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A cry for help in terms of the IBO

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A cry for help in terms of the IBO

Postby asecond » Sat Jul 12, 2008 4:12 am

Hey peoples :D

Just wondering if anyone can answer some of these questions for me cos honestly i haven't got a clue.
choose a letter that is most appropriate and correct :wink:

1. how do enzymes speed up reactions
a.they increase activation energy-I know this is so not right
b.they make reaction occur only in one direction-um not sure
c.they cause random collisions to occur more frequently-most likely but still not sure
d.They bring reactants into contact with each other.

2.What are sieve tubes?

3.what is the main carbohydrate translocated in the sieve tubes of a flowering plant

4.what is a lignified wall and how does it prevent xylem vessels from collapsing-or maybe it doesn't-help :shock:

5. Does a mammalian heart pump equal volumes of blood at equal pressures?

Thankx-not sure if it's in the right forum but oh well :mrgreen:
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Postby MisterATP » Sat Jul 12, 2008 6:20 am

1. d. Enzymes bring reactants with each other. If enzymes don't participate in reaction, the probability to collide reactants in proper position is pretty low. ( this is very important in reaction when reactants are very ,,diffusive '').
5. When diameter of blood vessel suddenly decreases, the blood pressure increases (at the constant blood volume). But organisms regulate blood pressure by reduction of blood volume or by increasing total volume of circulatory system (changing diameter of blood vessels). So blood volume is directly proportional to blood pressure.

Others questions are very easy so wikipadia helps you. :)
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Re: A cry for help in terms of the IBO

Postby asecond » Tue Jul 15, 2008 5:57 am

Thanks misterATP I totally owe you one
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