Quote:
|
Originally Posted by penguin Interesting discussion, and good posts 419  , but are you sure that we are interested only in IAA? |
Ah, good point penguin! I got so caught up in The Fool's questions about auxins, I forgot to go into anything else too much...
Quote:
|
Originally Posted by penguin Going back a few posts, there is considerable confusion about the "dark cycle" reactions. The Calvin Cycle takes place in the stroma of the chloroplast, and is perhaps better referred to as the "light-independent process".
The light-dependent reactions, which occur in the thylakoid membrane of the chloroplast, convert light energy to chemical bond energy of ATP & NADPH.
The light-independent process uses these products of the light reactions to reduce CO2 to C6H12O6 (glucose). |
Hmm.....now you are taking me back a few semesters...(can you believe they call this stuff
general biology?!?) But yes, you are correct....I forgot that cellular respiration
wasn't part of the "dark" (or as you so aptly called it, "light-independant") cycle. Since you seem very educated on the processes already, I'm just going to reiterate (with some nice pics and diagrams) for those out there still curious.
Photsynthesis converts solar energy (light) into the chemical energy of a carbohydrate. This is the formula for photosynthesis:
Solar energy + 6CO2 + 6H2O ---> C6H12O6 + 6O2
There are 2 cycles involved in photosynthesis, as I (and penguin) stated:
light-dependant reations, and light-independant reactions. BOTH of these are involved in PHOTOSYNTHESIS, as penguin pointed out. (Not what I said earlier: that the dependant reations were photosynthesis, and the independant reations were respiration.....not true).
The
light-dependant reactions consists of
photosystem I (cyclic phosphorylation, which produces ATP (energy)), and
photosystem II (non-cyclic electron transfer, which splits water molecules to harvest electrons, and produces ATP and NADPH).
The
light-independant reactions is also called the
Calvin Cycle (again, as penguin pointed out), and basically uses the energy (ATP and NADPH) produced in the dependant reactions to reduce CO2 into glucose.
Check out this diagram:
This is all that happens in the "dark" cycle of plants.
Now this is where I became confused earlier. Cellular Respiration is almost like the "opposite" of photosynthesis. You can see this when you look at the formula for respiration:
C6H12O6 + O2 ---> CO2 + H20 + chemical energy (ATP)
You can see the reactants are the same as the products in photosynthesis, and vise versa.
Cellular respiration is where most of a plants chemical energy (ATP) is manufactured. Respiration consists of 4 phases:
Glycolysis (yields 2 ATP),
Pyruvate Oxidation (oxidation reaction; pyruvate is a product of glycolysis),
Krebs Cycle (yields 2 ATP),
Electron Transport Chain (yields 32-34 ATP)
The net ATP molecules produced from one cycle of cellular respiration is 36-38.
As you can see, the main manufactuer of ATP is the Electron Transport Chain (ETC). This is located in the cristae of mitochondria, and is a series of protien carriers. Electrons carried by NADH and FADH2 enter the ETC, and as a pair of electrons is passed from carrier to carrier, energy is released and is used to form ATP molecules by
oxidative phosphorylation.
This is where plants get most of their chemical energy from. As penguin said, without photosynthesis (the formation of glucose), cellular respiration could not happen. So by keeping the lights on 24/7, we are allowing photosynthesis to occur all the time, thus allowing more energy to be manufactured quicker.
Here's a diagram of how photosynthesis and cellular respiration work together:
On the left is photosynthesis ("light" cycle at the top, "dark" cycle - the calvin cycle - at the bottom), and on the right is cellular respiration. As you can see, these two go hand in hand.
Quote:
|
Originally Posted by penguin Both the light reactions and the dark cycle (anabolic processes) are part of photosynthesis, occur in the chloroplast, and thus occur only in photosynthesizing tissues. This produces the energy (stored as bond energy of carbohydrates) that fuels plant metabolism and growth. |
He said it.
Quote:
|
Originally Posted by penguin However, the benefit of this increased growth rate must be weighed against the increased cost of electricity. There is a difference between maximum growth and optimized growth. This optimum photoperiod is somewhat crop- and latitude-specific. |
Well, this may be accurate, but when I think of "optimizing growth", I don't factor in electrical costs and yada yada yada. To me, optimizing growth is all about the ladies. Money should play no part in how well we "optimize" their situations. When you bring electricity and other factors into the equation, I consider that to be the most
efficient growth, but not
optimized. To me, optimized growth and maximum growth are one in the same. We cant become ignorant and keep thinking of ourselves (money) if we want to give out girls the best. Just my opinion though.
So, in a nutshell again (and to tie it all together), photosynthesis includes both light-dependant and light-independant reactions. The outcome of photosynthesis is glucose, which is then used by cellular respiration to manufacture chemical energy for the plant (to grow). The plant then uses this energy (in conjuntion with the IAA auxins) to promote fast, healthy root and shoot growth. Neither the production of this chemical energy, nor the production/use of auxins, depends on a "dark" cycle, and thus, plants CAN be kept in 24 hours of light with no bad effects.
So there we have it. Thank you penguin for the nice point-outs of my mistakes. I like a person who makes me pick my brain! Sorry for the confusion, folks.
