Class 7 Science Notes Chapter 10 (Respiration in Organisms) – Science Book

Okay, let's prepare detailed notes for Chapter 10: Respiration in Organisms, focusing on aspects relevant for government exam preparation based on NCERT Class 7 Science.

Chapter 10: Respiration in Organisms - Key Concepts & Notes

1. Why Do We Respire?

• Energy Requirement: All living organisms (plants, animals, microbes) are made of microscopic units called cells. Cells perform various functions like nutrition, transport, excretion, and reproduction. To perform these functions, cells require energy.
• Source of Energy: The food we eat contains stored energy.
• Respiration: The process of breaking down food (primarily glucose) in the cells with the release of energy is called respiration. It occurs inside the cells of all organisms.
  • Therefore, it is also called Cellular Respiration.

2. Cellular Respiration: The Process

• Location: Takes place inside the cytoplasm and mitochondria of the cell.
• Reactants: Glucose (from food) and Oxygen (usually).
• Products: Carbon Dioxide, Water, and Energy.
• Equation (Simplified Word Equation):
  Glucose (Food) → [in the presence of Oxygen] → Carbon Dioxide + Water + Energy

3. Types of Respiration

• a) Aerobic Respiration:

  • Definition: Breakdown of glucose occurs in the presence of oxygen.
  • Equation: Glucose → (with the use of Oxygen) → Carbon Dioxide + Water + Large amount of Energy
  • Occurrence: Happens in most organisms, including humans, animals, and plants, when oxygen is sufficiently available.

• b) Anaerobic Respiration:

  • Definition: Breakdown of food occurs in the absence of oxygen.
  • Occurrence:
    • Anaerobes: Organisms like yeast can survive without air (oxygen). They respire anaerobically.
    • Equation (in Yeast): Glucose → (in the absence of Oxygen) → Alcohol + Carbon Dioxide + Less Energy
    • Application: Yeast is used in making wine and beer due to alcohol production through anaerobic respiration (fermentation).
    • Muscle Cells (Temporary): Our muscle cells can also respire anaerobically for a short time during heavy exercise (fast running, cycling, weight lifting) when the demand for energy is high, but the supply of oxygen is limited.
    • Equation (in Muscle Cells): Glucose → (in the absence of Oxygen) → Lactic Acid + Less Energy
    • Effect: Accumulation of lactic acid in muscles causes muscle cramps. Relief is obtained by a hot water bath or massage, which improves blood circulation, increasing oxygen supply to the cells, leading to the complete breakdown of lactic acid into CO2 and water.

Key Difference: Aerobic vs. Anaerobic Respiration

4. Breathing (External Respiration)

• Definition: The mechanism by which organisms take in oxygen-rich air from the environment and release carbon dioxide-rich air. It is the process of gas exchange.
• Relation to Cellular Respiration: Breathing provides the oxygen required for aerobic cellular respiration and removes the carbon dioxide produced during it.
• Two Steps:
  • Inhalation: Taking in air rich in oxygen.
  • Exhalation: Giving out air rich in carbon dioxide.
• Breathing Rate: The number of times a person breathes in one minute.
  • One breath = One inhalation + One exhalation.
  • Normal Rate (Adult at Rest): 15-18 times per minute.
  • Effect of Exercise: Breathing rate increases during physical activity to supply more oxygen to cells for increased energy demand. We breathe faster and deeper.

5. Mechanism of Breathing in Humans

• Respiratory System Organs: Nostrils → Nasal Cavity → Windpipe (Trachea) → Bronchi → Lungs (located in the chest cavity).

• Chest Cavity: Surrounded by ribs on the sides and a large muscular sheet called the diaphragm at the base.

• Process:

  • During Inhalation:
    • Ribs move up and outwards.
    • Diaphragm moves down.
    • This increases the volume (space) in the chest cavity.
    • Air pressure inside decreases, and air rushes into the lungs.
  • During Exhalation:
    • Ribs move down and inwards.
    • Diaphragm moves up to its original position.
    • This decreases the volume of the chest cavity.
    • Air pressure inside increases, and air is pushed out of the lungs.

• Composition of Inhaled and Exhaled Air:

  • Inhaled Air: Approx. 21% Oxygen, 0.04% Carbon Dioxide.
  • Exhaled Air: Approx. 16.4% Oxygen, 4.4% Carbon Dioxide. (Nitrogen percentage remains largely unchanged).
  • Key takeaway: Exhaled air has less oxygen and significantly more carbon dioxide than inhaled air.

6. Breathing in Other Animals

• Cockroach (and other Insects):
  • Have small openings called spiracles on the sides of their body.
  • Spiracles connect to a network of air tubes called tracheae that branch throughout the body.
  • Air enters through spiracles, travels through tracheae, and reaches body tissues directly for gas exchange. Blood does not play a major role in gas transport in insects.
• Earthworm:
  • Breathe through their moist and slimy skin (Cutaneous Respiration).
  • Gases can easily pass through the thin, moist skin directly into the blood capillaries underneath.
• Fish:
  • Have gills as respiratory organs.
  • Gills are projections of the skin, well supplied with blood vessels.
  • Fish take in water through their mouth, which then flows over the gills.
  • Gills extract dissolved oxygen from the water, and carbon dioxide is released into the water.

7. Respiration in Plants

• Process: Plants also respire like other living organisms; they take in oxygen from the air and give out carbon dioxide. This provides energy for their cellular activities.
• Gas Exchange Organs:
  • Leaves: Have tiny pores called stomata (singular: stoma) for the exchange of oxygen and carbon dioxide.
  • Stems: Woody stems have lenticels for gas exchange. Herbaceous stems may have stomata.
  • Roots: Root cells take up oxygen from the air spaces present between soil particles via root hairs.
• Important Note: Respiration in plants occurs day and night. Photosynthesis (using CO2, releasing O2) occurs only during the day in the presence of sunlight. While plants release O2 during photosynthesis, they consume O2 during respiration continuously.
• Independent Respiration: Each part of the plant (roots, stem, leaves) can independently take in oxygen and give out carbon dioxide.

Summary Points for Quick Revision:

• Respiration releases energy from food within cells (Cellular Respiration).
• Aerobic respiration uses oxygen and yields more energy.
• Anaerobic respiration occurs without oxygen, yields less energy, producing alcohol (yeast) or lactic acid (muscles).
• Breathing is the mechanical process of taking in O2 and releasing CO2.
• Human breathing involves ribs and diaphragm movement changing chest cavity volume.
• Breathing rate increases with physical activity.
• Insects use spiracles and tracheae.
• Earthworms use moist skin.
• Fish use gills to extract dissolved oxygen from water.
• Plants respire through stomata, lenticels, and root hairs, taking in O2 and releasing CO2 continuously.

This covers the essential points from NCERT Class 7, Chapter 10, structured for exam preparation. Remember to focus on definitions, differences (like aerobic vs anaerobic, breathing vs respiration), mechanisms, and examples across different organisms.