Chapter 6:
Respiration in Organisms

Class 7 Science | CBSE Curriculum

Learn aerobic and anaerobic respiration, breathing mechanism, human respiratory system, breathing in insects, fish, earthworms, plants, and muscle cramps explained with questions and activities.

Score:
0
Time:
05:00

Quick Revision: Respiration in Organisms

  • Cellular Respiration: Breakdown of food in cells to release energy. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (aerobic).
  • Aerobic Respiration: Uses oxygen, produces CO₂ + water + large energy (36-38 ATP).
  • Anaerobic Respiration: No oxygen, produces lactic acid (muscles) or alcohol + CO₂ (yeast), less energy (2 ATP).
  • Breathing Rate: Normal adult: 15-18 breaths/min; increases with exercise.
  • Inhalation: Ribs move up/out, diaphragm down → chest cavity increases → air rushes in.
  • Exhalation: Ribs move down/in, diaphragm up → chest cavity decreases → air pushed out.
  • Human Respiratory Organs: Nostrils → nasal cavity → trachea → bronchi → bronchioles → alveoli (lungs).
  • Insect Respiration: Spiracles → tracheae (air tubes) → direct to cells.
  • Fish Respiration: Gills extract dissolved oxygen from water.
  • Earthworm & Frog: Breathe through moist skin (cutaneous respiration); frog also has lungs.
  • Plant Respiration: Through stomata (leaves) and root hair (air spaces in soil).
  • Muscle Cramps: Caused by lactic acid buildup during anaerobic respiration; relieved by massage/hot bath (improves circulation).

Chapter Summary:

Respiration in Organisms explains the vital process by which living beings obtain energy from food. The chapter distinguishes between aerobic respiration (with oxygen, high energy yield) and anaerobic respiration (without oxygen, lower energy yield). It details the mechanism of breathing in humans, including the roles of the ribs, diaphragm, and lungs. The concept of breathing rate and its variation with physical activity is explored through activities. The chapter also covers diverse respiratory structures across organisms: spiracles and tracheae in insects, gills in fish, moist skin in earthworms and frogs, and stomata in plants. Key topics include the cause of muscle cramps (lactic acid accumulation), the effect of exercise on breathing, and why mountaineers carry oxygen cylinders. The chapter emphasizes that respiration is a continuous, energy-releasing process essential for all life functions.

Practical applications include understanding why we sneeze, how to measure chest expansion, and the dangers of smoking. The chapter also introduces models (e.g., bottle and balloon) to simulate breathing mechanics. By the end, students appreciate the unity of life: despite different organs, all organisms respire to release energy from glucose.