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Photosynthesis: Definition, Meaning, Formula, Process, Diagram, Process

Photosynthesis: Definition, Meaning, Formula, Process, Diagram, Process

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:56 PM IST

Photosynthesis is the process by which green plants, and some other organisms as well, convert light energy into chemical energy. Such chemical energy produces glucose in addition to releasing oxygen. This is an important process that happens in chloroplasts mostly through light-dependent reactions and light-independent reactions. Photosynthesis is the fundamental source of energy for almost all ecosystems. This topic is from the Class 11 chapter Photosynthesis in Higher Plants. It is important for competitive exams such as NEET, and AIIMS BSc Nursing where Biology is one of the main subjects asked.

This Story also Contains
  1. What is Photosynthesis?
  2. Photosynthesis Reaction
  3. Photosynthetic Pigments
  4. Stages of Photosynthesis
  5. Factors Affecting Photosynthesis
  6. C3, C4, And CAM Pathways
  7. Importance of Photosynthesis
  8. Recommended Video on 'Photosynthesis'
Photosynthesis: Definition, Meaning, Formula, Process, Diagram, Process
Photosynthesis: Definition, Meaning, Formula, Process, Diagram, Process

What is Photosynthesis?

Photosynthesis is the biochemical process by which green plants, some algae, and some bacteria convert light energy to chemical energy in organic compounds, mainly glucose. The process involves capturing light energy by such organisms using chlorophyll, changing carbon dioxide and water into glucose and oxygen. All this transformation keeps the plants alive and generates power for other living organisms through the food chain.

Photosynthesis is essential for life on Earth. It is the most significant source of biomolecules for almost all living organisms, sitting at the basis of the food chain. The oxygen that is evolved as a byproduct of photosynthesis is required for the respiration of most living organisms, including human beings. Photosynthesis also plays a very important role in controlling atmospheric carbon dioxide levels and thus, in regulating the Earth's climate.

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Photosynthesis Reaction

Photosynthesis is the process where green plants, algae, and some bacteria capture the energy of sunlight and turn it into chemical energy.

Photosynthesis may be represented by the general equation:

6 CO2 + 6 H2O + light energy → C6H

Historically, scientists like Jan Ingenhousz and Joseph Priestley contributed a lot towards the elucidation of photosynthesis, its basic principles and its requirement for light.

Given below is the photosynthesis diagram:

Photosynthesis Process

Structure of Chloroplasts

Chloroplasts are present in plant cells, responsible for photosynthesis consequently have a highly specialised structure. The principal parts or structures include:

  • Thylakoids: Membrane-bound compartment with light-dependent reactions.

  • Grana: Stack of thylakoids.

  • Stroma: Fluid found surrounding the thylakoids where light-independent photosynthesis, Calvin Cycle, occurs.

  • Chlorophyll: Green pigment capturing light energy.

Structure of Chloroplast

Structure of Chlorophyll

Chlorophyll is one of the major pigments in photosynthesis that captures light energy and gives green colour to plants. Understanding its working mechanism in the process of photosynthesis thus requires knowing its structure.

  • Molecular Structure: The molecule of chlorophyll contains a porphyrin ring—a large ring structure comprising a magnesium ion within its nucleus.
  • Types of Chlorophyll: There exist two main types of chlorophyll, chlorophyll a and chlorophyll b. Both are commonly found in vegetation.
  • Function: Chlorophyll is a green pigment that generally absorbs light in the blue and red regions of the visible spectrum, reflecting very little green light.

Photosynthetic Pigments

Photosynthetic pigments are molecules that absorb light energy for photosynthesis. The main types include:

  • Chlorophylls: Chlorophyll a (primary pigment) absorbs blue-violet and red light, while chlorophyll b captures blue and orange light, giving plants their green colour.
  • Carotenoids: These pigments absorb blue-green and violet light and reflect yellow, orange, and red. They protect plants by absorbing excess light.
  • Phycobilins: Found in algae, these pigments absorb green, yellow, and orange light, allowing photosynthesis in low-light conditions.

Stages of Photosynthesis

Photosynthesis occurs in two fundamental stages: light-dependent reactions and the Calvin Cycle. It used to be called light-independent reactions. The two stages collaboratively engage in converting light energy into the chemical energy housed within glucose.

Light-Dependent Reactions

  • Location: Light-dependent reactions occur within the thylakoid membranes of the chloroplasts.

  • Absorption of Light: Chlorophyll and other pigments absorb light energy, and the excited electrons undergo excitation.

H2O → 4 H+ + 4 e− + O2

ATP Formation And NADPH Formation

  • Electrons excited as described are passed down an electron transport chain, where ATP and NADPH are produced.

  • Formation of Glucose: The G3P molecules formed combine to form glucose and other carbohydrates.

The light-dependent reactions are the first of the two phases in photosynthesis, and they occur in the initial stage.

  • It is in these reactions that the chlorophyll contained in the light is being absorbed.

  • The absorbed energy of the light is transferred into chemical energy in the form of NADPH and ATP.

  • The reactions depend on light and occur along the thylakoid membranes of a chloroplast.

  • Location: thylakoid membrane

  • Sunlight and Chlorophyll: Upon the arrival of light

  • Photolysis of Water Sunlight splits water molecules to produce oxygen, protons, and electrons.

  • Energy from excited electrons creates ATP and NADPH through the electron transport chain.

Light Dependent Reaction

The Calvin Cycle (Light-Independent Reactions)

The Stroma of the chloroplast is the site of the actions in the Calvin cycle.

  • CO2 fixation: CO2 is incorporated into a 5-carbon sugar (RuBP) by the ribulose bisphosphate car.

  • RuBP Regeneration: Some of the G3P produced is used in the formation of glucose and other carbohydrates, while some combine with ATP to regenerate more RuBP.

  • The Calvin cycle, otherwise light-independent reactions, occurs in the stroma of the chloroplasts.

  • This process utilises the ATP and NADPH acquired from the light-dependent reactions to synthesise glucose from carbon dioxide.

  • Location: Stroma

  • Role of ATP and NADPH: Provides the energy and reducing power for carbon fixation and sugar synthesis.

Steps of the Calvin Cycle

  • Carbon Fixation: CO2 is fixed into a 5-carbon sugar (RuBP) by the enzyme Ru­bisco.

  • Reduction Phase: ATP and NADPH reduce 3-PGA to G3P.

  • RuBP Regeneration: ATP regenerates RuBP from G3P.

Calvin Cycle

Factors Affecting Photosynthesis

Several environmental factors affect photosynthesis and therefore its efficiency and rate. Understanding them is crucial for optimising the growth and productivity of plants.

  • Light Intensity: It is one of the limiting factors of photosynthesis up to a given point. The higher the light intensity, the higher the rate.

  • Carbon Dioxide Concentration: The level of CO2 may limit the rate of photosynthesis; higher values may result in higher rates.

  • Temperature: Enzymatic activities linked with photosynthesis are temperature-dependent.

  • Water: Availability of water is a necessity for photolysis and the general water needs of a typical plant.

C3, C4, And CAM Pathways

  • The different plants show variation in the photosynthetic pathways, and it seems that each one of them is adapted to some specific environment.

  • So, C3, C4, and CAM plants have their strategies to take up the process of photosynthesis in that particular environment.

Differences Between C3, C4, and CAM Plants

  • C3: This is the most common pathway; RuBP is used for carbon fixation.

  • C4: Minimises photorespiration; adapted to high light intensity and temperature.

  • CAM: Reduces transpiration; adapted to arid conditions.

  • Adaptations: Each type has evolved in some particular ecological habitats.

Examples

  • C3: Wheat, rice

  • C4: Maize, sugarcane

  • CAM: Cacti, succulents

Importance of Photosynthesis

Photosynthesis is essential for life on Earth. There will be many ecological implications, but photosynthesis also derives some practical benefits for the living world. As such, photosynthesis is among the most important biological processes.

  • Role in the Carbon Cycle: CO2 is converted into organic compounds, leading to a decrease in atmospheric CO2.

  • Production of Oxygen: Formulation of the oxygen.

  • The base of the Food Chain: It serves as the basic source of energy for all trophic levels.

  • Agriculture and Renewable Energy Applications: Improved crop yields and artificial photosynthesis are being researched as a means of sustainable energy production.

Also Read:

Difference between Light and Dark ReactionDifference between Photooxidation and Photorespiration
Photosynthesis and Chemiosmotic HypothesisBiological Pigments in Plants
Light Harvesting ComplexC4 and CAM Pathway

Recommended Video on 'Photosynthesis'

Frequently Asked Questions (FAQs)

1. What is photosynthesis and why is it important?

Photosynthesis is the process through which plants convert light energy into chemical energy stored in glucose which forms the base of the food chain, and produces oxygen that is essential for life.

2. How light-dependent and light-independent reactions are unlike in photosynthesis?

Light-dependent reactions convert light energy into chemical energy in the form of ATP and NADPH, while light-independent reactions use this energy for the production of glucose from CO2.

3. What factors regulate the rate of photosynthesis in plants?

The factors that regulate the rate of the process in plants are light intensity, CO2 concentration, temperature, and water availability.

4. Explain the differences between C3, C4, and CAM photosynthesis pathways.

C3 plants perform the standard photosynthetic pathway; C4 plants, adapted to high light- and temperature stress, work at reducing photorespiration as much as possible. On the other hand, CAM plants are adapted to arid environments by opening their stomata during the night.

5. What potential does artificial photosynthesis have toward renewable energy solutions?

Artificial photosynthesis is the replication of natural photosynthesis for the sustainable synthesis of fuels and chemicals, likely creating thereby a clean and renewable energy source.

6. Explain the process of photosynthesis

Photosynthesis is the process by which plants use sunlight to convert water and carbon dioxide into glucose and oxygen. This occurs in chloroplasts through light-dependent reactions, which capture energy from sunlight, and the Calvin cycle, which uses this energy to produce glucose. The process provides food for the plant and releases oxygen into the atmosphere.  

7. What is photorespiration, and why is it considered inefficient?
Photorespiration is a process that occurs when the enzyme RuBisCO fixes oxygen instead of carbon dioxide. It's considered inefficient because it uses energy without producing glucose and can reduce photosynthetic output by up to 25% in some plants. C4 and CAM plants have evolved mechanisms to minimize photorespiration.
8. How do desert plants perform photosynthesis?
Many desert plants use CAM (Crassulacean Acid Metabolism) photosynthesis. They open their stomata at night to collect CO2, store it as an organic acid, and use it for photosynthesis during the day when their stomata are closed. This adaptation helps conserve water in hot, dry environments.
9. How do plants capture carbon dioxide for photosynthesis?
Plants capture carbon dioxide through small pores called stomata, primarily located on the undersides of leaves. Stomata can open and close to regulate gas exchange and water loss.
10. What is the difference between C3 and C4 photosynthesis?
C3 photosynthesis is the most common type, where CO2 is fixed directly into a 3-carbon compound. C4 photosynthesis involves an additional step where CO2 is first fixed into a 4-carbon compound before entering the Calvin cycle. C4 plants are better adapted to hot, dry environments.
11. How does the structure of a leaf facilitate photosynthesis?
Leaf structure is optimized for photosynthesis:
12. What is the role of rubisco in photosynthesis?
Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) is a key enzyme in the Calvin cycle. It catalyzes the first major step of carbon fixation, attaching CO2 to a 5-carbon sugar to form two 3-carbon compounds. It's the most abundant protein on Earth but is relatively inefficient.
13. What is the quantum yield of photosynthesis?
The quantum yield of photosynthesis refers to the amount of carbon fixed or oxygen evolved per photon of light absorbed. It's a measure of photosynthetic efficiency:
14. How do plants adjust their photosynthetic capacity seasonally?
Plants adjust their photosynthetic capacity seasonally through:
15. How do plants protect photosystem II from damage during high light stress?
Plants protect photosystem II from high light stress through:
16. How do plants balance water loss and CO2 uptake during photosynthesis?
Plants balance water loss and CO2 uptake through stomatal regulation:
17. How do aquatic plants perform photosynthesis?
Aquatic plants have adaptations for photosynthesis in water:
18. How do plants protect themselves from excess light energy?
Plants protect themselves from excess light energy through several mechanisms:
19. How does the concentration of carbon dioxide affect photosynthesis?
CO2 concentration affects photosynthesis rate:
20. How do plants acclimate to different light environments?
Plants acclimate to different light environments through:
21. How does temperature affect photosynthesis?
Temperature affects the rate of photosynthesis. Generally, as temperature increases, the rate of photosynthesis increases up to an optimal point. Beyond this optimal temperature, enzyme activity decreases, and the rate of photosynthesis declines. The optimal temperature varies among plant species.
22. What is the light compensation point in photosynthesis?
The light compensation point is the light intensity at which the rate of photosynthesis exactly matches the rate of respiration. At this point, the plant neither gains nor loses carbon. Below this point, the plant uses more energy than it produces.
23. How do different wavelengths of light affect photosynthesis?
Different wavelengths of light affect photosynthesis to varying degrees. Red and blue light are most effective for photosynthesis, while green light is largely reflected (hence plants appear green). This is due to the absorption spectrum of chlorophyll and other photosynthetic pigments.
24. How do plants respond to changes in light intensity?
Plants respond to changes in light intensity through various mechanisms:
25. How do plants adapt to low-light conditions?
Plants adapt to low-light conditions through various strategies:
26. Why is photosynthesis important?
Photosynthesis is crucial because it produces oxygen, which most organisms need to survive, and it converts inorganic carbon (CO2) into organic compounds (sugars) that form the basis of most food chains. It also helps regulate the Earth's carbon cycle and climate.
27. What is the Calvin cycle, and why is it important?
The Calvin cycle, also known as the light-independent reactions or dark reactions, is the stage of photosynthesis where carbon dioxide is fixed into glucose. It's important because it's the process that actually produces the sugars that plants use for energy and growth.
28. What is the relationship between photosynthesis and cellular respiration?
Photosynthesis and cellular respiration are complementary processes. Photosynthesis produces glucose and oxygen, which are then used in cellular respiration to produce energy (ATP). The CO2 released by respiration can be used again in photosynthesis, creating a cycle.
29. What is the importance of the light-dependent reactions?
The light-dependent reactions are crucial because they:
30. How do plants coordinate nuclear and chloroplast gene expression for photosynthesis?
Coordination of nuclear and chloroplast gene expression involves:
31. What is the basic equation for photosynthesis?
The basic equation for photosynthesis is:
32. What is cyclic electron flow in photosynthesis?
Cyclic electron flow is an alternative electron transport pathway in photosynthesis:
33. What is the importance of the proton gradient in photosynthesis?
The proton gradient is crucial in photosynthesis:
34. What is the role of chlorophyll in photosynthesis?
Chlorophyll is the primary pigment responsible for absorbing light energy in photosynthesis. It primarily absorbs red and blue light while reflecting green light, giving plants their characteristic color. Chlorophyll initiates the light-dependent reactions by becoming excited when it absorbs light energy.
35. What is the role of carotenoids in photosynthesis?
Carotenoids are accessory pigments that:
36. What is the role of magnesium in photosynthesis?
Magnesium plays several crucial roles in photosynthesis:
37. How does the structure of chloroplasts support photosynthesis?
Chloroplast structure is optimized for photosynthesis:
38. Where does photosynthesis occur in plant cells?
Photosynthesis primarily occurs in the chloroplasts of plant cells. Chloroplasts are organelles that contain chlorophyll and other pigments necessary for capturing light energy.
39. What are the two main stages of photosynthesis?
The two main stages of photosynthesis are:
40. What is the role of ATP in photosynthesis?
ATP (Adenosine Triphosphate) serves as an energy currency in photosynthesis. It's produced during the light-dependent reactions and used in the Calvin cycle to power the reactions that fix carbon dioxide into glucose.
41. What is the role of NADPH in photosynthesis?
NADPH (Nicotinamide Adenine Dinucleotide Phosphate) is a reducing agent produced during the light-dependent reactions. It provides the electrons needed to reduce carbon dioxide to glucose in the Calvin cycle.
42. What is the significance of the Z-scheme in photosynthesis?
The Z-scheme represents the flow of electrons in the light-dependent reactions:
43. What is the role of water in photosynthesis?
Water plays several crucial roles in photosynthesis:
44. What is photosynthesis?
Photosynthesis is the process by which plants and other organisms convert light energy into chemical energy stored in glucose or other sugars. This process is essential for life on Earth as it produces oxygen and serves as the basis for most food chains.
45. What is the relationship between photosynthesis and photoperiodism?
While photosynthesis and photoperiodism are distinct processes, they are related:
46. How do plants respond to prolonged darkness?
Plants respond to prolonged darkness through various mechanisms:
47. What is the role of state transitions in photosynthesis?
State transitions are short-term adaptations to changes in light quality:
48. How do C4 plants concentrate CO2 for rubisco?
C4 plants concentrate CO2 for rubisco through spatial separation:
49. What is the role of iron in photosynthesis?
Iron plays several important roles in photosynthesis:

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