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AS Biology P1 MCQs Preparation Thread

Jaf

Jaf

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Soldier313 said:
isn't it loaded into the companion cell via active transport and then from the companion cell to sieve tube by via plasmodesmata by diffusion?
Or am i mixing up things here?:unsure:
Click to expand...
Yes, that's how they are loaded at the source but the point is that the sources are the photosynthesising leaves, while the sinks are other parts of the plant, like the roots, storage organs. So, when the sugars are loaded into the sieve elements of the leaves, this means that there is more solute in the phloem sap. If you look at my answers above about solute potential is related to water potential, I have said solute potential is always negative, meaning more solute REDUCES/DECREASES water potential. The key here, to avoid confusion, is to understand that solute concentration is inversely proportional to water potential, and increasing it reduces water potential.
 
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sarahnafea

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During excercise tidal volume increases and this will decrease Inspiratory Reserve Volume (i.e. the volume of air which u could inhale but dont) - in this case, volume X. Same goes for volume Y. Thing of Reserve Volumes as a Bank of air. When u excercise u take loans of air from ur reserve and this loan is what increases ur tidal volume. Oh and thanks for ur reply up there :)
 
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Nibz

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Soldier313 said:
just checked the er and it said vital capacity cannot increase, it's just the tidal vol that increases
Click to expand...
That's what I said.

"For TIDAL VOLUME to increase, X and Y will have to decrease."
 
Soldier313

Soldier313

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Jaf said:
Yes, that's how they are loaded at the source but the point is that the sources are the photosynthesising leaves, while the sinks are other parts of the plant, like the roots, storage organs. So, when the sugars are loaded into the sieve elements of the leaves, this means that there is more solute in the phloem sap. If you look at my answers above about solute potential is related to water potential, I have said solute potential is always negative, meaning more solute REDUCES/DECREASES water potential. The key here, to avoid confusion, is to understand that solute concentration is inversely proportional to water potential, and increasing it reduces water potential.
Click to expand...
thanx, that really helped:)
 
Soldier313

Soldier313

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sarahnafea said:
During excercise tidal volume increases and this will decrease Inspiratory Reserve Volume (i.e. the volume of air which u could inhale but dont) - in this case, volume X. Same goes for volume Y. Thing of Reserve Volumes as a Bank of air. When u excercise u take loans of air from ur reserve and this loan is what increases ur tidal volume. Oh and thanks for ur reply up there :)
Click to expand...
that really helped, jazakallah:)
 
I

Ineedhelp

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can someone please answer my questionss
1) What to T killer and T helper cells do ?
2) does the loading of sucrose in the phloem seive tube require active transport? or massflow? :S
 
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