Class 7 Science

Respiration: Process of Breathing

The breathing is controlled by the movement of diaphragm. Diaphragm is a membrane which is between the chest and abdomen. The movement of diaphragm is controlled by a group of muscles; called intecostalis muscles.


process of inhalation

When the diaphragm moves down, the ribcage expands. This leads to the expansion inside the lungs. As a result, the air moves into the lungs. This process is called inspiration or inhalation.


process of exhalation

When the diaphragm moves up, the ribcage contracts. This leads to contraction of the lungs. As a result, the air moves out of the lungs. This process is called expiration or exhalation.

To show that carbon dioxide is released during exhalation:

Carbon dioxide reacts with limewater to make calcium carbonate. This property is utilized to show the evolution of carbon dioxide during respiration. For this, take a test tube and pour some limewater in it. Dip a drinking straw in the test tube. Blow air in the limewater through the drinking straw. It is observed that the limewater turns milky. This shows that carbon dioxide is released during exhalation.

Review Questions:

What is breathing?

Answer: The process of taking in and giving out air; for respiration; is called breathing.

What is the respiratory organ in humans?

Answer: Lungs

Which membrane controls the movement of lungs?

Answer: Diaphragm

Breathing in Other Animals

Animals, which belong to amphibia, reptilian, aves and mammalia, use the lungs for breathing. Amphibians breathe through their skin, when they are in water. Smaller animals have different organs for breathing.

Breathing in Fish

Fish have a pair of gills. They breathe air, dissolved in water, through gills. Water enters through mouth and exits through gills. When water passes through the gills, oxygen goes to blood capillaries inside the gills. At the same time, carbon dioxide from blood capillaries goes out and mixes with water. That is how, exchange of gases takes place in fish.

Breathing in Cockroach

Cockroach and other insects breathe through spiracles and tracheae. There is a network of hollow tubes running through the body of an insect. These hollow tubes are called tracheae. Each trachea opens on the body surface in the form of very small pore. These pores are called spiracles which are present on lateral sides of the cockroach. Air enters through spiracles and goes to tracheae.

Breathing in Earthworm

Earthworms breathe through their skin. The skin of earthworm always remains moist, which helps in breathing. Air enters through skin due to diffusion.

Breathing in Unicellular Animals

Unicellular animals breathe through the cell membrane. Air passes through cell membrane due to diffusion. Thus, exchange of gases in unicellular animals happens through diffusion.

Breathing in Plants

Plants can be of various sizes. Developing respiratory organs could not be a fruitful solution for plants, because of their unlimited growth. Each plant part breathes through its external layer of cells. Roots breathe through root hairs. Stems breathe through epidermis. Leaves have numerous small pores; called stomata; for breathing.

Review Questions:

What is the respiratory organ in fish?

Answer: Gills

What is the respiratory organ in cockroach?

Answer: Spiracles and tracheae

Which organ is used by a frog for breathing under water?

Answer: Skin