What is Photosynthesis?

Plants have a capacity that we humans can only imagine— the ability to produce food from sunlight. Sure, we can prepare some dishes that we can savor on, but it become possible because of the plants (as they serve as a producers of all the raw materials required). Photosynthesis is the method of assembling carbohydrates with the aid of sunlight.

Keep in mind that the sun emits a wide range of energy, including heat and gamma rays, but photosynthesis captures only light energy. In addition, photosynthesis produces glucose, a simple sugar molecule that can be used to make more complex carbohydrates.

Photosynthesis in Various Organisms:

"Photosynthesis in various organisms"

The prefix 'photo' means light, and 'synthesis' means to bring together. Photosynthesis is a process that occurs in species other than green plants. Several prokaryotes, such as cyanobacteria, purple and green sulfur bacteria, are among them. Photosynthesis is present in these species, just as it is in green plants.

Photosynthesis produces glucose, which is then used to power various cellular functions. This physio-chemical process produces oxygen as a by-product.

Algae uses photosynthesis to turn solar energy into chemical energy. As a byproduct, oxygen is produced, and light is an important factor in completing the photosynthesis process.

Plants use light energy to turn carbon dioxide and water into glucose and oxygen during photosynthesis. Chloroplasts are microscopic cellular organelles found in leaves.

Chlorophyll, a green pigment, is used in every chloroplast. Chlorophyll molecules absorb light energy, while carbon dioxide and oxygen enter through the tiny pores of stomata in the epidermis of leaves.

Sugars including glucose and fructose are another by-product of photosynthesis.

These sugars are then transported to the roots, branches, leaves, fruits, flowers, and seeds of the plant. In other words, the plants use these sugars as a source of energy, which aids their development. More complex carbohydrates, such as cellulose and starch, are formed when these sugar molecules combine. Plant cell walls are made up of cellulose, which serves as a structural material.

Where does Photosynthesis Occur?

"Site of occurrence of photosynthesis"

Photosynthesis takes place in chloroplasts, which are found in plants and blue-green algae. Chloroplasts are green color plastids are found in all green parts of a plant, including the green roots, green leaves, and sepals – floral parts. Only plant cells have these cell organelles, which are found in the mesophyll cells of leaves.

An Overall Reaction of Photosynthesis

" Overall reaction of Photosynthesis"

Carbon dioxide and water are the two reactants in the photosynthesis reaction. Two products are generated by these two reactants: oxygen and glucose. As a result, photosynthesis is classified as an endothermic reaction. The photosynthesis formula is as follows:

Unlike plants, bacteria that conduct photosynthesis do not produce oxygen as a by-product of their work. Anoxygenic photosynthetic bacteria are bacteria that do not produce oxygen. Oxygenic photosynthetic bacteria are those that produce oxygen as a by-product of photosynthesis.


Chlorophyll is a green pigment present in the chloroplasts of plants and cyanobacteria's mesosomes. By allowing plants to absorb energy from sunlight, this green pigment plays an important role in the photosynthesis process. Chlorophyll is made up of two types of chlorophyll: chlorophyll a and chlorophyll b.

Other species that conduct photosynthesis produce different types of chlorophyll, such as chlorophyll-c1, chlorophyll-c2, chlorophyll-d, and chlorophyll-f, in addition to green plants.

The Process of Photosynthesis

The photosynthesis process takes place in cell organelles called chloroplasts at the cellular level. Chlorophyll, a green pigment found in these organelles, is responsible for the leaves' distinctive green color.

As previously mentioned, photosynthesis takes place in the leaves, and the chloroplast is the specialized cell organelle responsible for this process. A leaf is made up of three parts: a petiole, an epidermis, and a lamina. During photosynthesis, the lamina is used to absorb sunlight and carbon dioxide.

Steps Involved in Photosynthesis

Carbon dioxide enters via the stomata, and water is absorbed from the soil by the root hairs and carried to the leaves by the xylem vessels during photosynthesis. The sun's light energy is absorbed by chlorophyll, which splits water molecules into hydrogen and oxygen.

Glucose is made from hydrogen derived from water molecules and carbon dioxide absorbed from the air. Furthermore, as a waste product, oxygen is released into the atmosphere through the leaves.

Plants use glucose as a source of energy for growth and development, with the remainder being retained in the roots, leaves, and fruits for later use.

Other essential cellular components of photosynthesis are pigments. They are the molecules that give color to things, and they absorb light of a certain wavelength and reflect the rest back. Chlorophyll a, chlorophyll b, and carotenoids are included in the thylakoids of chloroplasts in all green plants. Its primary function is to collect light energy. The primary pigment is chlorophyll-a.

The Process of Photosynthesis Occurs in Two Stages

  1. Light-dependent reaction or light reaction
  2. Light independent reaction or dark reaction

Light reaction:

The light reaction, which occurs only during the day in the presence of sunlight, is the first step in photosynthesis. The light-dependent reaction occurs in the thylakoid membranes of chloroplasts in plants.

Photosystems are membrane-bound sacs like structures found within the thylakoid that act by gathering light.

Large complexes of pigment and protein molecules are present within the plant cells, and these photosystems play a key role in the photosynthesis light reactions.

Photosystems are divided into two categories: photosystem I and photosystem II.

The light energy is converted to ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) in light-dependent reactions, which are used in the second step of photosynthesis.

Two electron-transport chains produce ATP and NADPH, water is consumed, and oxygen is released during the light reactions.

The chemical equation in the light reaction of photosynthesis can be reduced to: 2H2O + 2NADP+ + 3ADP + 3Pi → O2 + 2NADPH + 3ATP

Dark reaction:

Carbon-fixing reaction is another name for dark reaction.

Sugar molecules are created from water and carbon dioxide molecules in a light-independent phase.

The dark reaction takes place in the stroma of the chloroplast, where the light reaction's NADPH and ATP products are used.

Via stomata, plants absorb carbon dioxide from the atmosphere and enter the Calvin photosynthesis cycle.

ATP and NADPH produced during the light reaction drive the Calvin cycle, which converts six molecules of carbon dioxide into one sugar molecule, or glucose.

The chemical equation for the dark reaction can be reduced to:

3CO2 + 6 NADPH + 5H2O + 9ATP → G3P + 2H+ + 6 NADP+ + 9 ADP + 8 Pi

Importance of Photosynthesis

Photosynthesis is needed for all life on Earth to survive. It plays an important role in the food chain because it is through this mechanism that plants make their food, forming the primary producers.

Photosynthesis is also responsible for the production of oxygen, which is needed for the survival of most organisms.

Context and Applications:

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for;

  • Bachelors in Sciences (Botany)
  • Masters in Sciences (Botany)
  • Masters in Technology (Biotechnology)

Want more help with your biology homework?

We've got you covered with step-by-step solutions to millions of textbook problems, subject matter experts on standby 24/7 when you're stumped, and more.
Check out a sample biology Q&A solution here!

*Response times may vary by subject and question complexity. Median response time is 34 minutes for paid subscribers and may be longer for promotional offers.

Search. Solve. Succeed!

Study smarter access to millions of step-by step textbook solutions, our Q&A library, and AI powered Math Solver. Plus, you get 30 questions to ask an expert each month.

Tagged in


Plant physiology and Biochemistry

Photosynthesis & Respiration

Photosynthesis Homework Questions from Fellow Students

Browse our recently answered Photosynthesis homework questions.

Search. Solve. Succeed!

Study smarter access to millions of step-by step textbook solutions, our Q&A library, and AI powered Math Solver. Plus, you get 30 questions to ask an expert each month.

Tagged in


Plant physiology and Biochemistry

Photosynthesis & Respiration