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Science: Class 7 — Chapter 6: Respiration in Organisms

6.1 Why Do We Respire?

Cellular Respiration

  • Cell: The smallest structural and functional unit of an organism.
  • Cellular Respiration: The process of breakdown of food in the cell with the release of energy.
  • Aerobic Respiration: Breakdown of glucose in the presence of oxygen to release carbon dioxide, water, and energy.
  • Anaerobic Respiration: Breakdown of food without using oxygen, yielding alcohol, carbon dioxide, and energy (e.g., in yeast).
  • Anaerobes: Organisms like yeast that can survive in the absence of air.

Anaerobic Respiration in Muscles

  • Occurs during heavy exercise when oxygen supply is limited.
  • Glucose breaks down into lactic acid and energy.
  • Accumulation of lactic acid causes muscle cramps. Relief is obtained via hot water baths or massages which improve blood circulation and oxygen supply.
6.2 Breathing

Mechanism of Breathing

  • Breathing: Process of taking in air rich in oxygen (inhalation) and giving out air rich in carbon dioxide (exhalation).
  • Breathing Rate: Number of times a person breathes in a minute. Average adult at rest: 15-18 times/minute.
  • A single breath consists of one inhalation and one exhalation.
6.3 How Do We Breathe?

Human Respiratory System

  • Pathway: Nostrils → Nasal Cavity → Windpipe → Lungs (located in the chest cavity).
  • Diaphragm: A large, muscular sheet forming the floor of the chest cavity.
  • Inhalation: Ribs move up and outwards; diaphragm moves down. Chest cavity expands, drawing air into the lungs.
  • Exhalation: Ribs move down and inwards; diaphragm moves up. Chest cavity contracts, pushing air out.
  • Sneezing: Expels foreign particles (dust, pollen) trapped in the nasal cavity to ensure clean air enters the body.
6.4 What Do We Breathe Out?

Composition of Inhaled and Exhaled Air

  • Inhaled Air: 21% Oxygen, 0.04% Carbon Dioxide.
  • Exhaled Air: 16.4% Oxygen, 4.4% Carbon Dioxide.
  • Exhaled air contains moisture which condenses on cool surfaces (like a mirror).
  • Carbon dioxide in exhaled air turns lime water milky.
6.5 Respiration in Other Animals

Insects, Earthworms, and Frogs

  • Cockroach: Breathes through small lateral openings called spiracles connected to a network of air tubes called tracheae.
  • Earthworm: Exchanges gases directly through its moist, slimy skin.
  • Frogs: Possess lungs but can also breathe through their moist, slippery skin.
6.6 & 6.7 Underwater and Plant Respiration

Breathing Under Water

  • Fish: Use gills (richly supplied with blood vessels) to absorb oxygen dissolved in water.

Respiration in Plants

  • Plants take in oxygen and release carbon dioxide for cellular respiration.
  • Stomata: Tiny pores on leaves used for gas exchange.
  • Root Hairs: Absorb air from the spaces present between soil particles.