Calvin cycle

Plants make food in a special way.

They take in air to make food. This happens in the green parts of the leaf. The plant uses energy from the sun to do this.

This process is like a cycle that keeps going. It makes tiny bits of food for the plant. The plant uses this food to grow. It is a very busy job for a leaf!

Plants make food through a set of steps called the Calvin cycle.

This cycle happens in the stroma. The stroma is a fluid part inside the chloroplast. This is where the plant turns gas into sugar.

First, the plant takes in carbon dioxide from the air. An enzyme called RuBisCO helps this happen. This step is called carboxylation. Next, the plant uses power from the light reactions. It uses two things called ATP and NADPH. These give the power needed to make sugar.

The cycle makes a three-carbon sugar called G3P. The plant does not make glucose right away. It must use G3P to build larger sugars later. To keep the cycle going, the plant must also reset. This third stage is called regeneration. It uses more ATP to remake the starting parts.

Some people call this the "dark reaction." But this name is not quite right. The cycle needs NADPH from the light reactions. Since NADPH does not last long, the cycle needs light too. It works best when the sun is out.

The Calvin cycle is a very important way that living things make food.

It is a series of chemical reactions that turn carbon dioxide into sugar. This process is often called carbon fixation. It happens in all photosynthetic eukaryotes and many types of bacteria. In plants, these reactions take place in the stroma. The stroma is the fluid part inside a chloroplast.

This cycle helps provide energy for the plant and for animals that eat it.

The cycle works in three main steps. First is carboxylation, where carbon dioxide is added to a molecule called RuBP. An enzyme named RuBisCO helps this happen.

Next is the reduction stage. The plant uses stored energy from ATP and NADPH to change the molecules. This creates a three-carbon sugar called G3P. The final step is regeneration. The plant uses more ATP to turn G3P back into RuBP. This resets the cycle so it can start again.

Scientists discovered this cycle in 1950. Melvin Calvin, James Bassham, and Andrew Benson found it. They worked at the University of California, Berkeley. They used a special radioactive isotope called carbon-14 to see the reactions. This helped them map out how the molecules move and change. Their work showed us how plants build their own bodies from thin air.

There are many specific facts about how this cycle runs. To make one G3P molecule, the cycle needs three turns. To make one glucose molecule, the plant needs six turns.

The cycle uses nine ATP and six NADPH molecules for every three turns. It produces G3P, which has three carbons. The cycle is sometimes called the "dark reaction." However, this name is a bit misleading. The cycle needs NADPH, which comes from light-dependent reactions. Because NADPH does not last long, the cycle needs light to work.

You can think of the Calvin cycle like a factory assembly line. The carbon dioxide is the raw material coming in. The ATP and NADPH are the electricity that runs the machines.

Even though the machines do not need direct sunlight, they need the electricity from the solar panels. Without the sun to make the electricity, the factory would quickly run out of power. This is why the cycle works best when light is available.

The Calvin cycle is a vital series of chemical reactions used by photosynthetic organisms. It is often called carbon fixation because it turns inorganic carbon dioxide into organic compounds. These compounds, such as sugars, provide energy for the plant and the animals that eat it.

This cycle occurs in all photosynthetic eukaryotes and many photosynthetic bacteria. In plants, these reactions take place in the stroma. The stroma is the fluid-filled region inside a chloroplast, located outside the thylakoid membranes.

The cycle functions through a sequence of reduction-oxidation, or redox, reactions. It does not convert molecules into sugar in one single step. Instead, it uses a step-wise process to build complex molecules. The cycle relies on two specific products from the light-dependent reactions: ATP and NADPH. ATP provides chemical energy, while NADPH provides reducing power. These substrates drive the transformation of carbon dioxide into three-carbon sugar molecules.

Scientists divide the Calvin cycle into three distinct functional stages. The first stage is carboxylation. During this phase, the enzyme RuBisCO catalyzes the addition of carbon dioxide to a five-carbon molecule called ribulose 1,5-bisphosphate, or RuBP. This creates an unstable six-carbon compound that immediately splits. The second stage is the reduction reaction. Here, the molecules are modified using ATP and NADPH to produce glyceraldehyde-3-phosphate, known as G3P. The third stage is RuBP regeneration. This stage uses more ATP to rearrange G3P molecules back into RuBP so the cycle can continue.

In 1950, researchers discovered the specific mechanics of this cycle. Melvin Calvin, James Bassham, and Andrew Benson conducted their work at the University of California, Berkeley. They used a radioactive isotope called carbon-14 to track the movement of carbon atoms. This method allowed them to map the complex biochemical pathways of the cycle. Their discovery provided a clear view of how plants build organic matter from carbon dioxide.

The mathematical precision of the cycle is quite remarkable. To produce one net molecule of G3P, the cycle must turn three times. This process requires exactly nine molecules of ATP and six molecules of NADPH. Because G3P is a three-carbon sugar, it takes six turns of the cycle to produce one six-carbon glucose molecule.

While many texts focus on glucose, the immediate carbohydrate products are actually triose phosphates like G3P. Plants can then use this surplus G3P to create starch, sucrose, or cellulose depending on their needs.

It is a common misconception that the Calvin cycle occurs only in the dark. While it is sometimes called the "dark reaction," it actually requires light to function. This is because the cycle depends on NADPH, which is a short-lived molecule. NADPH is produced during the light-dependent reactions and is used up quickly. If there is no light, the plant must rely on starch reserves to provide energy. Furthermore, the enzymes in the cycle are often activated by light or by the products of light-dependent reactions. This regulation prevents the plant from wasting energy when it cannot produce new sugars.

The Calvin cycle is also closely connected to other biological processes. One such connection is photorespiration, also known as the C2 cycle. This occurs when the RuBisCO enzyme reacts with oxygen instead of carbon dioxide. Photorespiration can be a negative consequence for the plant because it leads to a loss of carbon. Some plants, like corn, have evolved C4 carbon fixation to help circumvent this problem. Other plants, known as CAM plants, use a different method by storing malic acid at night to make the cycle work during the day.