The light independent reactions of photosynthesis

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The light independent reactions of photosynthesis

Introduction You, like all organisms on Earth, are a carbon-based life form. In other words, the complex molecules of your amazing body are built on carbon backbones. Carbon atoms end up in you, and in other life forms, thanks to the second stage of photosynthesis, known as the Calvin cycle or the light-independent reactions.


These reactions are also called the light-independent reactions because they are not directly driven by light. Unlike the light reactions, which take place in the thylakoid membrane, the reactions of the Calvin cycle take place in the stroma the inner space of chloroplasts.

The light independent reactions of photosynthesis

Here is a general diagram of the cycle: Diagram of the Calvin cycle, illustrating how the fixation of three carbon dioxide molecules allows one net G3P molecule to be produced that is, allows one G3P molecule to leave the cycle. This reaction is catalyzed by the enzyme rubisco. One G3P molecule leaves the cycle and will go towards making glucose, while five G3Ps must be recycled to regenerate the RuBP acceptor.

Regeneration involves a complex series of reactions and requires ATP.

1) Carbon dioxide fixation

For every three turns of the Calvin cycle, three atoms of carbon are fixed from three molecules of carbon dioxide. In the carbon fixation stage, carbon dioxide is attached to RuBP by the enzyme rubisco. The resulting 6-carbon product quickly splits into two molecules of a three-carbon compound 3-phosphoglycerate.

When three carbon dioxide molecules enter the cycle, six molecules of 3-phosphoglycerate are produced. In the reduction stage, each 3-phosphoglycerate first gains a phosphate group from an ATP molecule which is converted to ADP.

The net result of this process is conversion of a 3-phosphoglycerate molecule into a molecule of the three-carbon sugar glyceraldehyde 3-phosphate G3P.

Photosynthesis — bozemanscience

For every three turns, one molecule of G3P exits the cycle and goes towards making glucose. Two G3Ps can combine to make one glucose, so one G3P can be thought of as "half" a glucose molecule. The other five G3P molecules are recycled to regenerate three molecules of RuBP, the starting compound of the cycle.

In the regeneration stage, the five G3Ps are reorganized into three five-carbon compounds through a complex series of reactions.Thylakoids contain a variety of pigments (green red, orange, yellow) Chlorophyll (C55H70MgN4O6) is the most common pigment in plants & algae; Chlorophyll a & chlorophyll b are the 2 most common types of chlorophyll in autotrophs.

Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities. This chemical energy is stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water – hence the name photosynthesis, from the Greek φῶς, phōs, "light", and σύνθεσις.

How is ATP produced in cells; what is the difference between the energy-producing process in animal cells and plant cells? How much ATP is produced? This electron loss is repaid from electrons taken from water during the process of photolysis. Photolysis is the splitting of water by light – the basis for non-cyclic photophosphorylation.

This requires a continuous supply of water as a raw material for the process. Which numered label indicates the region where the light-independent reactions take place? These involve the reduction of carbon dioxide using reduced NADP and ATP produced in the light-dependent reactions of photosynthesis.

The reactions are known as the Calvin cycle, and they take place in the stroma of the chloroplast.

The light-independent reactions of photosynthesis