Dark Reaction ppt

8/11/2019 Dark Reaction ppt

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By: ANAZ. ANATURAL SCIENCE

Candidate

code:13375006


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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


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STEP 1An enzyme (rubisco),

combines CO2with a 5-carbon sugar RuBP

The product, 6-C sugar,immediately splits into

2, -3C molecules (PGA)

PGAPhosphoglycericAcid


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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)


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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


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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)


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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.


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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


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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)


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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


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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

Documents

Dark Reaction ppt