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AQA BIOL2 Biology Unit 2 Exam - 26th May 2011

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Reply 280
Original post by asim1993
Can anyone explain how to work out magnification and actual size? i cant remember how to do it


Magnification = actual/ object.
actual = magnification X object.

:smile:
Reply 281
Any predictions on what may come up people? :smile:
Reply 282
Original post by xkate1019x
Haemoglobin

Are my Facts correct? I'm a bit unsure on my termonology...

- Haemoglobin is a protein
- It is made up of 4 polypeptide chains (quartenary structure)
- Each polypeptide has a haem group (non protein ), which contains iron
- It is hard for oxygen to bind with haemoglobin but when the first haem binds to oxygen, the structure of the polypeptides change to make the haemoglobin have a high affinity for oxygen.
- A haemoglobin with a high affinity for oxygen takes up oxygen more easily, but released it more readily. (e.g. in the lungs)
- when one oxygen molecule is released from the haem group, it changes the shape of the haemoglobin structure, and makes it easier for the other 3 to be released, giving it a low affinity for oxygen
- a low affinity for oxygen means the haemoglobin takes oxygen up less easily but released it more readily easily (e.g. in a quickly respiring muscle)

Thanks in advance :smile:


all good except when haemoglobin is at the lungs its has a high affinity for oxygen thus it asscoiates with o2 more readily yet dissociates less readily. Note that its the presence of co2 at the muscles that lowers Hb affinity for oxygen.
lower affinity for oxygen means that when it unloads it, it unloads it easier. am i correct ??
Are these true and if so, is it part of what we need to know?

"When the first haem binds to oxygen, the structure of the polypeptides changes to make the haemoglobin have a high affinity for oxygen."

"When one oxygen molecule is released from the haem group, it changes the shape of the haemoglobin structure, and makes it easier for the other 3 to be released, giving it a low affinity for oxygen."
Original post by James A
lower affinity for oxygen means that when it unloads it, it unloads it easier. am i correct ??


Yea you are correct.:smile:
How's everyone revising for this exam? because I'm struggling juggling my subjects.
I have an exam the day before Biol2 and two exams in the morning before Biol2... kill me now:frown:
Original post by SugarLips.
How's everyone revising for this exam? because I'm struggling juggling my subjects.
I have an exam the day before Biol2 and two exams in the morning before Biol2... kill me now:frown:


unlucky you, i got maths in the morning and biol2 in the afternoon, but your timetable is deadly, what subjects you doing ??
Original post by SugarLips.
How's everyone revising for this exam? because I'm struggling juggling my subjects.
I have an exam the day before Biol2 and two exams in the morning before Biol2... kill me now:frown:


I got...Chem1 tomorrow, then day off, then general studies paper teehee), then on thurs afternoon biol2 and then friday I got economics unit 2 and chemistry unit 2! And it's my leavers day! :frown:
Reply 289
Hello everyone!

I was revising today, and realised basically I understand why there is the first cell division in meiosis. But why have a 2nd?

The first stage created 2 haploid cells as far as I can make out, and then by dividing again, doesn't the 4 cells just get one chromatid from each chromosome? How does this work, and surely when they fuse in fertilisation there would just be two lots of 23 chromatids fusing, whereas what is wanted is two lots of 23 chromosomes fusing in fertilisation to get 23 homologous pairs?

What am I missing?

Any help appreciated, thanks!
Reply 290
Original post by aleema1992
Going good for bio not other subjects wa bou u?
u prepared for this thursdaii


not fully prepared on these topics :- variation, antibiotic resistance and biodiversity.i have read and understand but i feel am not confident to answer HSW que. do you have any exam questions related to this topics to help me out...:smile:
Original post by george424

Original post by george424
Hello everyone!

I was revising today, and realised basically I understand why there is the first cell division in meiosis. But why have a 2nd?

The first stage created 2 haploid cells as far as I can make out, and then by dividing again, doesn't the 4 cells just get one chromatid from each chromosome? How does this work, and surely when they fuse in fertilisation there would just be two lots of 23 chromatids fusing, whereas what is wanted is two lots of 23 chromosomes fusing in fertilisation to get 23 homologous pairs?

What am I missing?

Any help appreciated, thanks!


The first division will form two intermediate haploid cells in which both of them will contain 23 chromosomes, with each chromosome having 2 chromatids and so a total of 46 chromatids in each of these 2 cells.

Now the second division occurs, in this the 23 chromosomes with 2 chromatids split to form 2 separate chromatids. These chromatids are now referred to as chromosomes hence forming 4 cells each containing 23 chromosomes.

Main Point: When Chromatids split from the chromosome they become 2 separate chromosomes.

I hope you understand now.:smile:
(edited 12 years ago)
Reply 292
Anyone got the Nelson Thornes textbook,go to page 192

Is this topic even in the spec? I've never seen a question on this ever, not even on the old specification papers
Reply 293
Original post by therapist_1
The first division will form two intermediate haploid cells in which both of them will contain 23 chromosomes, with each chromosome having 2 chromatids and so a total of 46 chromatids in each of these 2 cells.

Now the second division occurs, in this the 23 chromosomes with 2 chromatids split to form 2 separate chromatids. These chromatids are now referred to as chromosomes hence forming 4 cells each containing 23 chromosomes.

Main Point: When Chromatids split from the chromosome they become 2 separate chromosomes.

I hope you understand now.:smile:


very well done ive always been wondering this because the officl book was so confusing but it doesnt usually come up, maybe concept is gd tohugh :smile:
Reply 294
Original post by Nuss
Anyone got the Nelson Thornes textbook,go to page 192

Is this topic even in the spec? I've never seen a question on this ever, not even on the old specification papers


yes it is
Reply 295
Original post by kingsmod1
yes it is


Could anyone direct me to some questions on it? Can't find any
Reply 296
Original post by Nuss
Could anyone direct me to some questions on it? Can't find any


how does water enter xylem and how does actice transport of salt help ????

Explain and describe lol
Reply 297
Oh crap, wrong page, Nelson Thornes textbook,go to page 134

Never seen a question on it
(edited 12 years ago)
Original post by kingsmod1
how does water enter xylem and how does actice transport of salt help ????

Explain and describe lol



Once water has entered the protoplast of the endodermal cells, they will actively pump ions and salts into the xylem by active transport. This will create a water potential gradient, because the water potential of the xylem will decrease and there will be a higher water potential in the endodermal cells. Water will then move down a water potentail gradient by osmosis into the xylem. :biggrin:

HOPE THIS HELPS!
Reply 299
Original post by Kandy_Kain_94
Once water has entered the protoplast of the endodermal cells, they will actively pump ions and salts into the xylem by active transport. This will create a water potential gradient, because the water potential of the xylem will decrease and there will be a higher water potential in the endodermal cells. Water will then move down a water potentail gradient by osmosis into the xylem. :biggrin:

HOPE THIS HELPS!


nice answer but Nuss was meant to answer that LOL

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