f211, and D's in both of my coursework, Im retaking f212,f214 and f215. If i get a B in f212 and f214 and maybe a high C in f215, Would that be a B overall?

Is it even worth asking for predictions after f214?