NCERT Class 7 Science Chapter 10: Respiration in Organisms YouTube Lecture Handouts

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NCERT Class 7 Science Chapter 10: Respiration in Organisms

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  • What is the movement of diaphragm and ribs during inhalation?

  • Why does muscle cramps occur?

  • Why does lime water turn milky when we blow air in it?

  • Why does dough rise and smells?


  • Breathing is part of respiration

  • Why running makes breathing faster?

  • Cell: Smallest structural and functional unit of an organism.

  • Each cell performs some function and needs energy for the same

  • Food has stored energy which is released during respiration

  • Cellular respiration: In the cells, oxygen in the air helps in the breakdown of food. The process of breakdown of food in the cell with the release of energy. It takes place in the cells of all organisms

  • Aerobic (with oxygen) & anaerobic (without oxygen)

  • Yeast can survive in absence of oxygen and are anaerobes – yield alcohol

  • Muscles can respire anaerobically for short time when there is deficiency of oxygen – running fast, cycling, walking, weight lifting – this reason for muscle cramps (accumulation of lactic acid) – relief by hot water bath or massage – it improves circulation of blood and oxygen supply increases


  • Inhalation – taking oxygen in

  • Exhalation – throwing out

  • Continuous process throughout life

  • Breathing rate – number of times a person breathes in a minute

  • Breathing = inhalation + exhalation

  • When person needs extra energy they breathe faster – more oxygen is supplied; speeds breaking down of food and more energy is released

  • An adult human being at rest breathes in and out 15–18 times in a minute. During heavy exercise, the breathing rate can increase upto 25 times per minute.

  • During exercise – we breathe fast; take deep breathe and inhale more oxygen

How do we breathe?

  • Nostrils (have hairs) Nasal Cavity Windpipe Lungs (in chest cavity)

  • Chest cavity is surrounded by ribs

  • Muscular diaphragm forms floor of chest cavity

  • Breathing involves movement of chest and diaphragm

👉 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.

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

- How do we breathe?

- How Do We Breathe?

- How do we breathe?

👉 If you exhale on mirror, moisture appears

Movement of the diaphragm helps in breathing

  • Regular traditional breathing exercise (pranayama) can increase the capacity of lungs to take in more air. Thus more oxygen can be supplied to the body cells resulting in release of more energy.

  • Inhaled air (21% and 0.04% )

  • Exhaled air (16.4% and 4.4% )

  • When we blow into the lime water, it turns milky. This is due to presence of in exhaled air

  • Cold morning: air from mouth appears like smoke - On a cold day, the warm and moist air exhaled by us condenses into mist when it comes in contact with the cold air of the atmosphere. This looks like white smoke.

  • Yawning: During drowsiness, our breathing rate slows down. The lungs do not get enough oxygen from the air resulting in yawning. Yawning brings extra oxygen into the lungs and helps us to keep awake

Breathing in Organisms

  • Mammals have lungs

  • Cockroach – small openings on side of body called spiracles & led to network of air tubes called trachea for gas exchange. Oxygen rich air rushes through spiracles into the tracheal tubes, diffuses into body tissue, and reaches every cell of body.

  • Earthworms – breathe through skin (moist and slimy) – gas can pass through them

  • Frogs – pair of lungs and can breathe through skin (moist and slippery)

  • Fishes – Gills (projections of skin) – gills are supplied with blood vessels for exchange of gases

  • Plants respire by taking in and giving out – leaves have stomata (lower surface; more in number than spiracles) for exchange of . Root cells also require oxygen – they take air from air spaces between soil particles

  • For us oxygen is essential, but for those organisms which do not use it,

  • oxygen is toxic. In fact, for humans and other organisms it may be

  • dangerous to breathe pure oxygen for long.

- Image of plants oxygen

- Image of Plants Oxygen

- Image of plants oxygen

  • Highest in last jar & in 1st jar released is used in photosynthesis

  • Dough has yeast and rises – due to ; smells due to conversion to alcohol; sugar added to dough is food for yeast. At low temperatures, yeasts will not multiply and respire because of which the dough will not rise or become sour.

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