dark reaction ppt
TRANSCRIPT
-
8/11/2019 Dark Reaction ppt
1/13
By: ANAZ. ANATURAL SCIENCE
Candidate
code:13375006
-
8/11/2019 Dark Reaction ppt
2/13
6CO2 +6H2O C6H12O6+6O2
The dark reactions use the energy stored in ATP and
NADPH the light reactions. Carbon atoms from CO2are bonded, or fixed, into
organic compounds = carbon fixation.
THIS OCCURS IN THE STROMA
-
8/11/2019 Dark Reaction ppt
3/13
-
8/11/2019 Dark Reaction ppt
4/13
STEP 1An enzyme (rubisco),
combines CO2with a 5-carbon sugar RuBP
The product, 6-C sugar,immediately splits into
2, -3C molecules (PGA)
PGAPhosphoglycericAcid
-
8/11/2019 Dark Reaction ppt
5/13
Step 2 PGA is converted to
another 3- Carbonmolecule PGAL in a 2 part
process: Each PGA receives a P
group from ATP
The resulting compoundreceives a proton from
NADPH and releases theP, producing PGAL
(ADP & NADP+ return to lightrxn., to make ATP andNADPH)
-
8/11/2019 Dark Reaction ppt
6/13
Step 3
Most of the PGAL is
converted back to RuBP Requires a P from
another ATP
Some PGAL leave andused by plants createorganic compounds
-
8/11/2019 Dark Reaction ppt
7/13
Balance Sheet for Photosynthesis How much ATP & NADH are required to make 1
molecule of PGA from carbon dioxide?
Each turn fixes one CO2
PGAL is a 3-C molecule (takes 3 turns to make eachmolecule)
Each turn of the cycle:
3 ATP ( 2 in step 2 & 1 in step 3) 2 NADPH (step 3)
-
8/11/2019 Dark Reaction ppt
8/13
About 50% made to fuel cell Respiration
Some of the PGAL is used to make amino acids, lipids,carbohydrates like glucose and fructose, glycogen,starch, and cellulose.
-
8/11/2019 Dark Reaction ppt
9/13
-
8/11/2019 Dark Reaction ppt
10/13
Alternative Pathways Plants that fix carbon exclusively through the Calvin
Cycle- C3 Plants
Because of the 3-C compound PGA, that is initiallyformed.
Example: Rice, wheat, oats, and soybeans
-
8/11/2019 Dark Reaction ppt
11/13
Alternative Pathways Plants in hot, dryclimates use alternative pathways
Plant lose H2Oto the air-through small pores calledstomata (underside of leaf)
Can be partially closed to prevent water loss
Stomata are the major passageways through which CO2enters and O2leaves
(when stomata are closed CO2levels decreaseand O2levels increase)
-
8/11/2019 Dark Reaction ppt
12/13
C4 Plants Fix CO4into 4-C
compounds
Partially close stomata
during hottest part of theday
Enzymes fix CO2into 4-Ccompounds and transportthem to cells where CO2isreleased and enters calvincycle ( lose as muchH2O as C3)
Examples Corn, sugar cane, crabgrass
-
8/11/2019 Dark Reaction ppt
13/13
CAM Pathways Open stomata at night;close during the day
Take in CO2at night and
fix into compounds
Release O2during theday and enter the Calvin
cycle
Example: cacti,pineapples