Plants need energy to live. They use a process called photosynthesis. There are two parts in photosynthesis. In the first part of photosynthesis, plants use sunlight to make energy. The second part is called the Calvin cycle.

In the Calvin cycle, plants grab carbon dioxide (CO₂) from the air. CO₂ is a type of gas. Human beings breathe it out, while plants breathe it in. After taking in CO₂, the plant transforms it. To do this, it uses the energy from the sun. In the end, the plant creates sugar. It uses the sugar as food.

Plants need the Calvin cycle to survive. Many animals, like deer, need to eat plants. Other animals, like wolves, eat other animals. In a way, life exists thanks to the Calvin cycle.

For hundreds of years, scientists knew about photosynthesis. They did not know exactly how it worked, though. Dr. Melvin Calvin was the scientist who figured it out. Because of his discovery, Calvin won the Nobel Prize for chemistry in 1961. It is the highest prize in science.

Steps in the Calvin Cycle
To create sugar, the plant needs to create chemical reactions. It needs energy to start these reactions. Plants get this energy from two chemicals. The chemicals are called ATP and NADPH. These chemicals store energy from sunlight. The energy is used to power the Calvin cycle.

The Calvin cycle has four main steps. In step one, a plant takes CO₂ from the air. It takes a carbon molecule from the CO₂.

Molecules are tiny parts of a chemical. In a chemical reaction, molecules join or split to form new molecules. Carbon dioxide is one example. It is made of carbon and oxygen molecules.

In the Calvin cycle, the carbon from CO₂ joins another molecule. This other molecule is called ribulose biphosphate (RuBP). The new molecule then splits apart. It splits into two molecules called 3-phosphoglycerate (3-PGA).

In step two, the plant changes the 3-PGA into another chemical. The new chemical is called G3P. It is also called glyceraldehyde-3-phosphate.

In step three, some of the G3P molecules are used to make glucose, or sugar.

In step four, the G3P molecules that are left join together. They form RuBP again. The cycle goes back to step one and starts over.

Understanding the Calvin Cycle
The Calvin cycle has inspired new inventions. It helped people learn how to use the sun to make solar power.

One invention that creates solar power is called a photovoltaic cell. This is a machine that uses sunlight to make electricity. Photovoltaic cells are often grouped together to form large solar panels. Solar panels create electrical energy for buildings.

Understanding photosynthesis can help us in other ways too. Right now, Earth is heating up. Scientists say this is because of the fuel people use. Burning fuel like gasoline creates greenhouse gases. These gases trap the heat in the air, causing global warming. CO₂ is a greenhouse gas.

Scientists are studying ways to limit the amount of CO₂. For example, plants could grab more CO₂ from the air. This could slow global warming.