CBSE – 7th Standard Science

Chapter 10 – Respiration in Organisms

Chapter 10

Respiration in Organisms

  • The cell needs energy to perform functions.
  • The food has stored energy, which is released during respiration. All living organisms respire to get energy from food.
  • During breathing, air containing oxygen is taken in and air rich in carbon dioxide is breath out.
  • The air we breathe in is transported to all parts of the body and ultimately to each cell. In the cells, oxygen in the air helps in the breakdown of food.
  • The process of breakdown of food in the cell with release of energy is called cellular respiration.
  • Cellular respiration takes place in the cells of all organisms.
  • In the cell, the food (glucose) is broken down into carbon dioxide and water using oxygen.
  • When breakdown of glucose occurs with the use of oxygen it is called aerobic respiration.
  • Food can also be broken down, without using oxygen. This is called anaerobic respiration.


  • Breakdown of food releases energy. Glucose (With the use of oxygen) = carbon dioxide + water + energy.


  • There are some organisms such as yeast that can survive in the absence of air. They are called anaerobes.
  • They get energy through anaerobic respiration. In the absence of oxygen, glucose breaks down into alcohol and carbon dioxide.
  • Breathing means taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs.
  • The taking in of air rich in oxygen into the body is called inhalation and giving out of air rich in carbon dioxide is known as exhalation.


  • The number of times a person breathes in a minute is termed as the breathing rate.
  • During breathing inhalation and exhalation take place alternately.
  •  A breath means one inhalation plus one exhalation.
  • Normally we take in air through our nostrils. inhaled air passes through our nostrils into the nasal cavity.
  • From the nasal cavity, the air reaches our lungs through the windpipe. Lungs are present in the chest cavity
  • A large, muscular sheet called diaphragm forms the floor of the chest cavity Breathing involves the movement of the diaphragm and the rib cage.
  • During inhalation, ribs move up and outwards and diaphragm moves down. This movement increases space in chest cavity and air rushes into lungs. The lungs get filled with air.
  • During exhalation, ribs move down and inwards, while diaphragm moves up to its former position.


  • This reduces the size of the chest cavity and air is pushed out of the lungs
  • Animals such as elephants, lions, cows, goats, frogs, lizards, snakes, birds, have lungs in their chest cavities like the human beings.
  • A cockroach has small openings on the sides of its body. Other insects also have similar openings. These openings are called spiracles.


  • Insects have a network of air tubes called tracheae for gas exchange.
  • Oxygen rich air rushes through spiracles into the tracheal tubes, diffuses into the body tissue, and reaches every cell of the body carbon dioxide from the cells goes into the tracheal tubes and moves out through spiracles.
  • These air tubes or tracheae are found only in insects and not in any other group of animals.
  • Earthworms breathe with their skins. The moist and slimy skin gases can easily pass through them.


  • Frogs have a pair of lungs like human beings, they can also breathe through their skin, which is moist and slippery.


  • Gills in fish help them to use oxygen dissolved in water.
  • Gills are projections of the skin an are well supplied with blood vessels for exchange of gases.
  • Plants also respire for their survival take in oxygen from the air and give out carbon dioxide.
  • In plants each part can independently take in oxygen from the air and give out carbon dioxide the leaves of the plants have tiny pores stomata for exchange of oxygen and carbon dioxide


  • The root cells also need oxygen to generate energy. Roots take up air from the air spaces present between the soil particles.
  • In the cells oxygen is used to break down glucose into carbon dioxide and water as in other organisms.
  • Respiration is essential for survival of living organisms. It releases energy from the food.
  • The oxygen we inhale is used to breakdown glucose into carbon dioxide and water. Energy is released in the process.
  • The breakdown of glucose occurs in the cells of an organism (cellular respiration).


  • If the food is broken down with the use of oxygen, it is called aerobic respiration. If the breakdown occurs
  • Without the use of oxygen, the respiration is called anaerobic respiration.
  • During heavy exercise when the supply of oxygen to our muscle cells is insufficient, food breakdown is by anaerobic respiration.
  • Breathing is a part of the process of respiration during which an organism takes in the oxygen-rich air and gives out air rich in carbon dioxide.
  • During inhalation, our lungs expand and then come back to the original state as the air moves out during exhalation.
  • In animals like cow, buffalo, dog and cat the respiratory organs and the process of breathing are similar to those in humans.
  • In earthworm, the exchange of gases occurs through the moist skin. In fishes it takes place through gills and in insects through the tracheae.
  • In a plant the roots take in air present in the soil. Leaves have tiny pores called stomata through which they exchange gases.
  • The breakdown of glucose in the plant cells is similar to that in other living beings.