What is Respiration in Humans? – Complete NCERT-Based Notes

Introduction

Respiration is a vital life process through which living organisms obtain energy from food. In humans, respiration involves the intake of oxygen, breakdown of food (glucose), release of energy, and removal of carbon dioxide.

According to NCERT, respiration is the process in which food is broken down in the cells of the body to release energy required for various life activities.

SEO Keywords

What is respiration in humans
Human respiration notes
NCERT respiration chapter
Respiration in humans class 7
Human respiratory system
Aerobic respiration
Anaerobic respiration
Breathing and respiration difference

Definition of Respiration

Respiration is the biochemical process in which food (glucose) is broken down inside cells to release energy.

Basic Equation of Respiration

C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + Energy

This energy is used for:

Growth
Movement
Repair of tissues
Digestion
Circulation of blood
Brain functions

Difference Between Breathing and Respiration

Feature	Breathing	Respiration
Meaning	Physical process of inhaling and exhaling air	Chemical process of releasing energy from food
Occurs In	Lungs	Body cells
Energy Released	No	Yes
Nature	Mechanical process	Biochemical process
Controlled By	Respiratory muscles	Cellular enzymes

Important Note

Breathing is only a part of respiration. Respiration includes both breathing and energy release inside cells.

Human Respiratory System

The respiratory system consists of organs that help in breathing and gas exchange.

Main Parts

Nostrils
Nasal cavity
Pharynx
Larynx
Trachea (Windpipe)
Bronchi
Lungs
Alveoli
Diaphragm

Functions of Respiratory Organs

Organ	Function
Nostrils	Allow air to enter
Nasal Cavity	Filters, warms, and moistens air
Trachea	Carries air to lungs
Bronchi	Branches carrying air into lungs
Lungs	Main organs of respiration
Alveoli	Site of gas exchange
Diaphragm	Helps in breathing movements

What Happens During Breathing?

Breathing occurs in two stages:

1. Inhalation (Inspiration)

During inhalation:

Air rich in oxygen enters the lungs.
Ribs move upward and outward.
Diaphragm contracts and moves downward.
Chest cavity expands.

2. Exhalation (Expiration)

During exhalation:

Carbon dioxide-rich air leaves the lungs.
Ribs move downward and inward.
Diaphragm relaxes and moves upward.
Chest cavity decreases in size.

Gas Exchange in the Lungs

Inside the lungs are millions of tiny air sacs called alveoli.

In Alveoli

Oxygen passes into the blood.
Carbon dioxide moves from blood into alveoli.
Carbon dioxide is exhaled.

Importance of Alveoli

Very thin walls
Large surface area
Rich blood supply

These features make gas exchange efficient.

Cellular Respiration

After oxygen enters the blood, it reaches body cells.

Inside cells:

Glucose is broken down.
Oxygen is used.
Energy is released.
Carbon dioxide and water are produced.

This process is called cellular respiration.

Types of Respiration

1. Aerobic Respiration

Occurs in the presence of oxygen.

Characteristics

Requires oxygen
Produces large amount of energy
Produces carbon dioxide and water

Example: Normal respiration in humans.

2. Anaerobic Respiration

Occurs without oxygen.

Characteristics

Does not require oxygen
Produces less energy
Produces lactic acid in muscles

Example: During vigorous exercise when oxygen supply is insufficient.

Aerobic vs Anaerobic Respiration

Feature	Aerobic Respiration	Anaerobic Respiration
Oxygen Required	Yes	No
Energy Released	More	Less
End Products	Carbon dioxide + Water	Lactic acid
Occurs In	Normal body cells	Muscle cells during heavy exercise

Why Do We Breathe Faster During Exercise?

During exercise:

Muscles require more energy.
More oxygen is needed.
More carbon dioxide is produced.
Breathing rate increases to meet energy demands.

This is why we breathe heavily after running or playing sports.

Respiratory Rate

Definition

The number of breaths taken in one minute is called the respiratory rate.

Average Respiratory Rate

Person	Breaths per Minute
Adult at Rest	12–20
Child	20–30
Infant	30–60

Common Respiratory Diseases

Disease	Cause
Asthma	Narrowing of airways
Bronchitis	Inflammation of bronchi
Pneumonia	Infection of lungs
Tuberculosis (TB)	Bacterial infection
COVID-19	Viral infection affecting lungs

Prevention Tips

Avoid smoking.
Exercise regularly.
Maintain hygiene.
Eat nutritious food.
Avoid air pollution.

Importance of Respiration

Respiration is essential because it:

Provides energy for life processes.
Helps in growth and development.
Supports body movements.
Maintains body functions.
Removes waste carbon dioxide.

Flow Chart of Human Respiration

Food (Glucose)
↓
Oxygen Enters Body
↓
Lungs
↓
Blood
↓
Body Cells
↓
Energy Released
↓
Carbon Dioxide Produced
↓
Lungs
↓
Exhaled Out

Quick Revision Points

✅ Respiration releases energy from food.

✅ Oxygen is required for aerobic respiration.

✅ Lungs are the main respiratory organs.

✅ Alveoli are the sites of gas exchange.

✅ Carbon dioxide is removed from the body during exhalation.

✅ Cellular respiration occurs inside cells.

✅ Anaerobic respiration produces less energy.

✅ Breathing and respiration are not the same process.

Practice Questions

Very Short Answer Questions

1. What is respiration?

Answer: Respiration is the process of breaking down food to release energy.

2. Which gas is essential for aerobic respiration?

Answer: Oxygen.

3. What are alveoli?

Answer: Tiny air sacs in the lungs where gas exchange occurs.

4. Which gas is exhaled by humans?

Answer: Carbon dioxide.

5. What is the main organ of respiration?

Answer: Lungs.

Short Answer Questions

1. Differentiate between breathing and respiration.

Answer:

Breathing	Respiration
Physical process	Chemical process
Occurs in lungs	Occurs in cells
No energy released	Energy released

2. Why do we breathe faster during exercise?

Answer: During exercise muscles need more energy. Therefore, more oxygen is required and more carbon dioxide is produced, increasing the breathing rate.

3. What is aerobic respiration?

Answer: Aerobic respiration is the breakdown of food in the presence of oxygen to release energy.

Fill in the Blanks

Respiration releases ______ from food.
Answer: Energy
Tiny air sacs in lungs are called ______.
Answer: Alveoli
Aerobic respiration requires ______.
Answer: Oxygen
Carbon dioxide is removed during ______.
Answer: Exhalation
The ______ helps in breathing movements.
Answer: Diaphragm
Cellular respiration occurs inside ______.
Answer: Cells
The windpipe is also called the ______.
Answer: Trachea
Human beings inhale ______ gas.
Answer: Oxygen
Anaerobic respiration releases ______ energy than aerobic respiration.
Answer: Less
The lungs are located in the ______ cavity.
Answer: Chest

Answer: A

Conclusion

Respiration in humans is a life-sustaining process that releases energy from food. The respiratory system enables oxygen to enter the body and carbon dioxide to leave it. Through aerobic and anaerobic respiration, cells obtain the energy needed for growth, movement, repair, and all other vital activities. Understanding respiration helps explain how the human body functions and survives every day.