Chapter 10: Respiration in Organisms
जीवों में श्वसन (सेलुलर श्वसन, डायाफ्राम गति एवं अन्य जीवों में श्वसन)
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- Cellular Respiration: The process of breakdown of food (glucose) in cells with the release of energy.
- Aerobic vs Anaerobic Respiration: Aerobic takes place in the presence of oxygen producing CO2, water, and 36-38 ATP; Anaerobic occurs without oxygen (yeast produces ethanol + CO2 + energy, used in brewing and baking).
- Muscle Cramps during vigorous exercise: Anaerobic breakdown of glucose in human muscle cells produces Lactic Acid. Accumulation of lactic acid causes painful cramps. Relieved by a hot water bath or gentle massage which improves blood circulation and oxygen supply.
- Breathing Mechanism in Humans: Inhalation (ribs move UP and OUT, diaphragm moves DOWN/contracts and flattens, chest cavity increases in volume, air rushes in). Exhalation (ribs move DOWN and IN, diaphragm moves UP/relaxes into a dome shape, chest volume decreases, air is pushed out).
- Gas composition: Inhaled air contains 21% Oxygen and 0.04% Carbon Dioxide; Exhaled air contains ~16.4% Oxygen and ~4.4% Carbon Dioxide.
- Respiration in other organisms: Earthworm breathes through moist, slimy skin (cutaneous); Cockroaches/insects breathe via spiracles (lateral pores) and a network of tracheae; Fish breathe through vascular gills with thin filaments; Frogs breathe through moist skin in water and lungs on land; Plants take up oxygen through leaf stomata and roots through air spaces in soil.
- Trap: CBSE asks what causes muscle cramps during intense sprinting. Correct: Accumulation of LACTIC ACID (not ethanol, not CO2).
- Trap: CBSE asks diaphragm movement during inhalation. Correct: Diaphragm moves DOWNWARDS (flattens) and ribs move UP and OUT.
- Trap: CBSE claims earthworms breathe through lungs or tracheae. Correct: Earthworms breathe through MOIST SKIN.
NCERT Core Facts: Respiration & Biomechanical Gas Exchange
In CTET Paper 2 Science, questions on respiration pathways, human respiratory biomechanics, and diverse animal adaptations appear consistently.
1. Cellular Respiration: Chemical Pathways
- Aerobic Respiration (Presence of $O_2$):
- Anaerobic Respiration in Yeast (Fermentation):
- Application: Single-celled fungi (yeast) respire anaerobically; the liberated CO_2 causes dough to rise in bread baking, and ethanol is used in brewing wine and beer.
- Anaerobic Respiration in Human Muscle Cells:
- During vigorous sprinting or cycling, oxygen demand outstrips supply. Muscle cells respire anaerobically, producing lactic acid.
- Relief: A hot water bath or deep massage enhances blood flow, restoring oxygen to fully oxidize lactic acid into CO_2 and H_2O.
2. Biomechanics of Human Breathing
| Respiratory Phase | Rib Cage Movement | Diaphragm Movement | Thoracic Cavity Volume | Air Flow |
|---|---|---|---|---|
| Inhalation (अंतःश्वसन) | Moves Up and Out | Moves Down (Flattens) | Increases | Air rushes into lungs |
| Exhalation (उच्छ्वसन) | Moves Down and In | Moves Up (Dome-shaped) | Decreases | Air forced out of lungs |
Air Composition Comparison
- Inhaled Air: 21\% \text{ Oxygen } (O_2) and 0.04\% \text{ Carbon Dioxide } (CO_2).
- Exhaled Air: 16.4\% \text{ Oxygen } (O_2) and 4.4\% \text{ Carbon Dioxide } (CO_2).
3. Respiration Across Diverse Organisms
- Earthworms (केंचुआ): Breathe through their moist and slimy skin. Gases diffuse directly across the thin cuticle into epidermal blood capillaries.
- Insects / Cockroach (तिलचट्टा): Air enters through tiny lateral pores called spiracles and circulates through a network of internal air tubes called tracheae. Blood in insects does not carry oxygen (it lacks hemoglobin).
- Fish (मछली): Breathe through gills (गलफड़े) covered by an operculum. Water enters the mouth and flows over richly vascularized gill filaments, where dissolved oxygen diffuses into the blood.
- Frogs (मेंढक): Have dual respiratory organs: moist skin under water and lungs on land.
- Plants: Gas exchange occurs via stomata on leaves and lenticels on woody stems. Roots absorb oxygen present in microscopic air spaces between soil particles.
Test Your Mastery: Respiration in Organisms
Authentic CBSE exam questions tested directly from this NCERT chapter.
During heavy physical exercise, accumulation of which chemical substance leads to muscle cramps?
अत्यधिक शारीरिक व्यायाम के दौरान किस रासायनिक पदार्थ के संचय से मांसपेशियों में ऐंठन (cramps) होती है?
During the process of inhalation in human respiration, the ribs move:
मानव श्वसन में अंतःश्वसन (inhalation) की प्रक्रिया के दौरान पसलियाँ (ribs) गति करती हैं:
A student observes a cockroach and notes its respiratory system. Which of the following organs are responsible for gas exchange in insects?
एक छात्र तिलचट्टे का अवलोकन करता है। कीटों में गैसों के विनिमय के लिए कौन-से अंग उत्तरदायी हैं?
Why do muscle cramps occur after heavy exercise?
Due to the partial breakdown of glucose producing lactic acid when oxygen supply is insufficient in muscle cells.
How do earthworms breathe according to NCERT Class 7 Science?
Earthworms breathe through their moist and slimy skin through direct cutaneous diffusion.
What happens to the diaphragm during inhalation?
The diaphragm contracts and moves downward (flattens), increasing the thoracic volume.