Section outline

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      Important terms:

      1. Cellular respiration is the process of breakdown of food (glucose) in the cell to release of energy.

      2. Aerobic respiration takes place in the presence of oxygen.

      3. Anerobic respiration takes place without oxygen.

      4. Breathing is taking in air rich in oxygen and giving out air rich in carbon dioxide with the help of respiratory organs.

      5. Inhalation is taking in air rich in oxygen into the body.

      6. Exhalation is giving out air rich in carbon dioxide,

      7. Breathing rate is the number of times a person breathes in a minute.

      8. A breath means one inhalation plus one exhalation.

      9. Spiracles are small openings on the sides of the bodies of the insects through which they breathe.

      10. Stomata are tiny pores present on the surface of the leaves through which exchange of gases takes place in plants.

       

      Key facts:

      1. Breathing rate of a person at rest is 15 to 18 times per minute.

      2. Breathing rate of a person during heavy exercise can increase to 25 times per minute.

      3. Inhaled air consists of 21% oxygen & 0.04% carbon dioxide.

      4. Exhaled air consists of 16.4% oxygen & 4.4% carbon dioxide.

    • Quick revision notes:
      1. Cellular respiration:
      • It is breaking down of food (glucose) to obtain energy.
      • Food has stored energy which is released during respiration.
      • This energy is used by the body for various functions and activities.
      2. Aerobic respiration:
      • Glucose breaks down with the help of oxygen to release a large amount of energy.
      • Mostly all multicellular animals, plants & humans respire anaerobically.
      3. Anaerobic respiration:
      • In this respiration, glucose  breakdown without oxygen.
      • It takes place in unicellular organisms like yeast.
      • As alcohol is yielded, yeast is used to prepare wines & beers.
      • It also takes place in muscles cells when we do heavy exercise due to lack of sufficient oxygen.
      • Here, partial breakdown of glucose takes place producing lactic acid which accumulates & causes muscle cramps.
      4. Breathing:
      • Taking in air rich in oxygen is inhalation.
      • Giving out air rich in carbon dioxide is exhalation.
      • The number of times a person breathes per minute is breathing rate.
      • Breathing is a part of respiration.
      5. Human respiratory system:
      • Respiratory organs consist of nostrils, nasal cavity, wind pipe or trachea, lungs & diaphragm.
      • Air enters through the nostrils and passes through the nasal cavity and then from wind pipe to the lungs.
      • Lungs are situated in the chest cavity surrounded by the ribs.
      • During inhalation, ribs move up and outwards and diaphragm moves down.
      • This movement increases space in our chest cavity and air rushes into the lungs and fills it up.
      • During exhalation, ribs move down and inwards, while diaphragm moves back to its position.
      • This reduces the size of the chest cavity and air is pushed out of the lungs.

      6. Breathing in animals:
      • Insects like cockroach breathe through tiny holes present on the sides of their bodies called spiracles. They have a network of air tubes called tracheae for gas exchange.
      • Earthworm breathes through moist & slimy skin.
      • Frog breathes through lungs on land & skin in water.
      • Fishes breathe through projections called gills on their skin.
      7. Breathing in plants:
      • Plants have tiny pores called stomata on the surfaces of leaves for gas exchange.
      • Root cells also need oxygen to generate energy which they take from the air spaces present between the soil particles.