What Is the Meaning of Photosynthesis?


Photosynthesis is one of the most important biochemical processes on our planet. It is the process by which green plants and certain other organisms use sunlight, carbon dioxide, and water to produce oxygen and glucose. In this tutorial, we will explore what is photosynthesis, its meaning, stages and importance.


The word "photosynthesis" is derived from the Greek words’ "photo" meaning "light" and "synthesis" meaning "to put together". Therefore, the literal meaning of photosynthesis is "to put together with light". This refers to the process by which plants use the energy from sunlight to synthesize organic compounds from carbon dioxide and water.

Stages of Photosynthesis

Photosynthesis occurs in two stages: the light-dependent reactions and the light-independent reactions. During the light-dependent reactions, which take place in the thylakoid membranes of the chloroplast, light energy is converted into chemical energy in the form of ATP and NADPH. This process involves two photosystems: photosystem I (PSI) and photosystem II (PSII), which work together to produce energy-rich molecules. The process is called the Z scheme because of the shape of the energy graph.

Photosystem II (PSII) is responsible for absorbing light energy, and the energy is used to split water molecules into oxygen and hydrogen ions. These hydrogen ions and electrons are then used to generate ATP through a process called chemiosmosis. Meanwhile, Photosystem I (PSI) use light energy to generate NADPH by accepting electrons and hydrogen ions from the electron transport chain.

The light-independent reactions, also known as the Calvin Cycle, take place in the stroma of the chloroplast. In this stage, carbon dioxide is converted into glucose using the energy stored in ATP and NADPH produced during the light-dependent reactions. The process involves several enzymes and molecules, including Rubisco, which catalyzes the first step of the cycle.

Z Scheme and Photosystems 1 and 2

The Z scheme is a model that explains the movement of electrons through the light-dependent reactions. It is called the Z scheme because the energy graph looks like a Z when plotted. The Z scheme is made up of two photosystems: photosystem I (PSI) and photosystem II (PSII). These photosystems work together to produce ATP and NADPH, which are energy-rich molecules.

Photosystem II (PSII) is the first photosystem in the Z scheme. It absorbs light energy and uses it to split water molecules into oxygen and hydrogen ions. The hydrogen ions and electrons generated by this process are used to create a proton gradient, which is then used to generate ATP through chemiosmosis.

Photosystem I (PSI) is the second photosystem in the Z scheme. It uses light energy to generate NADPH by accepting electrons and hydrogen ions from the electron transport chain. The energy stored in NADPH is used in the Calvin Cycle to convert carbon dioxide into glucose.

Calvin Cycle

The Calvin Cycle, also known as the light-independent reactions, takes place in the stroma of the chloroplast. The process starts with the enzyme Rubisco catalyzing the fixation of carbon dioxide into a molecule called 3-phosphoglycerate. This molecule is then converted into a molecule called glyceraldehyde-3-phosphate (G3P), which is used to produce glucose.

Calvin cycle is a process that occurs in the stroma of chloroplasts, which is the fluid-filled space surrounding the thylakoid membranes. The process begins with the fixation of CO2 molecules into an organic molecule called RuBP (ribulose bisphosphate), which is catalyzed by the enzyme Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase).

After CO2 fixation, the resulting molecule is quickly broken down into two molecules of 3-phosphoglycerate (3-PGA). This reaction requires energy in the form of ATP and electrons in the form of NADPH, which were produced during the light-dependent reactions. The energy and electrons are used to reduce the 3-PGA molecules into G3P (glyceraldehyde-3-phosphate), which is a three-carbon sugar.

Most of the G3P molecules produced during the Calvin cycle are used to regenerate RuBP, which is necessary to continue the cycle. However, some of the G3P molecules are used to synthesize glucose and other organic compounds, which can be stored or used by the plant for energy.

Importance of Photosynthesis

Photosynthesis is essential for life on Earth. It is the primary source of energy for most living organisms.

Production of Oxygen

Photosynthesis is responsible for the production of oxygen in the atmosphere. The oxygen that is produced during photosynthesis is used by all aerobic organisms, including humans, for respiration. Without photosynthesis, there would be no oxygen in the atmosphere, and life as we know it would not be possible.

Food Production

Photosynthesis is the primary source of food for all living organisms. Plants produce carbohydrates and other organic compounds through photosynthesis, which are used as a source of energy by all animals. Humans also rely on photosynthesis indirectly for food, as most of our food comes from plants or from animals that feed on plants.

Carbon Dioxide Removal

Photosynthesis is responsible for removing carbon dioxide from the atmosphere. Carbon dioxide is a greenhouse gas that contributes to global warming. Photosynthesis helps to regulate the amount of carbon dioxide in the atmosphere and prevent the negative impacts of global warming.

Soil Conservation

Plants that carry out photosynthesis help to prevent soil erosion. Their roots hold the soil in place and prevent it from washing away during heavy rains. This helps to maintain soil fertility and prevent land degradation.

Economic Importance

Photosynthesis has significant economic importance as it is the basis of agriculture and forestry. Plants are the primary source of raw materials for many industries, including textiles, paper, and construction. Photosynthesis also contributes to the production of biofuels, which are an important source of renewable energy.


Photosynthesis supports biodiversity by providing habitats and food for many species of plants and animals. Without photosynthesis, many species of plants and animals would go extinct, leading to a decline in biodiversity.

Ecological Balance

Photosynthesis helps to maintain ecological balance by regulating the carbon cycle. Carbon is a vital element for all living organisms, and photosynthesis helps to regulate the amount of carbon in the atmosphere and in the soil.


In conclusion, photosynthesis is a complex process that is essential for life on Earth. The light-dependent reactions convert light energy into chemical energy, which is then used to power the Calvin cycle. The Calvin cycle uses the chemical energy to convert CO2 into organic compounds, which are necessary for plant growth and survival. Understanding the intricacies of photosynthesis is essential for improving crop yields, mitigating the effects of climate change, and developing sustainable energy sources for the future.


Q1: What are the products of photosynthesis?

Ans: Photosynthesis produces two main products: oxygen and glucose. Oxygen is released as a byproduct of the process, while glucose is used by the plant as an energy source and also serves as a building block for more complex organic molecules.

Q2: What is the role of chlorophyll in photosynthesis?

Ans: Chlorophyll is a pigment molecule that absorbs light energy from the sun and transfers it to other molecules within the plant cell. It is the primary pigment involved in photosynthesis and gives plants their green color. Chlorophyll is essential for capturing the energy needed to drive the process of photosynthesis.

Q3: How does photosynthesis benefit the environment?

Ans: Photosynthesis is essential for life on Earth, as it provides oxygen for us to breathe and serves as the basis for most food chains.

Updated on: 19-Apr-2023


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