When animals are hungry, they need to find and eat food, but for plants, which cannot move, the only nutrition available is the minerals they can draw from the soil. However, unlike animals, plants can make their own food using a process called photosynthesis.

What Is Photosynthesis?

Photosynthesis is a process in which organisms convert light energy from sunlight into chemical energy. The purpose of photosynthesis is to provide organisms with energy to sustain their metabolic processes. Photosynthesis is most commonly found in plants and algae but can also be observed in some bacteria. The process of photosynthesis is critically important for all life on earth: Plants need photosynthesis to survive, herbivores need plants to survive, and carnivores need herbivores to survive.

How Does Photosynthesis Work?

Three main ingredients are required for photosynthesis: water, carbon dioxide, and light. Plants use light energy from the sun to convert six water molecules (6 H2O) and six carbon dioxide molecules (6 CO2) into a molecule of glucose and six molecules of oxygen. This process occurs within cellular structures called chloroplasts. The sequence can be divided into two phases: light-dependent reactions and light-independent reactions. The light-dependent reactions involve pigments called chlorophylls, which absorb light energy and use it to produce two molecules: ATP and NADPH. These two molecules are then used in a light-independent reaction known as the Calvin cycle. In the Calvin cycle, APT and NADPD provide energy for a chemical reaction that converts carbon dioxide into sugar.

Photosynthesis Facts

From a biological standpoint, photosynthesis is the most important process on Earth. It's the battery that powers life as we know it. In fact, photosynthesis provides more than 99% of the energy that sustains life on Earth. The history of this pivotal process dates back billions of years: The first photosynthetic bacteria appeared on Earth more than 3.4 billion years ago. However, photosynthesis was very different back then. Rather than using visible light, ancient bacteria absorbed near-infrared light. They also produced sulfur as a byproduct, rather than oxygen. The first oxygen-producing bacteria, called cyanobacteria, didn't come for another 700 million years. Land plants, which descended from green algae, came on the scene around 450 million years ago and have evolved into all of the plant species we see today. Every breath we take contains oxygen that was produced by these plants.

All About Chloroplasts

Chloroplasts can be thought of as tiny "energy factories" within plant and algae cells. They exist inside the fluid of a cell and are responsible for the process of photosynthesis. Chloroplasts are enveloped by a double membrane. Within these membranes is a gelatinous space called the stroma. Thykaloids are structures found in the stroma that contain chlorophyll. Chlorophyll is essential for photosynthesis: It's the green pigment that absorbs light energy from the sun. When chlorophyll absorbs light energy, it emits electrons and propels hydrogen ions through the thykaloid membrane. This drives the production of ATP molecules within the stroma, and these ATP molecules serve as the energy source to power the Calvin cycle.

Energy, Oxygen, and Light/Dark Reactions

At its core, photosynthesis is all about the conversion of energy. Our sun radiates a massive amount of energy, but this energy needs to be converted to a different form before it can be used by organisms. The two phases of photosynthesis can be referred to as light and dark reactions. The first phase is referred to as a light reaction because it involves the absorption of light energy from the sun. This light energy is then converted to chemical energy in the form of ATP and NADPH. The second phase, known as the Calvin cycle, can be considered a dark reaction because it does not require light energy. Rather, the chemical energy stored as ATP and NADPH fuels a reaction that ultimately yields carbohydrates from carbon dioxide molecules. An important aspect of this process is that it produces oxygen as a byproduct. Without photosynthesis, there'd be no oxygen for humans to breathe.

Learn More About Photosynthesis