What is Photosynthesis? | Types, Definition, Structure, Function & Facts

What is Photosynthesis?

Have you ever noticed that plants need sunlight to live? Sounds a bit strange right? How can sunlight be a food? Well, sunlight is energy and photosynthesis is the process plants use to get energy from sunlight and use it to convert carbon dioxide and water into food.

Three things plants need to live

Plants need three basic things to live: water, sunlight, and carbon dioxide. Plants breathe carbon dioxide just like we breathe oxygen. When plants inhale carbon dioxide, they exhale oxygen. Plants are the main source of oxygen on planet Earth and help us sustain life.

We now know that plants use sunlight for energy, they get water from rain, and they take in carbon dioxide by breathing. The process of taking these three main ingredients and turning them into food is called photosynthesis.

How do Plants Capture Sunlight?

Plants absorb sunlight using a compound called chlorophyll. Chlorophyll is green, which is why so many plants are green. At first you might think it is green because it wants to absorb and use green light. However, from the study of light, we know that the color we see is actually the color of the reflected light. Thus, chlorophyll reflects blue light and absorbs blue and red light.

More details on Photosynthesis

Inside the cells of plants are structures called chloroplasts. It is in these structures that chlorophyll resides.

There are two main stages in photosynthesis. In the first stage, sunlight is absorbed by chloroplasts and the energy is stored in a chemical called ATP. In the second stage, ATP is used to make sugars and organic compounds. These are the foods that plants use to live and grow.

The first stage of the process must have sunlight, but the second stage can happen when there is no sunlight and even at night. The second stage is called the Calvin cycle because it was discovered and described by scientist Melvin Calvin.

Although plants need sunlight and water to live, different plants need different amounts. Some plants need a little water while others need a lot. Some plants prefer full sun, while others prefer shade. Knowing more about your plants’ needs can help you figure out where to plant them in your garden and how to best water them so they thrive.


We now know that plants need sunlight, water, and carbon dioxide to live. They take these three ingredients and use chlorophyll to help convert them into food that they use for energy and the oxygen they breathe out and which we use to live. All plants use photosynthesis, so they all need sunlight.

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