What is Photosynthesis? – Complete NCERT Notes

Introduction

Photosynthesis is the process by which green plants prepare their own food using sunlight, carbon dioxide, and water. It is one of the most important biological processes because it provides food and oxygen for almost all living organisms on Earth.

Definition of Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria make food (glucose) from carbon dioxide and water in the presence of sunlight and chlorophyll, releasing oxygen as a by-product.

Why is Photosynthesis Important?

Photosynthesis is important because:

It provides food for plants.
It forms the base of all food chains.
It releases oxygen needed for respiration.
It helps maintain the balance of oxygen and carbon dioxide in the atmosphere.
It stores solar energy in the form of chemical energy.

Raw Materials Required for Photosynthesis

Requirement	Source	Function
Sunlight	Sun	Provides energy
Carbon Dioxide (CO₂)	Air	Raw material for food production
Water (H₂O)	Soil	Required for glucose formation
Chlorophyll	Green leaves	Traps sunlight

Site of Photosynthesis

Photosynthesis mainly occurs in the leaves.
Leaves contain green-colored pigment called chlorophyll.
Chlorophyll is present in structures called chloroplasts.
Chloroplasts absorb sunlight and initiate food production.

Equation of Photosynthesis

The simplified chemical equation is:

6CO₂+6H₂O -> C₆H₁₂O₆+6O₂

Meaning:

Carbon dioxide + Water → Glucose + Oxygen
Sunlight and chlorophyll are necessary for this reaction.

Steps of Photosynthesis

1. Absorption of Sunlight

Chlorophyll absorbs sunlight from the sun.
Solar energy is captured and converted into chemical energy.

2. Absorption of Water

Roots absorb water from the soil.
Water is transported to leaves through xylem vessels.

3. Intake of Carbon Dioxide

Carbon dioxide enters the leaves through tiny pores called stomata.

4. Formation of Glucose

Carbon dioxide and water combine in the presence of sunlight.
Glucose (food) is produced.

5. Release of Oxygen

Oxygen is released through stomata into the atmosphere.

Role of Chlorophyll

What is Chlorophyll?

Chlorophyll is a green pigment present in plant leaves.

Functions of Chlorophyll

Absorbs sunlight.
Converts solar energy into chemical energy.
Enables photosynthesis.
Gives green color to plants.

Role of Stomata in Photosynthesis

Feature	Description
Location	Mostly on leaf surface
Structure	Tiny pores surrounded by guard cells
Function	Exchange of gases
During Photosynthesis	CO₂ enters and O₂ exits

Factors Affecting Photosynthesis

1. Light Intensity

More sunlight generally increases photosynthesis.
Very low light reduces food production.

2. Carbon Dioxide Concentration

Adequate CO₂ is necessary.
Low CO₂ decreases the rate of photosynthesis.

3. Water Availability

Water shortage slows photosynthesis.
Severe deficiency may stop the process.

4. Temperature

Moderate temperature is best.
Extremely high or low temperatures reduce photosynthesis.

5. Chlorophyll Content

Healthy green leaves perform photosynthesis efficiently.
Less chlorophyll means lower photosynthetic activity.

Evidence that Photosynthesis Produces Starch

Iodine Test

NCERT demonstrates that:

A leaf is boiled in water.
It is then boiled in alcohol to remove chlorophyll.
The leaf is washed and iodine solution is added.
The leaf turns blue-black, indicating the presence of starch.

Conclusion

Starch is produced during photosynthesis.
Starch is stored food in plants.

Photosynthesis and Food Chain

Photosynthesis is the foundation of all food chains.

Example

Level	Organism
Producer	Green Plant
Primary Consumer	Grasshopper
Secondary Consumer	Frog
Tertiary Consumer	Snake
Top Consumer	Eagle

Without photosynthesis, food chains cannot exist.

Difference Between Photosynthesis and Respiration

Photosynthesis	Respiration
Produces food	Breaks down food
Occurs in chloroplasts	Occurs in mitochondria
Uses CO₂	Uses O₂
Releases O₂	Releases CO₂
Stores energy	Releases energy

Key NCERT Points to Remember

Photosynthesis occurs in green plants.
Chlorophyll traps solar energy.
Carbon dioxide enters through stomata.
Water is absorbed by roots.
Glucose is produced as food.
Oxygen is released into the atmosphere.
Photosynthesis supports life on Earth.
It is the primary source of food and oxygen.

Practice Questions

Short Answer Questions

1. What is photosynthesis?

Answer: Photosynthesis is the process by which green plants prepare food using sunlight, carbon dioxide, and water in the presence of chlorophyll.

2. Which pigment is essential for photosynthesis?

Answer: Chlorophyll.

3. Where does photosynthesis occur?

Answer: In the chloroplasts of green leaves.

4. Which gas is released during photosynthesis?

Answer: Oxygen.

5. Through which structures does carbon dioxide enter leaves?

Answer: Through stomata.

Long Answer Questions

1. Explain the process of photosynthesis.

Answer:

Roots absorb water from soil.
Carbon dioxide enters through stomata.
Chlorophyll absorbs sunlight.
Water and carbon dioxide combine to form glucose.
Oxygen is released as a by-product.

2. Why is photosynthesis important?

Answer:

Produces food for plants.
Provides oxygen.
Maintains atmospheric balance.
Supports food chains.
Stores solar energy as chemical energy.

Fill in the Blanks

Photosynthesis occurs mainly in ________.
Answer: leaves
Green pigment present in leaves is called ________.
Answer: chlorophyll
Carbon dioxide enters leaves through ________.
Answer: stomata
Oxygen is released during ________.
Answer: photosynthesis
Water is absorbed by the ________.
Answer: roots
Glucose is the ________ prepared by plants.
Answer: food
Chlorophyll traps ________ energy.
Answer: solar
Photosynthesis helps maintain the balance of oxygen and ________.
Answer: carbon dioxide
Starch test uses ________ solution.
Answer: iodine
Chloroplasts contain ________.
Answer: chlorophyll

MCQs (Multiple Choice Questions)

1. Photosynthesis occurs mainly in:

A. Roots
B. Stem
C. Leaves
D. Flowers

Answer: C. Leaves

2. Green pigment in plants is:

A. Hemoglobin
B. Chlorophyll
C. Melanin
D. Carotene

Answer: B. Chlorophyll

3. Which gas is used during photosynthesis?

A. Oxygen
B. Nitrogen
C. Carbon Dioxide
D. Hydrogen

Answer: C. Carbon Dioxide

4. Which gas is released during photosynthesis?

A. Carbon Dioxide
B. Nitrogen
C. Hydrogen
D. Oxygen

Answer: D. Oxygen

5. Water is absorbed by:

A. Leaves
B. Flowers
C. Roots
D. Fruits

Answer: C. Roots

6. Photosynthesis converts solar energy into:

A. Mechanical energy
B. Chemical energy
C. Electrical energy
D. Sound energy

Answer: B. Chemical energy

7. Tiny pores on leaves are called:

A. Chloroplasts
B. Guard Cells
C. Stomata
D. Veins

Answer: C. Stomata

8. Food produced during photosynthesis is:

A. Protein
B. Fat
C. Glucose
D. Vitamin

Answer: C. Glucose

9. The starch test uses:

A. Salt solution
B. Iodine solution
C. Sugar solution
D. Lime water

Answer: B. Iodine solution

10. Photosynthesis is essential because it:

A. Produces oxygen
B. Produces food
C. Supports life on Earth
D. All of these

Answer: D. All of these

Quick Revision

✔ Photosynthesis = Food-making process in green plants
✔ Raw materials = CO₂ + Water + Sunlight + Chlorophyll
✔ Food produced = Glucose
✔ By-product = Oxygen
✔ Site = Chloroplasts in leaves
✔ Gas enters = Carbon dioxide through stomata
✔ Gas released = Oxygen
✔ Importance = Food, oxygen, and energy source for life on Earth