When there is no sunlight most plants can't do too much. The sunlight is what actually gives the engergy to split the water molecules into oxygen, so without it no oxygen is produced, and without the high engergy elections formed in this process the plants cannot regenerate NADPH which is required for carbon fixation of the Calvin cycle. So as a result no oxygen gets produced and no carbon dioxide gets used.

 

The second question I believe is because all( almost all) plants only have stoma on the bottom of the leaves. Hope that helps.

i need some help here.

 

Explain why, at certain times of the day, there is no net movement of oxygen or carbon dioxide through stomata, even though ther are open.

 

Well, my guess is that the food produced cause the guard cells to become turgid, etc, so, it swells and causes the stomata to open. But, when i re-read the question several times, i realised that the answer is somewhat incorrect.

 

Another related qn:

Explain why most water loss usually occurs from the lower surface of a leaf.

 

My guess is that, is that the opening, the stomata iis at the lower surface of the leaf. So, the water leaves there/

 

I'm not lazy or that i depend on other for HW answers or whatso ever. I just (most of the time) have difficultly understanding the biology of plants. No matter how hard i try. It just makes no sense. Therefore, i have difficulty understanding the theory about plants... the transport system thing... and how they make food and stuff.

 

Thanks for anybody who helps.

 

P.S. I never do well for questions related to plants. Especially in exams.

eh... i don't get what you mean in the frist paragraph. what is NADPH... and what calvin cycle?

 

Heh... i thought about it... maybe the ans is like

the rate of respiration is equal to the rate of photosynthesis...

Thus, there is no net movement... Because the amount of CO2 and O2 produced is equal...so there is no diffusion gradient..

 

Anyone to verify my answer? Seriously, does it make sense?

Yes, that makes sense.

 

It's that "net" in the question that gives it away

Sayonara³ said in post #4 :

It's that "net" in the question that gives it away

 

Why do you say so? What does the "net" thing tell?

The "net" says that there IS movement of CO2 and O2, but that OVERALL there is no movement, like you stated.

What he said ^

oH.. GOT it.. THANKS SAYOOOoooo, And BLIKEEEEeee. and FLex. i completed the question

SO MUCh.