What Is Energy From Light Called?

Energy from light refers to the process by which plants, some bacteria, and some protistans convert sunlight into chemical energy that can be used to fuel the organism’s activities. This process is called photosynthesis. Photosynthesis is essential for all aerobic life on Earth as it provides the primary source of energy and oxygen in the atmosphere. In 1845 Jan Ingenhousz wrote about experiments that showed how sunlight played a pivotal role in facilitating plant growth. Today, we know that photosynthesis acts as a bridge between light energy and chemical energy by converting solar energy into carbohydrates.

Photosynthesis is a complex process that can be divided into two main stages—the light dependent reactions and the Calvin cycle. In the light dependent reactions, energy from sunlight is absorbed by chlorophyll and converted into chemical energy stored in ATP and NADPH. In the Calvin cycle, carbon dioxide and water are converted into organic compounds like glucose by utilizing the ATP and NADPH generated from the light dependent reactions. The glucose can then be used by plants, algae and cyanobacteria as an energy source to grow and reproduce.

By harnessing the power of sunlight to produce carbohydrates, photosynthesis provides the foundation for sustaining most life on Earth. Understanding the intricate details of how photosynthesis works has also opened doors to bioengineering projects that aim to enhance crop yields or increase carbon dioxide processing, helping combat food scarcity and climate change.

History of Discovering Photosynthesis

The discovery of photosynthesis was a long process involving many scientists across several centuries. Some of the key events and figures in the history of photosynthesis research include:

In the 1770s, scientist Joseph Priestley performed experiments that demonstrated plants refresh the air and allow candles to burn longer in an enclosed space with plants. This laid early groundwork for discovering the role of plants in processing air.

In 1779, Dutch physician Jan Ingenhousz expanded on Priestley’s work. He showed that the process renewing the air required sunlight and only occurred in the green parts of plants. This identified photosynthesis as the key plant process behind purifying air.

In the early 1800s, researchers discovered that plants absorb carbon dioxide and release oxygen. This established the basic gas exchange of photosynthesis.

In 1845, German chemist Julius von Mayer described plants transforming light into chemical energy. This discovery of light as the energy source for plant processes helped establish modern photosynthesis research.

Over many decades, scientists continued unraveling the complex biochemistry of photosynthesis. Key milestones included identifying chlorophyll, understanding photosystems, finding the Calvin cycle reactions, and mapping the light-dependent and light-independent stages we recognize today.

How Photosynthesis Works

Photosynthesis is a complex process that can be divided into two main stages: light reactions and dark reactions. Here’s an overview of what happens during each stage:

Light Reactions

The light reactions take place in the thylakoid membranes within chloroplasts. This is where chlorophyll and other pigments absorb light energy. The light energy is used to split water molecules, releasing oxygen as a waste product. This light reaction also generates ATP and NADPH, which provide the energy and electrons needed for the dark reactions.

Dark Reactions

The dark reactions, also known as the Calvin cycle, take place in the stroma of the chloroplasts. This is where carbon dioxide from the air is fixed into glucose molecules. The ATP and NADPH produced during the light reactions provide the necessary energy and electrons for this process. The end result is carbohydrates like glucose.


Through these light and dark reactions, photosynthesis is able to harness light energy to convert carbon dioxide and water into glucose and oxygen. The glucose provides food for plants, while the oxygen is released into the atmosphere where it is used by other organisms for cellular respiration.

The Photosystems

Photosynthesis involves two main photosystems that absorb light energy and use it to drive the synthesis of organic compounds. These two photosystems are Photosystem I and Photosystem II.

Photosystem II is present in the thylakoid membrane of plants, algae and cyanobacteria. When a photon of light hits Photosystem II, it excites electrons from a chlorophyll molecule. These energized electrons are captured and used to split water molecules, releasing oxygen as a byproduct of photosynthesis.

Photosystem I contains a chlorophyll molecule that can absorb a different wavelength of light than Photosystem II. When Photosystem I absorbs light energy, it energizes electrons that are then passed along an electron transport chain. The electron transport chain moves the electrons, using their energy to pump hydrogen ions into the thylakoid space.

Both photosystems contain light-harvesting complexes made up of proteins and chlorophyll molecules. These complexes help absorb additional light energy and transfer it to the chlorophyll molecules in the photosystem reaction center. The two photosystems work together in the light reactions of photosynthesis to convert light energy into chemical energy.

Light Absorption Process

The light absorption process of photosynthesis starts when light energy is captured by pigments such as chlorophyll. Located in the thylakoid membranes of chloroplasts, chlorophyll gives leaves their green color and absorbs blue and red light from the visible light spectrum. Accessory pigments such as carotenoids absorb other wavelengths of light that chlorophyll cannot capture, allowing plants to make use of a wider range of available light.

When a pigment molecule absorbs a photon of light, an electron in the molecule becomes excited to a higher energy state. The excited electron is unstable and wants to return to its ground state quickly. This initial stage of photosynthesis produces excited electrons that can be harnessed to power the rest of the process.

Chlorophyll a is the primary pigment that absorbs light and provides energy for photosynthesis. Other important pigments are chlorophyll b, xanthophylls, and carotenoids like beta-carotene. Each accessory pigment can only absorb a limited band of light wavelengths. By working together, all the pigments can absorb light over a wider range, increasing the efficiency of photosynthesis.

The Calvin Cycle

The Calvin cycle is the second stage of photosynthesis, where the energy from light is used to fix carbon from carbon dioxide into carbohydrates like glucose. This process was discovered by Melvin Calvin and is named after him. The Calvin cycle takes place in the stroma of the chloroplast.
the calvin cycle fixes carbon dioxide into carbohydrates.

The most important step in the Calvin cycle is carbon fixation, which incorporates inorganic carbon from carbon dioxide into organic molecules. This reaction is catalyzed by the enzyme Rubisco, which grabs CO2 from the air and attaches it to a five-carbon sugar called RuBP. This first stable product of carbon fixation is a six-carbon molecule called 3-phosphoglycerate (also known as 3-PGA).

Rubisco is the most abundant protein on Earth and is responsible for basically all of the carbon fixation on the planet. It provides organisms with the carbon backbone needed to build sugars, proteins, cells, and plants. However, Rubisco is not a very efficient enzyme and can react with oxygen as well as carbon dioxide, leading to a process called photorespiration that decreases photosynthetic output. Scientists are researching how to engineer a more efficient Rubisco enzyme to potentially increase crop yields.

Products of Photosynthesis

The process of photosynthesis produces four main products: oxygen, glucose, ATP, and NADPH. These molecules are vital for life as we know it.

The most familiar product is oxygen. Photosynthesis takes in carbon dioxide and water and produces oxygen as a byproduct. Oxygen is released into the atmosphere and is harvested by organisms like animals, fungi and plants to power cellular respiration. The oxygen in our atmosphere originally came from the photosynthesis carried out by ancient cyanobacteria.

Glucose is also a critically important product of photosynthesis. Glucose is a simple sugar that is used by cells as an energy source. The energy in glucose molecules comes from the energy of sunlight that was captured and stored by photosynthesis. Glucose can be broken down through cellular respiration to release that stored energy.

Two other vital molecules produced by photosynthesis are ATP and NADPH. ATP is the cellular energy currency used to power metabolic processes. NADPH is an electron carrier molecule used to drive redox reactions in cells. Both ATP and NADPH provide the chemical energy that allows non-photosynthetic organisms like animals to thrive and survive.

Without photosynthesis producing oxygen, glucose, ATP and NADPH, ecosystems as we know them could not exist. The products of photosynthesis literally energize the planet.

Photosynthesis in Different Organisms

Photosynthesis is carried out by many different organisms, with the most well-known being plants. Plants, algae, and some bacteria are able to perform photosynthesis by using sunlight, water, and carbon dioxide to produce energy-rich molecules like glucose.

In plants, photosynthesis takes place primarily in the leaves, which contain specialized cell structures called chloroplasts. The chloroplasts contain the green pigment chlorophyll, which captures light energy. This energy is used to power the reactions that convert carbon dioxide and water into glucose and oxygen.

Algae are aquatic organisms that contain chloroplasts and perform photosynthesis similar to plants. Algae can be unicellular or multicellular and live in both freshwater and marine environments. There are many different types of algae, including green algae, brown algae, and red algae.

Some bacteria, such as cyanobacteria, are also capable of photosynthesis. Cyanobacteria are ancient organisms that originated oxygen-producing photosynthesis long before plants existed on Earth. They contain chlorophyll and convert sunlight into energy through photosynthesis like plants and algae.

Photosynthesis evolved in these various organisms as a means of harnessing the energy of sunlight to produce the carbohydrates and oxygen needed for life. While the process differs in its details, the ability to capture light energy and convert it into chemical energy is the essential function of photosynthesis in all photosynthetic organisms.

Importance of Photosynthesis

Photosynthesis is arguably the most important biochemical process on Earth. Here are two of the main reasons why photosynthesis is so vital:

Food Production

Photosynthesis enables plants to convert sunlight into chemical energy that they can use to grow and produce food. This food production directly sustains human life and all animal life on the planet since the food they eat relies on photosynthetic plants and organisms. Without photosynthesis, the complex food chains and webs that support nearly all life on Earth would collapse.

Oxygen Generation

One of the byproducts of photosynthesis is oxygen. Photosynthetic organisms release oxygen into the atmosphere, generating and replenishing the Earth’s oxygen supply. The oxygen produced through photosynthesis is essential for most living organisms on Earth, including humans, to breathe. Without photosynthetic oxygen production, life as we know it could not exist.

Recent Photosynthesis Research

Scientists continue to study photosynthesis in hopes of improving it to meet the world’s growing food and energy needs. Some key areas of recent research include:

Improving crop yields: By better understanding photosynthesis, researchers aim to improve the efficiency of food crops like rice, wheat, corn, and soybeans. Projects like C4 Rice and C4 photosynthesis aim to add features from plants like corn into rice to allow it to fix carbon more efficiently. This could significantly increase rice yields.

Bioenergy and biofuels: Algae and cyanobacteria are being engineered for increased photosynthetic efficiency to produce biomass and fuels. Attempts to improve the natural process of photosynthesis could lead to sustainable energy solutions.

Solar energy conversion: Scientists are studying natural photosynthesis to find inspiration for better solar panels. For example, learning from the photon absorption process in plants could improve manufactured solar cells.

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