Ashley13111
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Describe the overall changes in matter that occur during the light-independent reactions. What does the plant start with and what does it end with? What is the source of energy that powers this change?

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znk

Answer:

In the light-independent reactions, the plant starts with carbon dioxide and ends up with glyceraldehyde-3-phosphate (G3P). It uses ATP and NADPH from the light-dependent reactions as energy sources  

Explanation:

Step 1: CO₂ adds to ribulose biphosphate (RBP) to form a six-carbon sugar that immediately decomposes into two molecules of 3-phosphopglycerate (3-PGA).

CO₂ + RBP ⟶ 2 3-PGA

Step 2. A phosphate group adds to the 3-PGA to form 1,3-biphosphoglycerate (1,3-BPG).

3-PGA + ATP ⟶ 1,3-BPG + ADP

Step 3. NADPH reduces the 1,3-BPG to G3P

1,3-BPG + NADPH ⟶ G3P + NADP⁺

Most of the G3P is regenerated into RBP, but some leaves the cycle to become glucose.

marianaegarciaperedo

Light-independent reaction uses ATP and NADPH coming from light-dependent reactions. Fixate C from CO₂ molecules to organic molecules (RuBP), and produces G3P. In the cytosol G3P turns into glucose and  fructose.

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Photosynthesis involves two stages: light-dependent and light-independent reactions.

• During light-dependent reactions, oxygen is released, while ATP and NADPH are produced. Both of them are used during light-independent reactions.

• Light-independent reaction is known as the Calvin cycle, and it takes place in the stroma.

• During the Calvin cycle, sugars or carbohydrates are synthesized.

• When carbón dioxide, CO₂, enters the leaves through stomas, it diffuses to the chloroplast stroma.

• Carbon atoms fixate, meaning that they incorporate into organic molecules. These molecules are used to produce 3-C sugars.

• The whole process is impulsed by ATP and NADPH coming from light-dependent reactions.  

Stroma

1. During the carbon fixation phase, a CO₂ molecule combinate with a ribulose-1,5-bisphosphate (5-C molecule) to form 6-C molecules, which will divide into two 3-phosphoglycerate molecules, 3-PGA (3-C molecules).

     CO₂ + ribulose-1,5-bisphosphate ⟶  6-C molecule ⟶ 2  3-PGA

2. During the reduction phase, ATP and NADPH are used to produce the sugar molecule glyceraldehyde-3-phosphate (G3P) from 3-PGA molecules.

         

NADPH donates its electrons to turn 3-PGA into glyceraldehyde 3-phosphate, G3P.

                   3-PGA + ATP + NADPH  ⟶ G3P + ADP + NADP⁺

3. During the regeneration phase,

  • some glyceraldehyde 3-phosphate molecules leave the cycle and go to the cytosol to form glucose.
  • Other G3P get recycled to regenérate the RuBP acceptor. This last reaction needs ATP and a series of other reactions.

When three CO₂ enters the cycle, 6 G3P are produced. One of them leaves the cycle, and the remaining five are recycled and generate three RuBP.

Cytosol:

  • Once in the cytosol, glyceraldehyde 3-phosphate molecules are used to form glucose and  fructose.
  • These two molecules are the monosaccharides that form sucrose.
  • Once sucrose is  formed, it is transported from the photosynthetic tissues to different parts of the plant by the phloem.  

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