OCR AS Biology (F211) - Jan 2013.

Does anyone have a set of questions or some sort of test only on the Plants section of the Unit? That's my weakest point and I need some more practice on that. :frown:

Thanks.

yes this would be really helpful im stressing about plants! there just so muc to learn and ive done load of revision on the heart

Reply 581

Raine6

Hey guy's I know this is really silly of me to ask I haven't revised for this exam one bit. My outlook on life has changed and I've decided to revise haha and get at least a b,any help / advice/tips xxxx I understand most of the concepts just don't seem to remember them Pleaasseee help xxx

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Reply 582

Dugald

Original post by Raine6

Hey guy's I know this is really silly of me to ask I haven't revised for this exam one bit. My outlook on life has changed and I've decided to revise haha and get at least a b,any help / advice/tips xxxx I understand most of the concepts just don't seem to remember them Pleaasseee help xxx

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Don't worry, you still have long enough to significantly boost your grade. My advise to you would be to go through the text book, reading it page by page and maybe making a few brief notes (brief due to limited time). Then do as many of the past papers as you possible can and going through the mark schemes for them learning to give the examiner exactly what they want.

Reply 583

simonb451

Original post by Raine6

Hey guy's I know this is really silly of me to ask I haven't revised for this exam one bit. My outlook on life has changed and I've decided to revise haha and get at least a b,any help / advice/tips xxxx I understand most of the concepts just don't seem to remember them Pleaasseee help xxx

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Ive revised solidly for 2 months and still dont feel like im even going to get a C as i dont get cell signalling or the potometer.

Reply 584

SuperMushroom

9

Original post by simonb451

Ive revised solidly for 2 months and still dont feel like im even going to get a C as i dont get cell signalling or the potometer.

For cell signalling just know this:

Process that leads to communication and coordination between cells, e.g. hormones binding to their receptors on the
cell surface membrane.

Its that simple

Reply 585

manchesterunited15

I'm doing this January 09 paper, and question 3c needs a table but it's been removed due to copyright, does anyone know what the table is or where to find it?

PLEASE HELP ME

(edited 11 years ago)

Reply 586

cxross

Does anyone know any good documentaries which apply to the course which i can find online? thanks, Ross. :smile:

Reply 587

morvenrkr

Original post by manchesterunited15

I'm doing this January 09 paper, and question 3c needs a table but it's been removed due to copyright, does anyone know what the table is or where to find it?

if you let me know how to uplaod the paper i can give you it :P

Reply 588

manchesterunited15

Original post by morvenrkr

if you let me know how to uplaod the paper i can give you it :P

could you just like write out the table please? :smile:

It would be a great help

Reply 589

Sophie Hurt

4

I'm finding the heart tricky
Can someone explain the cardiac cycle and how the heart is coordinated
Thanks :smile:

Reply 590

alicevictoriaxxx

Original post by Sophie Hurt

I'm finding the heart tricky
Can someone explain the cardiac cycle and how the heart is coordinated
Thanks :smile:

I've messaged you :-)

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Reply 591

Jrph

Original post by manchesterunited15

could you just like write out the table please? :smile:

It would be a great help

Here's the table for the question you asked for...

(edited 11 years ago)

Table.png81.2KB

Reply 592

kram96

Original post by zoep23

Translocation is the movement of assimilates (sugars e.g sucrose) from where it is produced in the source, to where it is removed in the sink. There are 2 parts to the translocation thing, first active loading, then the actual movement of the sucrose down the phloem.
In active loading (loading the sucrose into the Phloem at the source)
- H+ ions are actively transported out of the companion cells using ATP.
-This produces a H+ ion concentration gradient back into the companion cell.
- H+ ions move back into the companion cells and bring sucrose molecules with them through co transporter proteins by facilitated diffusion
-The concentration of sucrose is now higher in the companion cells than in the sieve element
-Sucrose moves into the sieve element by diffusion down a concentration gradient.

The second part is the actual transport:
-Once sucrose has been actively loaded into the sieve element, this reduces the water potential within the sieve element
-So, water moves into the sieve element by osmosis
-This increases the hydrostatic pressure at the top of the sieve element. Water moves down the phloem from an area of high hydrostatic pressure to low at the sink.
-At the sink sucrose is removed from the sieve element by active transport, this reduces the water potential of surrounding cells so water moves out of the sieve element into the surrounding cells by osmosis.

Thanks a lot, very helpful

Reply 593

Dugald

Original post by simonb451

Ive revised solidly for 2 months and still dont feel like im even going to get a C as i dont get cell signalling or the potometer.

Cell signalling is to do with receptors on the surface of the cell. They are usually made of glycoproteins and glycolipids. They form a receptor site that is comlementary to the shape of a paticular signal molecule/hormone. They bind together and initiate a response from the cell.

Reply 594

manchesterunited15

Original post by Jrph

Here's the table for the question you asked for...

Thankyou!

Reply 595

Dugald

Original post by simonb451

Ive revised solidly for 2 months and still dont feel like im even going to get a C as i dont get cell signalling or the potometer.

A potometer is used to measure the rate of transpiration but isn't totally reliable because it only measures water uptake not water loss from areal parts of the plant.

When setting it up you have got to make sure that there are no leaks, air bubble, cut the stem underwater (to remove any air in the xylem that could cause blockages), set up the apparatus under water and ensure that the leaves of the plant are dry.

You use the potometer by measuring how far along the tube the water bubble travels over a set time, from this you can work out how much water it has taken up taking into account the cross sectional area of the tube.

You use the potometer to measure rates of transpiration of a plant under different conditions.

Reply 596

Pink amyapple

4

How are you guys finding this:
describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the bohr effect)

I'm finding it kinda confusing :/

Reply 597

SuperMushroom

9

Original post by Pink amyapple

How are you guys finding this:
describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the bohr effect)

I'm finding it kinda confusing :/

describe the role of haemoglobin in carrying oxygen and carbon dioxide;
Oxygen
Haemoglobin consists of four subunits. Each subunit consists of a polypeptide and a haem group.
The haem group contains one iron ion, Fe2+. Because the iron ion attracts oxygen, it is said to have
an affinity for it. A molecule of haemoglobin, and therefore a red blood cell, can hold four
molecules of oxygen.
Haemoglobin can take up oxygen in a way that produces an S-shaped curve. This is called the Oxygen
Dissociation Curve. At a low oxygen tension the haemoglobin does not readily take up oxygen. This is
because it is difficult for the oxygen molecule to reach the haem group, due to it being in the centre of the
blood cell.
When the oxygen tension rises, the diffusion gradient into the haemoglobin molecule steeply rises. Once
one molecule of oxygen has associated with a haem group, the shape of the haemoglobin molecule slightly
changes, making it easier for the second the third molecules of associate. The change in the shape is known
as the ‘conformational change’.
But, once the haemoglobin molecule contains three oxygen molecules, it is difficult for the forth to associate
with the last haem group. This means that it is difficult to achieve 100% saturation, even at high oxygen
pressures. A consequence of this is that the curve levels off again, meaning that the graph is S-shaped.
Carbon Dioxide
5% dissolves in the plasma
10% combines with haemoglobin to form carbaminohaemoglobin
85% is transported as hydrogencarbonate ions
As Carbon dioxide diffuses into the blood, some of it enters the red blood cells and
combines with water to form carbonic acid, catalysed by carbonic anhydrase.
CO2 + H2O → H2CO3
This carbonic acid then dissociates to form Hydrogen ions and Hydrogencarbonate
ions
H2CO3→ H+ + HCO3
-
The Hydrogencarbonate ions diffuse out of the red blood cell. The charge in the
red blood cell is maintained by the Chloride Shift; the movement for Chloride ions
into the cell.
Hydrogen ions could cause the contents of the cell to become very acidic, so the
haemoglobin acts as a buffer. They oxyhaemoglobin dissociates, and the hydrogen
ions are taken up by the haemoglobin to form haemoglobonic acid.

describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide
levels (the Bohr effect); `
When tissues are respiring more, there will be more carbon dioxide, and therefore more Hydrogen ions. This
means that more oxygen will be released from oxyhaemoglobin into the tissues. So, when more carbon
dioxide is present, the oxyhaemoglobin dissociation curve shifts down and to the right.

explain the significance of the different affinities of fetal haemoglobin and adult haemoglobin for oxygen
Fetal haemoglobin has a higher affinity for oxygen than the haemoglobin of its mother. This is because the
fetal haemoglobin must be able to ‘pick up’ oxygen from the haemoglobin from its mother. This reduces the
oxygen tension within the blood fluid, so the maternal blood release oxygen.

The oxyhaemoglobin dissociation curve for fetal haemoglobin is to the left of the curve for adult
haemoglobin.

Reply 598

joe1545

14

Original post by Pink amyapple

How are you guys finding this:
describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the bohr effect)

I'm finding it kinda confusing :/

From what we know regarding Haemoglobin and CO2 we can apply this too the dissociation curves.
The more CO2 present the more H+ ions produced the more the oxygen is forced out of the cell.
Hence the more the oxygen is pushed out means that at when there is a high concentration of CO2 there will be a low saturation of Oxygen.
Hence the dissociation curve will be down and to the right of the maternal curve.
We can just reverse this and say that the lower the concentration of CO2 the less the oxygen is pushed out of the cell hence it will be up and the left of the maternal curve.

Reply 599

theworld

PLEASE HELP

m very worried about this exam. Ive revised 3/4, everything except the section 'Transport in Plants', which I know nothing about. Ive hardly done any past papers except those at school. (about 2)

What should I do at this point

OCR AS Biology (F211) - Jan 2013.

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