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JenLivYoung
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#1081
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#1081
Hello! As we get closer to the exam, I was wondering if people had done mocks at school or done their own version? We did the June 2012 paper as a mock, and my hand practically dropped off (you'd think I'd be used to it after English Lit, but nope). What kind of marks are people getting if so?
Very stressful times, 33 days to go!
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king101
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#1082
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#1082
(Original post by JenLivYoung)
Hey! We went through this today in class from our mock & this is the mark scheme we were given from last year. My teacher said that they check you have something from a range from this table, to check you have breadth and knowledge, if that makes sense? Ask if it doesn't, my brain is a bit of a mess at explaining today :')




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Hello,
Thanks for the reply! But I still DONT understand!
If I say only include 3 of those descriptor points, of under the same category, how do they actually mark the scientific content?

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erniiee
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#1083
(Original post by currydud)
can someone help me on this please.in the menstrual cycle, it says that low oestrogen levels inhibit the release of FSH and LH but after 10 days it says that high levels of oestrogen stimulate the release of FSH and LH. why does this happen? I asked my teacher and she said you don't need to know why but I would like to understand myself why, becasue it just makes no sense to me!
Basically, there is another hormone involved which actually stimulates FSH/LH production called gonadotrophin releasing hormone or GnRH (FSH and LH are gonadotrophins).

GnRH is released from the hypothalamus and stimulates the production of FSH or LH from the pituitary gland depending on whether its released in "fast pulses" or "slow pulses".

So, after the follicle is stimulated due to FSH production (from GnRH production) and oestrogen is released by it, oestrogen levels rise. Initially the rise in oestrogen has a negative feedback effect, by inhibiting GnRH release and so FSH production.

When the oestrogen reaches its peak of concentration or goes above a certain critical level, it then stimulates GnRH production (and in this case both slow and fast pulses result in the production of LH and FSH). The result is a positive feedback effect, whereby LH "surges", causing ovulation.

The exact mechanism of the switch from negative to positive feedback is apparently not well understood..but from what I have read, an increased level of responsiveness of the hypothalamus due to high oestrogen (and apparently progesterone levels) results in the positive feedback.

I just think of it as a threshold level, whereby once you hit the oestrogen threshold, GnRH is like "I'm free!!!" so LH (and FSH) rise too because it stimulates their production.

Hope that wasn't too deep! It all seems to be quite complex and there are a lot of factors contributing, so I think the textbook and teachers "dumb it down" so we stick to the key points.
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feelinginfinite
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#1084
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#1084
This may sound like an extremely vague question, but can someone please explain the entire order of section 16? Our class has been given "independent study" for this section and I'm struggling to understand if there even is an order (e.g is 16.1 - 16.3 an order? As in, cut DNA > in vivo + marking OR in vitro > gets you the DNA you want for reasons said in 16.5?) I'll write what I mean below:

1. DNA needs to be isolated = which can be done by restriction endonucleases or reverse transcriptase
2. This provides a section of DNA that you want which needs to be cloned = which can be done by the PCR (in vitro) or by using vectors (in vivo)

I'm so confused as to whether this entire section is a sequence of events or all separate techniques... If someone would prefer to PM me in detail I would be sooo grateful. Independent study is the worst

Edit: I have another question... What determines whether a restriction endonucleases will cut in a blunt way or a staggered way? From what I can see, it's completely dependent on whichever random RE it is... So we wouldn't be asked to identify which way it would be cut, would we?
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Gulzar
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#1085
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#1085
Does anyone have any ideas of any sites or material we can use for the "greater depth" part of the essay? I mean, can we just read something thats not on the spec but relevant to the essay title eg. if the title was about movement of ions we can talk about kidneys and excretion maybe? YOU NEED 2 OR MORE PARAGRAPHS OF EXTRA STUFF TO GET MAX MARKS!!!
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Gulzar
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#1086
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#1086
(Original post by JenLivYoung)
Hey! We went through this today in class from our mock & this is the mark scheme we were given from last year. My teacher said that they check you have something from a range from this table, to check you have breadth and knowledge, if that makes sense? Ask if it doesn't, my brain is a bit of a mess at explaining today :')




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But then does that mean if u have a topic from each of the 3 "big areas" you get all 3 Breadth marks? Or to get the 3 marks do u need every single topic in that mark scheme?
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Mocking_bird
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#1087
(Original post by Gulzar)
But then does that mean if u have a topic from each of the 3 "big areas" you get all 3 Breadth marks? Or to get the 3 marks do u need every single topic in that mark scheme?
For 3 marks in breadth you need one topic from each of the big topics.
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currydud
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#1088
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#1088
(Original post by erniiee)
Basically, there is another hormone involved which actually stimulates FSH/LH production called gonadotrophin releasing hormone or GnRH (FSH and LH are gonadotrophins).GnRH is released from the hypothalamus and stimulates the production of FSH or LH from the pituitary gland depending on whether its released in "fast pulses" or "slow pulses".So, after the follicle is stimulated due to FSH production (from GnRH production) and oestrogen is released by it, oestrogen levels rise. Initially the rise in oestrogen has a negative feedback effect, by inhibiting GnRH release and so FSH production. When the oestrogen reaches its peak of concentration or goes above a certain critical level, it then stimulates GnRH production (and in this case both slow and fast pulses result in the production of LH and FSH). The result is a positive feedback effect, whereby LH "surges", causing ovulation.The exact mechanism of the switch from negative to positive feedback is apparently not well understood..but from what I have read, an increased level of responsiveness of the hypothalamus due to high oestrogen (and apparently progesterone levels) results in the positive feedback. I just think of it as a threshold level, whereby once you hit the oestrogen threshold, GnRH is like "I'm free!!!" so LH (and FSH) rise too because it stimulates their production.Hope that wasn't too deep! It all seems to be quite complex and there are a lot of factors contributing, so I think the textbook and teachers "dumb it down" so we stick to the key points.
bloody hell, that's an excellent answer! thanks!
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Mocking_bird
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#1089
(Original post by feelinginfinite)
This may sound like an extremely vague question, but can someone please explain the entire order of section 16? Our class has been given "independent study" for this section and I'm struggling to understand if there even is an order (e.g is 16.1 - 16.3 an order? As in, cut DNA > in vivo + marking OR in vitro > gets you the DNA you want for reasons said in 16.5?) I'll write what I mean below:

1. DNA needs to be isolated = which can be done by restriction endonucleases or reverse transcriptase
2. This provides a section of DNA that you want which needs to be cloned = which can be done by the PCR (in vitro) or by using vectors (in vivo)

I'm so confused as to whether this entire section is a sequence of events or all separate techniques... If someone would prefer to PM me in detail I would be sooo grateful. Independent study is the worst

Edit: I have another question... What determines whether a restriction endonucleases will cut in a blunt way or a staggered way? From what I can see, it's completely dependent on whichever random RE it is... So we wouldn't be asked to identify which way it would be cut, would we?
You've pretty much just got the idea there. You cut the section of DNA using restriction endonuclease or reverse transcriptase and then you can amplify the sample with PCR or vectors.

& Yes, its just dependent on the type of restriction enzyme so I highly doubt they can ask us how it would cut.
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feelinginfinite
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#1090
(Original post by Mocking_bird)
You've pretty much just got the idea there. You cut the section of DNA using restriction endonuclease or reverse transcriptase and then you can amplify the sample with PCR or vectors.

& Yes, its just dependent on the type of restriction enzyme so I highly doubt they can ask us how it would cut.
You've made my day by replying considering it's taken me all day to get my head around the first 4 parts of section 16 Thank you! +1
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MLogan
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#1091
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#1091
(Original post by erniiee)
Basically, there is another hormone involved which actually stimulates FSH/LH production called gonadotrophin releasing hormone or GnRH (FSH and LH are gonadotrophins).

GnRH is released from the hypothalamus and stimulates the production of FSH or LH from the pituitary gland depending on whether its released in "fast pulses" or "slow pulses".

So, after the follicle is stimulated due to FSH production (from GnRH production) and oestrogen is released by it, oestrogen levels rise. Initially the rise in oestrogen has a negative feedback effect, by inhibiting GnRH release and so FSH production.

When the oestrogen reaches its peak of concentration or goes above a certain critical level, it then stimulates GnRH production (and in this case both slow and fast pulses result in the production of LH and FSH). The result is a positive feedback effect, whereby LH "surges", causing ovulation.

The exact mechanism of the switch from negative to positive feedback is apparently not well understood..but from what I have read, an increased level of responsiveness of the hypothalamus due to high oestrogen (and apparently progesterone levels) results in the positive feedback.

I just think of it as a threshold level, whereby once you hit the oestrogen threshold, GnRH is like "I'm free!!!" so LH (and FSH) rise too because it stimulates their production.

Hope that wasn't too deep! It all seems to be quite complex and there are a lot of factors contributing, so I think the textbook and teachers "dumb it down" so we stick to the key points.
:adore:
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erniiee
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#1092
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#1092
(Original post by feelinginfinite)
This may sound like an extremely vague question, but can someone please explain the entire order of section 16? Our class has been given "independent study" for this section and I'm struggling to understand if there even is an order (e.g is 16.1 - 16.3 an order? As in, cut DNA > in vivo + marking OR in vitro > gets you the DNA you want for reasons said in 16.5?) I'll write what I mean below:

1. DNA needs to be isolated = which can be done by restriction endonucleases or reverse transcriptase
2. This provides a section of DNA that you want which needs to be cloned = which can be done by the PCR (in vitro) or by using vectors (in vivo)

I'm so confused as to whether this entire section is a sequence of events or all separate techniques... If someone would prefer to PM me in detail I would be sooo grateful. Independent study is the worst

Edit: I have another question... What determines whether a restriction endonucleases will cut in a blunt way or a staggered way? From what I can see, it's completely dependent on whichever random RE it is... So we wouldn't be asked to identify which way it would be cut, would we?
16 is so big :eek: that was mean of them to make you learn it in your own time.

I'd say the book is in order for 16.1-16.3. Those sections explore each of isolation, insertion, transformation, identification and growth/cloning. 16.4 touches on applications of this..and 16.5-16.8 apply what you've covered in 16.1-16.3/4 in specific contexts.

Definitely have a look at the specification so you know you've got all bases covered!

(Original post by currydud)
bloody hell, that's an excellent answer! thanks!
No problem!

(Original post by MLogan)
:adore:
:lol:
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erniiee
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#1093
Breaking relevant news:

Embryonic stem cells: Advance in medical human cloning

Human cloning has been used to produce early embryos, marking a "significant step" for medicine, say US scientists.
The cloned embryos were used as a source of stem cells, which can make new heart muscle, bone, brain tissue or any other type of cell in the body.
The study, published in the journal Cell, used methods like those that produced Dolly the sheep in the UK.
However, researchers say other sources of stem cells may be easier, cheaper and less controversial.
Opponents say it is unethical to experiment on human embryos and have called for a ban.
Stem cells are one of the great hopes for medicine. Being able to create new tissue might be able to heal the damage caused by a heart attack or repair a severed spinal cord.
There are already trials taking place using stem cells taken from donated embryos to restore people's sight.
However, these donated cells do not match the patient so they would be rejected by the body. Cloning bypasses this problem.
The technique used - somatic cell nuclear transfer - has been well-known since Dolly the sheep became the first mammal to be cloned, in 1996.


Rest of the article here:
http://www.bbc.co.uk/news/health-22540374

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AtomicMan
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#1094
(Original post by erniiee)
Breaking relevant news:



Rest of the article here: [/FONT][/COLOR]http://www.bbc.co.uk/news/health-22540374

[/FONT][/COLOR]
Thought I could stop stalking bbc health after interviews :lol: Going to have to sub to new scientist again to get some ideas for the essay. Have you been revising earlier units?

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cheesypuff
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#1095
the alevel bio course is filled with stuff your not meant to know at this level.

I mean how to transfer genes....really
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erniiee
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#1096
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#1096
(Original post by AtomicMan)
Thought I could stop stalking bbc health after interviews :lol: Going to have to sub to new scientist again to get some ideas for the essay. Have you been revising earlier units?

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Aha, I did :lol: I just heard it on ITV news so sought after an article and voila bbc news had that on their website as a top story!

Ah is it any good?

Only very briefly, tbh I'm gonna focus on knowing Unit 5 and and note any synoptic links from within the unit rather than go over Units 1, 2 & 4. Have you?
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Tikara
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#1097
When do you get double stranded RNA? like the ones that are cut up into siRNA
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Mocking_bird
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#1098
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#1098
(Original post by Tikara)
When do you get double stranded RNA? like the ones that are cut up into siRNA
Not sure which answer your looking for so i'll go for both :P

You only get it when its needed to be cut up to make siRNA (and in some viruses but we dont need to know about that), because they need complimentary strands for one to bind to the enzyme.

The reason RNA usually isn't double stranded:
"The chemical inertness that double-strandedness grants to DNA would be a hindrance in the case of RNA, which relies on its ability to fold and contort somewhat (a little like a protein) to accomplish some of its tasks."
http://medicguide.blogspot.co.uk/200...d-but-rna.html

^ worth a read even if this wasnt what your question was aiming at :lol:

or...

You get it during regulation of translation as it causes mRNA to be broken down after transcription so translation cannot occur.
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DoeADeer
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#1099
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#1099
Hi, I don't really understand positive and negative feedback in relation to the oestrous cycle. Could someone explain it to me please?
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Rebeelouise
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#1100
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#1100
Got a B on the mock I did in class the other day 5 marks off an A! Which makes me really pleased considering I have over a month to ace it! Yay!


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