Edexcel A2 Biology Unit 4(6BIO4) 13/06/11 - OFFICIAL THREAD !

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Reply 480

imaam

Can someone list the main points of gel electrophoresis please...

Reply 481

shanshine

Original post by imaam

Can someone list the main points of gel electrophoresis please...

DNA fragments amplified in PCR
then placed in an AGROSE GEL MEDIUM
with a buffer solution to keep ph constant
The Gel contains a dye that floreces under uv light
DNA is places at the negitive end and current is passed through
because the phosphate group in dna has a negitive charge, the dna moves to the positive end
depending on the size and charge the fragments move at differnt rates
this causes them to spread and can be veiwed as bands.
it can then be placed under uv light for analysis

Alternitivly to uv light southen blotting can be used to anylaise the dna
in southen blotting an ALKALINE buffer is added, this denatures the dna so the strands seperate and the bases are exposed
a nylon filter is placed over the dna and dry absorbant paper draws the dna solution from the gel to the filter leaving it as blots on filter

hope that helped

Reply 482

imaam

Original post by shanshine

Definitely helped thanks!!

Reply 483

Mkal18

i didnt like the paper AT ALL =/

Reply 484

Lexi Templeton

Original post by Mkal18

i didnt like the paper AT ALL =/

Which questions did u face the most problems? :/

Reply 485

LadySmythe

Discussion of edexcel exams is not permitted until midnight for morning exams and 4.30am for afternoon exams. Please read the announcement for more details

Reply 486

bashx

How did everyone find this?
I thought it was a little difficult especially the timing!!! There was too many long mark answer questions and so much of it

Reply 487

Godot123

You are not allowed to talk about it.

EDIT: As far as I am aware.

(edited 12 years ago)

Reply 488

aps18

I found this exam terrible.

I totally agree with the timings, but also a couple of questions seemed odd for the content we learnt.

"viruses are treated with antibiotics - explain how antibiotics treat viruses" was this a trick question ???

x

Reply 489

rjblack22

I did not like it at all. And that virus question was nasty of them! Their books go on and on about how antibiotics CANNOT help viruses then they ask the exact opposite.

My dad says it's probably to do with antibiotics helping with any secondary infections, as you become more susceptible to secondary infections if you already have a virus. I did not get that at all in the exam! :-S Sick of edexcel and their ridiculous questions, ask us about content for goodness sake! All the complex stuff we spend hours learning they give like 1 mark quesitions about. Argh, I really didn't like that paper.

:-(

Reply 490

KearaLee

I actually liked it, luckily i've had to resit all four which helped me know the answers to the Mitosis question and the plants. Glad i went over it all. I just thought the seaweed question was awful.

Reply 491

tophothari

international exams finished, therefore we can talk about it now as its close to midnight.

i had few problems with the paper.

1) what did you put for the levels of shore for red and green seaweed?

i put middle for red. assume top shore level is dry and not shallow water. middle is shallow water and lower shore is deepwater. if its emitting red color then red must have reached it, but red cannot penetrate deepwater therefore red seaweed must be in middle shore.

I put all for green seaweed, as green penetrate deep water, and its reflecting green light so green light must have reached it.
The data suggests that red seaweed absorbs green the most and green seaweed absorbs red the most >< which kinda confused me!!!

2) for virus, using antibiotics as part of the treatment, i put;

- antibiotics only work on bacteria and not virus
- some bacterial diseases have similar symptoms as influenza
- some antibiotic used to check if the infection is viral or bacteria.
- if symptoms are gone then infection is bacterial and if symtoms persist then its viral.

3) how the hell do you measure species density? is it same as % cover? if so then i did get it right, i described line transect along the slope.

Reply 492

Pwiii

Original post by aps18

About that question, I wrote it was a artificial passive immune response to help the immune system kill the infection off but is only short term and no memory cells of antigen receptors produced ...
Does that sound right to you??

& about the seaweed question
I said the schlywa thing was in middle of shore because of more green wavelength indicating more photosynthesis being made and ulva lactuca something was at lower down the shore because of higher blue wavelengths because of reflection of the sea on the seaweed.
Does that sound right?

Reply 493

tophothari

Guys what did you think of the paper? I think the time wasn't enough as it had lots of long questions, however i managed to finish it.

The seaweed question confused the hell out of me, but i did in a weird logical way.

Can you guys remember any questions and what answers you put for them?
Please do share, thanks :smile:

Questions I can remember:
1) how does DNA analysis provide evidence that humans and apes are closely related.

2) why sometimes you use antibiotics as PART of the treatment for viral infections?

3) Describe how you would do a transect to measure the species density across teh slope.

4) Why some scientists argue that reduction in the use of fossil fuel will not do any good in handling global warming (6 marks) ( i put a lot of BS in this one :frown:

)

5) How does CO2 and methane maintains global average temperature

6) How does gel electrophoresis work? (loved this question :biggrin:

)

7) give ABIOTIC factors that affect rate of rigor mortis (i was like wtf, but i put temperature and environment condition (like land or sea of where body is))

8) what factor affects rate of rigor mortis immediately after death ( i put oxygen in atmosphere :/ )

Please share your memories and what you wrote for them questions ! thanks :smile:

Reply 494

tophothari

Legal official thread is here http://www.thestudentroom.co.uk/showthread.php?t=1676443 . This one was created before midnight, so its most likely to get closed.

Reply 495

Pwiii

I don't remember a measure the species diversity question... how many marks and where was it on the paper?? :s-smilie:

Reply 496

Godot123

How many marks was question 3 you wrote there?

Reply 497

Rothers

Whaaaa I don't remember seeing q3 at all!! Worried now... and I thought it was meant to be 4.30am before you can talk about Edexcel exams?

Reply 498

Godot123

Yh, I didnt notice Q3 either.

The mods arent patrolling atm I guess.

Reply 499

Zabukar

Q3 ?? Really . They might as well of given us any questions NOT to do with biology as the whole paper seemed like it. Tested no knowledge of good A2 biology and if so for 1/2 mark questions. Exam sucked, nothing on Protein synthesis :/ ??
I found the exam ok, based on what was given. But Edexcel could of done soo much better as in topics they should of tested.