F215 - Revision thread 13th June 2011

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Original post by thecookiem0nster

The ocr book really makes it confusing. I was confused too

Gibberellins cause stem elongation.

Heres the evidence:

In the same species, some plants are dwarfs and others are tall plants. It was found that tall plants had more gibberellins than dwarfs. A mutant plant without the gene for creating gibberellin did not grow tall. But when one of it’s branches were grafted onto a normal plant, the graft grew tall. Therefore, gibberellins are responsible for stem elongation

i know the black OCR book confuses everything! thanks though that makes sense i will have another read :smile:

Reply 2161

intellectual1

Original post by SR198198

DUDES AND DUDETTES, thank me later, If anyones looking for questions i got a ****load, check it: so my mate emailed this college asking if he could use this software to take only questions that are relevant to the new syllabus from old exam papers, and they let him so he made a dope file of compilations of questions for each of the 4 modules split up into sections.

this is the download link:

https://docs.google.com/leaf?id=0B0PrtPSCteJZZmUzN2YwMjUtOWE3OS00Y2VhLTlhYTMtY2M0MDVjYWVmYTI0&hl=en

Go to the Question bank folder, then the Unit 5 folder.
Maadness.

There's no folders...just says Resources.zip quite a large 200MB file hmmm so that has all the past papers? :biggrin:

Reply 2162

katie93

Original post by DrDr

DNA to RNA I think you mean?

nope, reverse transcriptase does the reverse
you have the mRNA, add reverse transcriptase and it produces the complementary single stranded DNA molecule (cDNA)

Reply 2163

SR198198

Original post by intellectual1

There's no folders...just says Resources.zip quite a large 200MB file hmmm so that has all the past papers? :biggrin:

the folders are in the zip file man.

Reply 2164

DrDr

Original post by rebeccalouise_92

how does greater environmental resistance cause a population to shrink? thought it would grow...

Env. resistance essentially means that pressure is being put on species, essentially weeding out those not with an advantageous phenotype for the stress being put on them.

Eg volcano spews out over surrounding areas and white moths die out because they no longer have an advantage with their phenotype, whilst black moths which were the minority before can start to become more prominent.

Reply 2165

praj1

hi could someone explain to me Gene Linkage....
i am so stuck on that atm!

Reply 2166

Jhyzone

Original post by DrDr

DNA to RNA I think you mean?

No, you're right its RNA to cDNA.
:biggrin:

Reply 2167

786girl

someone ask me a question on anything!!!!

Reply 2168

gemmurdoch

Original post by DrDr

DNA to RNA I think you mean?

the whole point of reverse transcriptase is that you work backwards from the formation of mRNA to retrieve the sequence of DNA bases so you can sequence the DNA to form more copies. You don't have the DNA to form the mRNA to begin with so this is impossible.

Reply 2169

katie93

Original post by rebeccalouise_92

how does greater environmental resistance cause a population to shrink? thought it would grow...

initially surely the increase in selection pressures would cause only a few individuals to survive. like imagine if suddenly the temperature of the earth increased, only a few individuals would have the correct combination of alleles to allow them to survive in such an environment - so population shrinks.
over time it would regrow though

Reply 2170

gemmurdoch

Original post by 786girl

someone ask me a question on anything!!!!

what are the advantages and disadvantages of somatic gene therapy?

Reply 2171

DrDr

Original post by katie93

nope, reverse transcriptase does the reverse
you have the mRNA, add reverse transcriptase and it produces the complementary single stranded DNA molecule (cDNA)

I know that reverse transcriptase does mRNA to cDNA, but someone in the thread (think it was cookiem0nster?) also said it did DNA to RNA.

It certainly doesn't do mRNA to DNA, but does do mRNA to cDNA :P

Reply 2172

Killmepls

Original post by 786girl

someone ask me a question on anything!!!!

What is the meaning of life?

Also what do the five plant hormones do? e.g auxins gibberelins

Reply 2173

katie93

Original post by 786girl

someone ask me a question on anything!!!!

outline the 2 ways of sequencing a genome
(automated - using PCR, and using BACs)

Reply 2174

Jhyzone

Original post by rebeccalouise_92

how does greater environmental resistance cause a population to shrink? thought it would grow...

It can shrink due to biotic(living organisms) and abiotic(non-living of the environment) factors :biggrin:

If environmental resistance is great eg competition (biotic factor) it can cause a population to shrink because it means that predators will be in greater numbers and the prey will be in low numbers.

But then population can stabilise again since if all the prey were gone, predator population will decrease and so prey population will increase again. :smile:

Reply 2175

-Jaz-

Original post by subsist

Hey guys important question here. It says that the hypothalamus controls the fight and flight response including increase in heart rate but isnt it the medulla oblongata that controls the heart rate? Also, how does the medulla oblongata control the action of the gut wall and what the heck is it used for? Thumbs up for answers. cheers x