Photosynthesis and cellular respiration

[bio_intern]

Please can you explain it slowly and simply! I have an exam tomorrow and do not have any idea how it all works in plants; why do they turn CO2 + H2O into C6H12O6 + O2 just so they can turn it back again when they respire? It makes no sense to me, please explain. I thought I had it right, then I read these pages with all the details and I'm lost!
Hope you get back to me quick, thanks in advance!

-I have split this from the cellular respiration topic since it was a different problem. Also i have relocated it to th Botany forum because it concernes plants. MrMistery-

[MrMistery]

Ok... so think of it like this: why do you keep food in your fridge instead of going to the market every time you are hungry? Because the store might close or you might get hungry at night when the store is closed and you will starve.
In the same way, plants need to have ATP at all time: even at night! They need energy to carry out their processes at all times and the only way that they can make supplies is to turn solar energy into glucose through photosynthesis and then run it through the Krebs cycle to get the energy

[mith]

<reeealllly extended metaphor>
So you buy and install this solar cell which absorbs sunlight and converts it to electricity for your house. You get all excited the next morning and cancel your regular grid electricity. "NO more electric bills!" you scream.

Now, it's night, your solar cell can't absorb light because there is none except for that teeny moonlight. Your house powers down. The appliances shut off. Your heater coughs and dies. The house becomes cold. Your refrigerator stops working and things start rotting. You hear noises and wonder why your electrified fence doesn't hum anymore. The next thing you know, vandals have come in and bashed your head in. They leave you half dead on the street.

You wake up from the scariest nightmare ever and vow that you will install some batteries to store the electricity you get in the daytime so you can keep things running at night.

</reeealllly extended metaphor>

[MrMistery]

Reeeeeeally extended, mithril...

[Jelanen]

Umm....yeah.....

-Jelanen

[clarence]

Being concise, it can be said like this. All physical systems, living organisms included, have a tendency to become disordered, to increase in entropy. Living organisms have a high degree of order and regularity, maintained by the constant input of energy. In order to maintain this order, and in turn prevent death in the molecular sense, the energy from the sun is converted to glucose, a very stable molecule. This molecule can then broken down to provide energy when the need arises and prevent entropy (disorder) or death from occuring.

[mith]

My spidey sense is tingling, I think kyle is going to post here soon

[MrMistery]

Lool.. You are right. When someone says the word "entropy" Kyle comes rushing along...

[Poison]

Wow!!! I still can not see Kyle around.

[MrMistery]

Kyle is busy setting up his internet at home. Give him time...

[biostudent84]

LOL!

I think my work here is done

But just in case.....

[rant]
THIS IS A FACT! LEARN IT!

Enthalpy (heat energy) is balanced by ENTROPY (disorder). Enthalpy wants to be low, and Entropy wants to be high. However, when one is high, the other is high, and vice-versa. Run a search for this, as I've grown tired of explaining it (I must have done so a number of times, and should be easily found)......they are balanced, so nothing will ever have the lowest Enthalpy, nor the highest Entropy.....

Kyle

[MrMistery]

Yeah, i knew that already from the other 100 posts you made on this matter. Well, now i know it from 101 posts
Plus, it is what we study in 9th grade chemistry