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AQA BIOL2~3rd June 2013~AS Biology (Now Closed)
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Original post by Jaydude
To increase the surface area and it's cut under water to prevent air entering the xylem.
Correct me if I am wrong anyone.
Correct me if I am wrong anyone.
Thanks a lot
Original post by SophieL1996
Can anyone explain the apoplastic and symplastic pathway ? thanks
Okay, first off they are both ways of water moving through a plant.
The Apoplastic Pathway
This works by the cohesion tension of water molecules that are pulls water along the mesh-like structure of the cellulose walls toward the endodermis.
At the endodermis the water-proof Casparian Strip prevents the movement of water through the apoplastic pathway, so the water is forced into the cytoplasm to join the Symplastic Pathway.
The Symplastic Pathway
The cytoplasm of adjacent cells in the root are linked by gaps in the cell wall called Plasmodesmata (thin strands of cytoplasm linking cells from the root hair to the endodermis).
Water passes through the Plasmodesmata from cytoplasm to cytoplasm along the water potential gradient across the whole root. The water potential lowers the further from the root it gets.
All movement from root hair cells to endodermis is passive.
Hope it helps
Can someone explain how CO2 enters a leaf (3/4 marks)
Original post by PoorLoser
can someone explain the immunological comparison of proteins to me? I really don't understand it. Thanks!
(Also could you mention what a "serum" actually is?)
(Also could you mention what a "serum" actually is?)
Alright I'll have a crack at it
Just think of serum albunim as a protein.
So what you do is take protein from species A and inject it into species B. Do you remember from unit 1 that proteins in your body have specific antigens so that your body recognises them and knows not to attack them.
Well if you take proteins from A into B, B will recognise from its antigens that it is foreign and create antibodies that are complimentary to the shape of those antigens and destroy them.
Now we take the antibodies created by Species B for the antigens of Species A and inject into Species C.
All we're doing is taking across anitbodies that are specific to antigens in Species A.
Now if we put them in Species C, then the more antigens C has that are similar to A then the more the antibodies will bind with them and destroy, the more they bind with and destroy the more precipitate that is created.
The most important thing to remember to tie it all in is that DNA bases code for amino acids which make proteins and antigens are proteins. So if C and A have similar antigens it is due to the sequences of DNA bases.
Hope that helps! Anymore questions PM me.
Original post by Paulineuh
Root pressure = the pressure that is created when the endodermis actively transports mineral ions into the xylem, lowering its water potential thus as a result as there is a higher water potential in the endodermal cells, water moves by osmosis due to the water potential gradient established. Root pressure is the force that pushes the water up the xylem although not as greatly as transpiration.
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Nice explanation, but I still have one question. Why is it active transport? So what I mean is why does the xylem have a higher concentration of mineral ions?
And where exactly is the pressure created? In the xylem or in the endodermal cell?
Sorry
Original post by Suzanna5678
Can someone explain how CO2 enters a leaf (3/4 marks)
Stomatal pores open in sunlight. Stomata are usually found on the undersides of leaves and they draw in CO2 by diffusion.
I'm not sure how this can be a 3/4 mark question.
Actually I just found a similar question like that and this is what the markscheme says:
1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;
(edited 10 years ago)
Original post by DarkOne
Okay, first off they are both ways of water moving through a plant.
The Apoplastic Pathway
This works by the cohesion tension of water molecules that are pulls water along the mesh-like structure of the cellulose walls toward the endodermis.
At the endodermis the water-proof Casparian Strip prevents the movement of water through the apoplastic pathway, so the water is forced into the cytoplasm to join the Symplastic Pathway.
The Symplastic Pathway
The cytoplasm of adjacent cells in the root are linked by gaps in the cell wall called Plasmodesmata (thin strands of cytoplasm linking cells from the root hair to the endodermis).
Water passes through the Plasmodesmata from cytoplasm to cytoplasm along the water potential gradient across the whole root. The water potential lowers the further from the root it gets.
All movement from root hair cells to endodermis is passive.
Hope it helps
The Apoplastic Pathway
This works by the cohesion tension of water molecules that are pulls water along the mesh-like structure of the cellulose walls toward the endodermis.
At the endodermis the water-proof Casparian Strip prevents the movement of water through the apoplastic pathway, so the water is forced into the cytoplasm to join the Symplastic Pathway.
The Symplastic Pathway
The cytoplasm of adjacent cells in the root are linked by gaps in the cell wall called Plasmodesmata (thin strands of cytoplasm linking cells from the root hair to the endodermis).
Water passes through the Plasmodesmata from cytoplasm to cytoplasm along the water potential gradient across the whole root. The water potential lowers the further from the root it gets.
All movement from root hair cells to endodermis is passive.
Hope it helps
Thanks that helped a lot
could you explain the cohesion-tension theory aswell? As i'm getting confused with it... Thanks!
Original post by SophieL1996
Can anyone explain the apoplastic and symplastic pathway ? thanks
Basically water wants to get from the soil into the xylem vessels. It can do this by 2 methods or 'pathways' called the SYMPLAST PATHWAY or APOPLAST PATHWAY. (Might be useful if you get a labelled diagram showing xylem/root hair cell etc whilst reading this).
Symplast Pathway
In the Symplast pathway, water moves through the CYTOPLASMS of the cells.
Water diffuses along a water potential gradient through PORES between the cells of the Cortex called plasmodesmata. The Cortex is simply all the cells between the Root hair cell and the Xylem vessel.
Apoplast Pathway
In the Apoplast pathway, water moves through the CELL WALLS of the cells.
Water stops at the ENDODERMIS as there is a CASPARIAN STRIP which prevents the water from passing further, making the water pass through a membrane by osmosis down a water potential gradient INTO THE SYMPLAST PATHWAY, which is useful as it prevents harmful substances such as toxins or viruses from entering the xylem vessels as the membrane would not let them past.
--------------------------------------------------------------------
EXTRA
- Water potential in the root hair cell is lowered by the active transport of mineral ions from the soil, hence water can move from the soil into them down a water potential gradient.
Watch this, if you need more help:
http://www.youtube.com/watch?v=TWNtXw-MWtE
(edited 10 years ago)
Original post by Sumi Prakash
Could someone PLEASE explain the formation of tissue fluid and what 'hydrostatic pressure' is?
I'm really struggling and the book is not making any sense whatsoever!
I'm really struggling and the book is not making any sense whatsoever!
Okay!
Just think of hydrostatic pressure as the pressure that forces out tissue fluid from blood plasma.
Now the hydrostatic pressure is created as the lumen of the vessels leading up the capillaries get narrower and narrower. We go from arteries, to arterioles then capillaries (which are very narrow).
This narrowing creates hydrostatic pressure.
And tissue fluid is from blood plasma
Is that clearer?
(edited 10 years ago)
Original post by Sorro10
Basically water wants to get from the soil into the xylem vessels. It can do this by 2 methods or 'pathways' called the SYMPLAST PATHWAY or APOPLAST PATHWAY. (Might be useful if you get a labelled diagram showing xylem/root hair cell etc whilst reading this).
Symplast Pathway
In the Symplast pathway, water moves through the CYTOPLASMS of the cells.
Water diffuses along a water potential gradient through PORES between the cells of the Cortex called plasmodesmata. The Cortex is simply all the cells between the Root hair cell and the Xylem vessel.
Apoplast Pathway
In the Apoplast pathway, water moves through the CELL WALLS of the cells.
Water stops at the ENDODERMIS as there is a CASPARIAN STRIP which prevents the water from passing further, making the water pass through a membrane by osmosis down a water potential gradient INTO THE SYMPLAST PATHWAY, which is useful as it prevents harmful substances such as toxins or viruses from entering the xylem vessels as the membrane would not let them past.
--------------------------------------------------------------------
EXTRA
- Water potential in the root hair cell is lowered by the active transport of mineral ions from the soil, hence water can move from the soil into them down a water potential gradient.
Watch this, if you need more help:
http://www.youtube.com/watch?v=TWNtXw-MWtE
Symplast Pathway
In the Symplast pathway, water moves through the CYTOPLASMS of the cells.
Water diffuses along a water potential gradient through PORES between the cells of the Cortex called plasmodesmata. The Cortex is simply all the cells between the Root hair cell and the Xylem vessel.
Apoplast Pathway
In the Apoplast pathway, water moves through the CELL WALLS of the cells.
Water stops at the ENDODERMIS as there is a CASPARIAN STRIP which prevents the water from passing further, making the water pass through a membrane by osmosis down a water potential gradient INTO THE SYMPLAST PATHWAY, which is useful as it prevents harmful substances such as toxins or viruses from entering the xylem vessels as the membrane would not let them past.
--------------------------------------------------------------------
EXTRA
- Water potential in the root hair cell is lowered by the active transport of mineral ions from the soil, hence water can move from the soil into them down a water potential gradient.
Watch this, if you need more help:
http://www.youtube.com/watch?v=TWNtXw-MWtE
Could you also explain cohesion-tension? Thanks
Original post by SophieL1996
Thanks that helped a lot could you explain the cohesion-tension theory aswell? As i'm getting confused with it... Thanks!
could you explain the cohesion-tension theory aswell? As i'm getting confused with it... Thanks!Water is moving up against gravity in plants, cohesion and tension help with this.
Water evaporates from the surface of the cell walls of the spongy mesophyll cells (known as transpiration) and water leaves through the stomata.
This loss of water lowers the water potential of the spongy mesophyll cells causing water to move out of the xylem vessel into the surrounding cell down a water potential gradient by osmosis.
Inside the xylem vessels, the water molecules are bonded together by hydrogen bonds (called Cohesion) forming continuous columns of water.
The cohesion of water molecules ensures that as water is lost at the leaf by evaporation, it pulls the column of water further up the stem to replace the water molecules being lost. This creates a tension (suction) inside the xylem vessels
This is basically, the cohesion-tension theory.
(edited 10 years ago)
Original post by WavingFLag
Okay!
Just think of hydrostatic pressure as the pressure that forces out tissue fluid from blood plasma.
Now the hydrostatic pressure is created as the lumen of the vessels leading up the capillaries get narrower and narrower. We go from arteries, to arterioles then capillaries (which are very narrow).
This narrowing creates hydrostatic pressure.
And tissue fluid is from blood plasma
Is that clearer?
Just think of hydrostatic pressure as the pressure that forces out tissue fluid from blood plasma.
Now the hydrostatic pressure is created as the lumen of the vessels leading up the capillaries get narrower and narrower. We go from arteries, to arterioles then capillaries (which are very narrow).
This narrowing creates hydrostatic pressure.
And tissue fluid is from blood plasma
Is that clearer?
Yes. So what is ultrafiltration? Also how does the tissue fluid return to the circulatory system?
Original post by Sorro10
Water is moving up against gravity in plants, cohesion and tension help with this.
Water evaporates from the surface of the cell walls of the spongy mesophyll cells (known as transpiration) and water leaves through the stomata.
This loss of water lowers the water potential of the spongy mesophyll cells causing water to move out of the xylem vessel into the surrounding cell down a water potential gradient by osmosis.
Inside the xylem vessels, the water molecules are bonded together by hydrogen bonds (called Cohesion) forming continuous columns of water.
The cohesion of water molecules ensures that as water is lost at the leaf by evaporation, it pulls the column of water further up the stem to replace the water molecules being lost. This creates a tension (suction) inside the xylem vessels
This is basically, the cohesion-tension theory.
Water evaporates from the surface of the cell walls of the spongy mesophyll cells (known as transpiration) and water leaves through the stomata.
This loss of water lowers the water potential of the spongy mesophyll cells causing water to move out of the xylem vessel into the surrounding cell down a water potential gradient by osmosis.
Inside the xylem vessels, the water molecules are bonded together by hydrogen bonds (called Cohesion) forming continuous columns of water.
The cohesion of water molecules ensures that as water is lost at the leaf by evaporation, it pulls the column of water further up the stem to replace the water molecules being lost. This creates a tension (suction) inside the xylem vessels
This is basically, the cohesion-tension theory.
Ahh thanks, could you explain 8b iii as I don't understand it thanks! http://filestore.aqa.org.uk/subjects/AQA-BIOL2-QP-JAN12.PDFhttp://filestore.aqa.org.uk/subjects/AQA-BIOL2-W-MS-JAN12.PDF
Original post by SophieL1996
Thanks that helped a lot could you explain the cohesion-tension theory aswell? As i'm getting confused with it... Thanks!
could you explain the cohesion-tension theory aswell? As i'm getting confused with it... Thanks!No prob
Cohesion Tension Theory is based on the fact that water molecules are polar. The Oxygen atom are slightly negative, and the hydrogen molecule is slightly positive.
As a result there is an attraction between water molecules. The red lines show the Hydrogen Bonding between the individual molecules. They are Cohesive.
So water forms a continuous, unbroken pathway across the mesophyll cells and down the Xylem.
When transpiration takes place, water molecules are being sucked up from the root to the leave, because of the cohesion of the molecules. They stick together. So as water is leaving the surface of the leaves, more water molecules are being drawn up from the root.
This Transpiration Pull puts the xylem under tension, because the water being sucked up.
Thus the name Cohesion-Tension.
It is backed up by the fact that when transpiration rates are at their highest, the diameter of the tree trunk shrinks because there is a negative pressure in the Xylem.
It's not too complicated you just need to remember the main bits.
Original post by Sumi Prakash
Could someone PLEASE explain the formation of tissue fluid and what 'hydrostatic pressure' is?
I'm really struggling and the book is not making any sense whatsoever!
I'm really struggling and the book is not making any sense whatsoever!
Firstly, you need to know that blood in Arteries and Arterioles (Arteries subdivide into Arterioles) is at a high pressure, and at a low pressure in capillaries.
---------------------------------------------------------------------------------------------------------------
At the arterial end of the capillary (end of capillary closer to the Arteriole/Artery), blood is still at a fairly high pressure. This is called Hydrostatic pressure, and it squeezes a fluid called tissue fluid out of pores in the wall of the capillary.
Tissue fluid is plasma without the larger plasma proteins which are too large to fit through pores.
The cells surrounding the capillary are bathed in the tissue fluid and materials are exchanged by direct diffusion between the cells and tissue fluid.
As blood moves along the capillary, the proteins become more concentrated due to the loss of water. This lowers the water potential of the blood. The water in the tissue fluid moves back into the blood by osmosis due to a water potential gradient between the tissue and the blood (this is at the venus end of the capillary).
Any tissue fluid remaining is called lymph which drains into the Lymphatic system and is eventually returned to the blood (lymph is effectively the same as tissue fluid).
Original post by Sorro10
Firstly, you need to know that blood in Arteries and Arterioles (Arteries subdivide into Arterioles) is at a high pressure, and at a low pressure in capillaries.
---------------------------------------------------------------------------------------------------------------
At the arterial end of the capillary (end of capillary closer to the Arteriole/Artery), blood is still at a fairly high pressure. This is called Hydrostatic pressure, and it squeezes a fluid called tissue fluid out of pores in the wall of the capillary.
Tissue fluid is plasma without the larger plasma proteins which are too large to fit through pores.
The cells surrounding the capillary are bathed in the tissue fluid and materials are exchanged by direct diffusion between the cells and tissue fluid.
As blood moves along the capillary, the proteins become more concentrated due to the loss of water. This lowers the water potential of the blood. The water in the tissue fluid moves back into the blood by osmosis due to a water potential gradient between the tissue and the blood (this is at the venus end of the capillary).
Any tissue fluid remaining is called lymph which drains into the Lymphatic system and is eventually returned to the blood (lymph is effectively the same as tissue fluid).
---------------------------------------------------------------------------------------------------------------
At the arterial end of the capillary (end of capillary closer to the Arteriole/Artery), blood is still at a fairly high pressure. This is called Hydrostatic pressure, and it squeezes a fluid called tissue fluid out of pores in the wall of the capillary.
Tissue fluid is plasma without the larger plasma proteins which are too large to fit through pores.
The cells surrounding the capillary are bathed in the tissue fluid and materials are exchanged by direct diffusion between the cells and tissue fluid.
As blood moves along the capillary, the proteins become more concentrated due to the loss of water. This lowers the water potential of the blood. The water in the tissue fluid moves back into the blood by osmosis due to a water potential gradient between the tissue and the blood (this is at the venus end of the capillary).
Any tissue fluid remaining is called lymph which drains into the Lymphatic system and is eventually returned to the blood (lymph is effectively the same as tissue fluid).
Makes a lot more sense now, THANK YOU!
does anyone have the jan 2013 paper?
Hi can someone please give a six mark answer for how insects are adapted for gas exchange? And do you think they can ask a six marker on the symplast or apoplast pathway? Thanks
Do we link apoplastic pathway with the cohesion tension theory ??
Original post by SophieL1996
Ahh thanks, could you explain 8b iii as I don't understand it thanks! http://filestore.aqa.org.uk/subjects/AQA-BIOL2-QP-JAN12.PDFhttp://filestore.aqa.org.uk/subjects/AQA-BIOL2-W-MS-JAN12.PDF
If the cohesion-tension theory is correct, the water must TRANSPIRE first before water moves up the Xylem, and this is shown by the rate of water movement peaking earlier in the day than the rate of water movement in the trunk, as the water can only be moved from down in the trunk once water is transpired, hence water can be pulled up from the tension caused and from the cohesion of water molecules.
(edited 10 years ago)
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