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OCR Biology F215 Control, Genomes and Environment Fri 15 June 2012

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In my textbook it states that the Rhizobium provide the legumes with fixed nitrogen - it doesn't say which types. I never knew it wasn't nitrates. Where did you get that information from?

Nitrogen reductase in Rhizobium reduces nitrogen gas (contained in air in soil) to ammonium ions

Reply 781

Fizzo

Has anyone else done any past papers yet? I've done the specimen, Jan 2010, June 2010, jan 2011... But I only get around 60%! I know the grade boundaries are lower than in other subjects but it's still only a B and i need an A*.

Anyway, I often feel I know the stuff quite well but the exam questions ask about things not directly related to the syllabus and they're also often ambiguous... Does anyone have any hints/tips on exam technique to ensure you answer in the way the mark schemes want?

Reply 782

splendidsun

Original post by Princess Kawaii

describe the role of the brain and nervous system in the co-ordination of muscular movement

The cerebellum contains over half of all of the nerve cells in the brain. These neurones carry impulses to the motor areas in the cerebral cortex so that motor output can be adjusted according to particular requirements (for e.g. operation of antagonistic muscles to coordinate contraction or relaxation/ judging position of objects and limbs). It plays a key role in coordination of movement and posture, and part of this role is processing sensory information from several locations such as the retina, balance organs in ear, the joints..

(edited 11 years ago)

Reply 783

Fizzo

Does anyone else find exam questions are often ambiguous/not directly related to the syllabus?

I feel I know the content quite well but struggle with vague questions and strict mark schemes... Any hints/tips on how to make sure you answer the questions in the way the mark schemes want?

Reply 784

rasklatz

Original post by Fizzo

I am in exactly the same position couldn't have phrased it bettwe myself :colondollar:

Reply 785

racheatworld

Original post by Sparkzz

Well Rhizobium bacteria converts nitrogen gas to ammonium ions. The enzyme present in the bacteria (nitrogen reductase) does this reaction in anaerobic conditions. There are nitrifying bacteria in the soil, eg Nitrosomonas bacteria which can then convert the ammonium ions to nitrite ions, and these nitrite ions can be converted to nitrate ions by Nitrobacter bacteria. Rhizobium will only convert nitrogen gas to ammonium ions.

Thanks! My textbook is far too vague.

(edited 11 years ago)

Reply 786

racheatworld

Original post by TourettesUnicorn

O lord that's a long one.

Gene therapy is basically swapping a faulty gene for the properly functioning one.
There are two ways to do it: Somatic Cell gene therapy and Germline gene therapy.

Be careful, it isn't swapping of a faulty gene for a functioning one. For gene therapy (eg somatic), the functioning gene is inserted into cells which are affected by the disease, but the faulty gene is not replaced. The faulty gene remains in the cell, it is just that the functioning gene now causes the correct polypeptide to be synthesised which means that the faulty gene is no longer an issue, even though it is still there.

Reply 787

TourettesUnicorn

Original post by racheatworld

thanks, I'll be sure to remember that :smile:

I'll go back and correct the post

Reply 788

racheatworld

Original post by TourettesUnicorn

thanks, I'll be sure to remember that :smile:

I'll go back and correct the post

No problem :biggrin:

I always find I remember stuff far more when I've made a mistake or have lost a mark in a question, it helps :smile:

Reply 789

TourettesUnicorn

Original post by racheatworld

No problem :biggrin:

I always find I remember stuff far more when I've made a mistake or have lost a mark in a question, it helps :smile:

Yeh I know what you mean, I might actually be able to remember how it works now :smile:

Reply 790

Lalaa

Original post by walkbesideme

A random sample of 1000 people was taken and it was found that 20 people were carriers of cystic fibrosis.
given that only one of these 20 shows symptoms of the condition, use the hardy weinberg principle to calculate the following (answers should be given to 3sf where appropriate):

a) The percentage of the population who are not affected or carriers (1)
b) The frequency of the recessive allele (1)
c) the frequency of the dominant allele (2)
d) Outline what asumptions have been made about this sample (3)

(7 marks)

Hey whats the answers for this?

Reply 791

walkbesideme

Original post by Lalaa

Hey whats the answers for this?

Hi - sorry i made the question up late last night and looking back the numbers don't work but here have another to attempt =)

Huntingtons is a disease caused by a dominant allele. In a random sample of 2000 people from a population - which can be assumed to be representative of the entire population of humans - 195 people were found to have the condition.

Given this information calculate the following using the Hardy Weinberg principle where appropriate:

a) The percentage of the population affected by this condition. (1)
b) The frequency of the recessive allele, q. (2)
c) the frequency of the dominant allele , p. (1)
d) the number of heterozygotes in this random sample. (1)
e) state any assumptions which were made during these calculations. (2)

Reply 792

Sparkzz

Original post by walkbesideme

I'll give a go. If its incorrect let others have a try then reveal answers later. Or if possible pm me :smile:

a) 9.75%
b) 95%
c) 5%
d) 190
e) random mating, large popn, no mutation, no migration, no genetic drift, no selective advantage

This was posted from The Student Room's iPhone/iPad Ap

Reply 793

skylight17

Original post by Fizzo

Anyway, I often feel I know the stuff quite well but the exam questions ask about things not directly related to the syllabus and they're also often ambiguous

I have this exact same problem, but it is the same for everyone else.

This is why the grade boundaries are so low!

Done all the past papers

June 10 (58)
Jan 11 (60 - this was exactly the A!)
June 11 (65)
Jan 12 (68)

Reply 794

Fizzo

Original post by skylight17

Looks like you're pretty much in exactly the same situation as me (i got 58 on the spec, 60 on june 10, 62 on jan 11 and 60 on june 11)...

If you come up with a way around the ambiguous/vague/general horrendous nature of the exam questions please let me know! Its killing me :frown:

Reply 795

otrivine

hi can anyone ask me questions from chapter 1

Reply 796

Fizzo

Original post by walkbesideme

a) 9.75%
b) 0.95
c) 0.05
d) 190
e) random mating, no genetic drift, no selective advantage, no migration (2000 people is a large popn size?)

Reply 797

Joseppea

Original post by otrivine

hi can anyone ask me questions from chapter 1

What do homeobox genes do?

Reply 798

--NWzD9--

Original post by Fizzo

a) 9.75%
b) 0.95
c) 0.05
d) 190
e) random mating, no genetic drift, no selective advantage, no migration (2000 people is a large popn size?)

Wouldn't your answer to question b) be assuming that all the 195 people were homozygous dominant. The disorder is dominant, so how would you be able to tell how much of the 195 were heterozygous and how much were homozygous dominant. For the answer to be correct, you would have had to said in the question that all the 195 were homozygous dominant