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Respiration in Organisms Class 7 Notes Science Chapter 6

Respiration is like the power source for our bodies, just like batteries power toys, or gadgets, respiration powers living things. It's a process that happens inside our cells, helping us get energy from the food we eat. 

What is Respiration?

Respiration is a fundamental process for all living organisms to obtain energy from food. During breathing, air containing oxygen is inhaled, and the exhaled air is rich in carbon dioxide. The inhaled air is transported throughout the body and eventually reaches each cell. Within the cells, oxygen facilitates the breakdown of food, a process known as cellular respiration. 

Respiration in OrganismsRespiration in Organisms

This vital process occurs in the cells of all living organisms. Respiration in organisms refers to the process by which living organisms obtain energy from the food they consume. 

Types of Respiration

Types of RespirationTypes of Respiration

1. Aerobic Respiration

Aerobic respiration is the process of breaking down nutrients (usually glucose) in the presence of oxygen to produce energy (ATP), carbon dioxide, and water.

C₆H₁₂O₆ (glucose) + 6O₂ (oxygen) → 6CO₂ (carbon dioxide) + 6H₂O (water) + Energy (ATP)

Examples of Aerobic Respiration: Humans

2. Anaerobic Respiration

Anaerobic respiration is the process of breaking down nutrients (such as glucose) without the use of oxygen. It is a less efficient process compared to aerobic respiration.

C₆H₁₂O₆ (glucose) → 2C₃H₆O₃ (lactic acid) + Energy (ATP)

Examples of Anaerobic Respiration: Yeast 

Note: Yeast, being unicellular organisms, undergo anaerobic respiration, producing alcohol in the process. This characteristic makes them valuable in the production of wine and beer.

Types of RespirationTypes of Respiration

Have you ever wondered about the cause of muscle cramps post-intense exercise?

These cramps arise from anaerobic respiration in muscle cells, leading to the production of lactic acid through partial glucose breakdown. The accumulation of lactic acid is responsible for the cramps.

Question for Chapter Notes: Respiration in Organisms
Try yourself:
What is the process by which living organisms obtain energy from the food they consume in the presence of oxygen?
View Solution


Breathing involves the intake of oxygen-rich air and the release of carbon dioxide-rich air through respiratory organs. Inhalation refers to the intake of oxygen, while exhalation is the expulsion of carbon dioxide. 

Inhalation and ExhalationInhalation and Exhalation

This continuous process occurs consistently throughout an organism's life. The frequency of breaths per minute is referred to as the breathing rate. Inhalation and exhalation occur in a repeating pattern during breathing, and each cycle, consisting of one inhalation followed by one exhalation, is considered a breath.

How do we Breathe?

The respiratory system plays a crucial role in breathing, and each part  (nostrils, nasal cavity, windpipe, lungs, ribs, and diaphragm) has a specific function in the process.

Parts of Human Respiratory System Parts of Human Respiratory System 

(a) Nostrils and Nasal Cavity

Function: When we inhale, air enters the body through the nostrils. The nasal cavity serves several functions, such as filtering, humidifying, and warming the incoming air. It also contains small hair-like structures called cilia, which help trap dust and particles.

(b) Windpipe (Trachea)

Function: The trachea is a tube that connects the nasal cavity to the lungs. It allows the passage of air between these two regions.

(c) Lungs

Function: Lungs are the primary organs of the respiratory system. Oxygen from the inhaled air diffuses into the blood, and carbon dioxide, a waste product, is released from the blood into the lungs to be exhaled. The exchange of gases (oxygen and carbon dioxide) occurs in the tiny air sacs called alveoli within the lungs.

(d) Chest Cavity and Ribs

Function: The lungs are located in the chest cavity, which is surrounded by ribs. The ribs protect the delicate organs within the chest, including the lungs. Additionally, the ribs play a role in the expansion and contraction of the chest during breathing.

(e) Diaphragm

Function: The diaphragm is a large, dome-shaped muscle that separates the chest cavity from the abdominal cavity. During inhalation, the diaphragm contracts and moves downward, increasing the volume of the chest cavity. This expansion lowers the air pressure in the lungs, causing air to rush in. During exhalation, the diaphragm relaxes and moves upward, reducing the volume of the chest cavity, and air is expelled from the lungs.

Two Phases of Breathing 

The breathing mechanism comprises two phases

  • Inhalation 
  • Exhalation.

Inhalation, an energy-demanding process, involves the simultaneous contraction of intercostal muscles and the diaphragm. This action moves the ribs outward and upward, expanding the thoracic cavity and increasing lung volume. The resulting decrease in air pressure within the lungs leads to the influx of air through the air passages.


Exhalation is initiated by the relaxation of intercostal muscles and the diaphragm, causing the ribs to return to their original position and the diaphragm to assume a dome shape. These movements reduce the thoracic cavity's volume, bringing the lungs back to their initial volume. As a consequence, air is expelled from the lungs due to increased pressure within them, surpassing atmospheric pressure.


Question for Chapter Notes: Respiration in Organisms
Try yourself:
What is the function of the diaphragm in the breathing process?
View Solution

What do we Breathe out? 

The respiratory system and the process of respiration, organisms, including humans, breathe out carbon dioxide (CO2). During cellular respiration, cells utilize oxygen to break down glucose and release energy.

Composition of Exhaled airComposition of Exhaled air

As a byproduct of this process, carbon dioxide is produced and transported back to the lungs, where it is expelled from the body when we exhale. Therefore, the primary gas breathed out during respiration is carbon dioxide.

Breathing in other Animals

Many animals, including elephants, lions, cows, goats, frogs, lizards, snakes, and birds, have lungs in their chest cavities similar to humans. However, other organisms have different respiratory systems.

(a) Cockroach:  Cockroach has small openings called spiracles on the sides of its body. Insects, including cockroaches, use a network of air tubes known as tracheae for gas exchange. Oxygen-rich air enters through spiracles into the tracheal tubes, diffuses into the body tissues, and reaches every cell. Carbon dioxide produced in the cells exits through the tracheal tubes and is expelled through spiracles. This system of air tubes or tracheae is unique to insects and is not present in other animal groups such as snails, fish, earthworms, ants, and mosquitoes.

Respiration in Organisms Class 7 Notes Science Chapter 6

(b) Earthworm: Earthworms and frogs have unique respiratory adaptations. Earthworms breathe through their skin, which is moist and slimy, allowing gases to easily pass through. Similarly, although frogs possess lungs like humans, they can also respire through their skin, which is moist and slippery.

Breathing under water

Can people breathe and live underwater? No, but some animals can. For example, fish have gills that help them extract oxygen from water. Gills are like skin extensions with lots of tiny blood vessels that help them breathe by exchanging gases.

Respiration in Organisms Class 7 Notes Science Chapter 6

Fish can breathe underwater because they have specialized organs called gills. Gills are located on the sides of a fish's head and are responsible for extracting oxygen from the water. Here's how it works:

  • Water intake: Fish take in water through their mouths by opening and closing their mouths.
  • Passage over gills: As water enters the fish's mouth, it passes over the gill filaments. These gill filaments are like thin sheets with a large surface area.
  • Oxygen exchange: Oxygen in the water diffuses across the thin walls of the gill filaments and into the blood vessels. At the same time, carbon dioxide, a waste product produced by the fish, diffuses out of the blood vessels and into the water.
  • Water exit: The now oxygen-depleted water is expelled through openings called gill slits on the sides of the fish.

Do Plants also Respire?

Similar to other living organisms, plants engage in respiration to ensure their survival. They, too, absorb oxygen from the air and release carbon dioxide. 

Within the cells, oxygen is utilized to break down glucose into carbon dioxide and water, mirroring the process in other organisms. Notably, each part of the plant can independently acquire oxygen from the air and expel carbon dioxide. As previously mentioned in Chapter 1, leaves possess minuscule openings called stomata that facilitate the exchange of oxygen and carbon dioxide. Just like all other living cells in plants, root cells also require oxygen to produce energy. Roots extract air from the gaps between soil particles for this purpose

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FAQs on Respiration in Organisms Class 7 Notes Science Chapter 6

1. What is respiration?
Ans. Respiration is the process by which organisms take in oxygen and release carbon dioxide. It is a vital process that helps in the production of energy.
2. What are the types of respiration?
Ans. There are two types of respiration: aerobic respiration and anaerobic respiration. Aerobic respiration occurs in the presence of oxygen and releases a large amount of energy, while anaerobic respiration occurs in the absence of oxygen and releases a smaller amount of energy.
3. How do we breathe?
Ans. Breathing is the process by which we inhale oxygen and exhale carbon dioxide. It involves the contraction and relaxation of muscles, such as the diaphragm and intercostal muscles, which help in the expansion and contraction of the lungs.
4. What do we breathe out?
Ans. We breathe out carbon dioxide, which is a waste product produced during the process of respiration. The inhaled oxygen is used by our cells to produce energy, and carbon dioxide is released as a byproduct.
5. Do plants also respire?
Ans. Yes, plants also respire. They take in oxygen through tiny pores called stomata present in their leaves and release carbon dioxide. However, plants also have the ability to carry out photosynthesis, which is the process of using sunlight to convert carbon dioxide into oxygen and glucose.
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