Life Process Notes for Class 10 Biology : Respiration in animals

These are the CBSE class 10 biology notes on chapter Life Process : Respiration in animals Topics covered in this page are

  1. Respiration in animals
  2. Respiration in Amoeba
  3. Respiration in Earthworm
  4. Respiration in Fish
  5. Respiratory system in Humans
  6. Mechanism of Respiration
  7. Rate of breathing
  8. Carbon monoxide poisoning

Respiration in Animals

  • Different animals have different modes of respiration.


    Respiratory organ

    Unicellular animals like Amoeba, Planaria

    Cell membrane



    Aquatic animals like Fish, Prawns


    Insects like Grasshopper, Cockroach

    Spiracles and tracheae

    Land animals like Humans, birds


  • All the respiratory organs have three common features:
    1. All the respiratory organs have a large surface area to get enough oxygen.
    2. All the respiratory organs have thin walls for easy diffusion and exchange of respiratory gases.
    3. All the respiratory organs like skin gills, and lungs have a rich blood supply for transporting respiratory gases.
  • Terrestrial animals can breathe the oxygen in the atmosphere, but animals that live in water (aquatic animals) need to use the oxygen dissolved in water.
  • Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.

Respiration in Amoeba:

  • Amoeba is single-celled animal. Amoeba depends on simple diffusion of gases from breathing.
  • The exchange of gases in Amoeba takes place through its cell membrane.
  • Amoeba lives in water. This water has oxygen dissolved in it. The oxygen from water diffuses into the body of Amoeba through its cell membrane.
  • Since the amoeba is very small in size, so the oxygen spreads quickly into the whole body of Amoeba.
  • This oxygen is used for respiration inside the Amoeba cell. The process of respiration produces carbon dioxide gas continuously. This carbon dioxide gas diffuses out through the membrane of amoeba into the surrounding water.

Respiration in Earthworm:

  • The earthworm exchanges the gases through its skin. The earthworm absorbs the oxygen is needed for respiration through is moist skin.
  • The oxygen is then transported to all the cells of the earthworm by its blood where it is used in respiration.
  • The carbon dioxide produced during respiration is carried back by the blood. This CO2 is expelled from the body of the earthworm through its skin.  

Respiration in Fish:

  • The fish has special organs for breathing called ‘gills’. The fish has gills on both the sides of its head.
  • The fish lives in water and this water contains dissolves oxygen in it. The fish breathes by taking in water through its mouth and sending it over the gills.
  • When water passes over gills, the gills extract dissolved oxygen from this water. The water then goes out through the gill slits.
  • The extracted oxygen is absorbed by the blood and carried to all the parts of the fish. The carbon dioxide produced by the respiration is brought back by the blood into the gills for expelling into the surrounding water.

    Note: diffusion is insufficient to meet the oxygen requirements of large multicellular organisms like humans because the volume of human body is so big that oxygen cannot diffuse into all the cells of the human body quickly.

Respiratory system in Humans

  • In human beings, many organs take part in the process of respiration. These organs are called organs of respiratory system.
  • The main organs of human respiratory system are: Nose, Nasal passage, Trachea (wind pipe), Bronchi, Lungs and Diaphragm.
  • The human respiratory system begins from the nose. The air then goes into nasal passage. The nasal passage is lined is lined with fine hair and mucus.
  • When air passes through the nasal passage, the dust particles and other impurities present in it are trapped by nasal hair and mucus so that clean air goes into lungs.
  • The part of throat between the mouth and wind pipe is called pharynx.
  • From the nasal passage, air enters into pharynx and then goes into the wind pipe. Trachea does not collapse even when there is no air in it because it is supported by rings of soft bones called cartilage.
  • The trachea runs down the neck and divides into two smaller tubes called bronchi at its lower end.
  • The bronchi are connected to the two lungs. The lungs lie in the chest cavity or thoracic cavity which is separated from abdominal cavity by a muscular partition called diaphragm.
  • Each bronchus divides in the lungs to form a large number of still smaller tubes called ‘bronchioles’.
  • The pouch-like air sacs at the ends of the smallest bronchioles are called alveoli.
  • The walls of alveoli are very thin and they are surrounded by very thin blood capillaries.
  • It is in the alveoli that gaseous exchange takes place.

Mechanism of Respiration:

  • When we breathe in, we lift our ribs and flatten our diaphragm. And the chest cavity becomes larger as a result. Because of this, air is sucked into the lungs and fills the expanded alveoli.
  • The alveoli are surrounded by thin blood vessels called capillaries carrying blood in them. So. The oxygen of air diffuses out from the alveoli walls into the blood.
  • The oxygen is carried by blood to all the parts of the body. As the blood passes through the tissues of the body, the oxygen present in it diffuses into the cells.
  • The oxygen combines with the digested food present in the cells to release energy.
  • Carbon dioxide gas is produced as a waste product during respiration in the cells of the body tissues. This carbon dioxide diffuses into the blood.
  • Blood carries the CO2 back to the lungs where it diffuses into the alveoli.
  • When we breathe out air. The diaphragm and muscles attached to the ribs relax due to which our chest cavity contracts and becomes smaller. This contraction movement of the chest pushes out CO2 from the alveoli of lungs into the trachea, nostrils then out of the body into air.
  • Note: During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.
  • Carbon dioxide is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood.

Rate of breathing:

  • The process of breathing pumps in oxygen into our body (and removes CO2).
  • Breathing occurs involuntarily but the rate of breathing is controlled by the respiratory system of brain.
  • The average breathing rate in an adult man at rest is about 15 to 18 times per minute. This breathing rate increases with increased physical activity.
    1. Oxygen required for breathing and respiration is carried by haemoglobin pigment present in our blood. The normal range of haemoglobin in the blood of a healthy adult person is from 12 to 18 grams per deciliter of blood.
    2. The deficiency of haemoglobin in the blood of a person reduces the oxygen carrying capacity of blood resulting in breathing problems, tiredness and lack of energy.

Carbon monoxide poisoning:

  • Carbon monoxide gas (CO) is formed whenever a fuel burns in an insufficient supply of air. For car engine. For example, if coal is burned in a closed space, then a lot of carbon monoxide is formed. CO produced when petrol burns in a car engine.
  • Haemoglobin has more affinity for carbon monoxide than oxygen, So, if carbon monoxide gas is inhaled by a person, then this carbon monoxide binds very strongly with haemoglobin in the blood and prevents it from carrying oxygen to the brain and other parts of the body.
  • Due to lack of oxygen, the person cannot breathe properly. If carbon monoxide is inhale for a

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