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photosynthesis

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photosynthesis

Postby stuffmuffin » Fri May 12, 2006 11:00 am

hey there,
i wondered this question when we did photosynthesis in class today:
when plants carry out photosynthesis, they will need water right?
my question is, if plants get water form their roots, how do they manage to transport water from the roots to the leaves, if it is against gravity?

hope someone could help me with this....
thanks~!! :D
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Postby MrMistery » Fri May 12, 2006 4:48 pm

sucktion force of leaves, radicular pressure, capillary ascending force, cohesion, adhesion. lots of stuff...
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Postby SU_reptile » Sat May 13, 2006 9:29 pm

sucktion force of leaves, radicular pressure, capillary ascending force, cohesion, adhesion. lots of stuff...


As far as I remember the other thing that brings about water uptake is carbohydrates production taking place while photosynthesis proceeds. It is due to the different contentration of carbohydrates between root and leaf cells (principles of diffusion say that water move from the place that has lower concentration to the one where higher concentration occurs - because there is "lower concentration" of water).
In spring when there are no leaves, radicular pressure occurs so upper parts of the plant is supplied in water. Then, when leaves are present, epidermal cells (guard cells with stomata) provide transpiration that causes the sucking force of leaves. Adhesion refers to the capillary ascending force and cohesion keeps water molecules together.
It is also worth remembering that water management in roots is provided by endodermis.
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Postby stuffmuffin » Wed May 24, 2006 7:09 am

Enzymes are substances that speed up the rate of reactions, without being used up in the reaction. Each of the many reactions in photosynthesis is controlled by a particular enzyme.
What does each of these enzymes contribute to the process of photosynthesis?
- ADP
- ATP
- NAD
- NADH2
- co-enzymes
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Postby yamukeya » Thu May 25, 2006 12:33 pm

Water movement-At the young growing tip of a root are numerous thin hairs.These are in close contact with the soil particles whic may have water on them.The root hair contains a vacuole with cell sap and has cytoplasm,therefore osmosis will take place;the soil water will be drawn in to make the vacuole more dilute.
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Postby SU_reptile » Thu May 25, 2006 5:01 pm

    - ADP - it reacts with Pi (phosphate group) giving ATP (in photosynthesis the process is called photophosphorylation)
    - ATP - it is producet in photophosphorylation and it is required to reduce phosphoglyceric acid (PGA) to phosphoglyceraldehyde (PGAL) and then to reconstruct ribulose bisphosphate (RuBP)
    - NAD is used in respiration as hydrogen carrier
    - NADH2 is the reduced form of NAD
    - co-enzymes - NAD, FAD and cytochrome; they are hydrogen carriers and are responsible for transfering hydrogen to cytochrome oxidase


In photosynthesis (light stage) NADP is reduced to NADPH so that it can join ATP in order to reduce PGA to PGAL in Calvin-Benson's cycle (dark stage)
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Postby MrMistery » Thu May 25, 2006 6:10 pm

SU_reptile wrote:As far as I remember the other thing that brings about water uptake is carbohydrates production taking place while photosynthesis proceeds. It is due to the different contentration of carbohydrates between root and leaf cells (principles of diffusion say that water move from the place that has lower concentration to the one where higher concentration occurs - because there is "lower concentration" of water).


What you are talking about is the transport of phloem. Water is taken in by the root through the xylem, which is something completely different. In summer, the main thing contributing to the absorbtion of water is the sucktion force of the leaves. They release water by transpiration and then suck water from the xylem vessels.
Regards,
Andrew
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Postby SU_reptile » Thu May 25, 2006 10:13 pm

What you are talking about is the transport of phloem

Yes yes of course, you're right. I don't know how I could have mixed the pressure flow theory with water uptake in xylem :oops: . Terrible mistake.
Thanks for correcting this anyway :o .
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Postby baikuza » Sat May 27, 2006 12:03 pm

...Then, when leaves are present, epidermal cells (guard cells with stomata) provide transpiration that causes the sucking force of leaves...


you are right, but do not forget that not only by epidermal cells, but also all cell inside the leaf(e.g. palisade, sponge)
that the reason why some plant close the stomata when it goes too hot-too much transpiration, in this case-and some also use the derivate of epidermal cell to roll the leaf so that the transpiration is less than before(e.g. Zea mays).
:wink:
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