🌿 CHAPTER: Respiration and Excretion (Pages 53–78) — SCERT Kerala Class 9 Biology (2024 Edition)

 

🌿 CHAPTER: Respiration and Excretion (Pages 53–78)

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🔹 CAPSULE NOTES (Summary)

• Respiration is the process of breaking down glucose using oxygen to release energy in cells.

• Respiratory system in humans includes nasal cavity, trachea, bronchi, lungs, and alveoli.

• Alveoli are the sites of gas exchange — oxygen enters the blood and carbon dioxide leaves it.

• Cellular respiration occurs in two stages:

  1. Glycolysis (in cytoplasm, no oxygen, 2 ATP).

  2. Krebs Cycle (in mitochondria, uses oxygen, 28 ATP).

• Excretion removes metabolic wastes like urea, carbon dioxide, and salts.

• Kidneys filter waste from blood through nephrons (basic structural unit).

• Urine formation involves:

  1. Filtration in Bowman’s capsule

  2. Reabsorption in tubules

  3. Secretion of wastes into collecting ducts

• Excretion in plants: via stomata, lenticels, hydathodes, and leaf fall.

• Homeostasis maintains internal balance by kidney, lungs, liver, and skin.

• Hemodialysis and kidney transplantation help patients with kidney failure.

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💡 POINTS TO REMEMBER

• Respiration ≠ Breathing; it includes both gas exchange and cellular energy release.

• Lavoisier proved that respiration is similar to burning.

• Ventilation = Inspiration (inhaling) + Expiration (exhaling).

• Haemoglobin carries oxygen; low levels cause anaemia.

• Excretory organs:

  • Kidney → urine (water, salts, urea)

  • Lungs → CO₂, water vapor

  • Skin → sweat

  • Liver → urea synthesis

• Urea synthesis occurs in the liver from ammonia (toxic).

• Homeostasis keeps temperature, pH, and fluid levels balanced.

• Proper hydration and timely urination are essential for kidney health.

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🧠 IMPORTANT DEFINITIONS (Short & Exam-Focused)

Term	Definition
Respiration	The process of breaking down glucose using oxygen to release energy.
Ventilation	The movement of air into and out of lungs (breathing).
Alveoli	Tiny air sacs in lungs where gas exchange occurs.
Glycolysis	First stage of respiration (in cytoplasm, 2 ATP formed).
Krebs Cycle	Second stage of respiration (in mitochondria, 28 ATP formed).
Excretion	Removal of metabolic wastes from the body.
Nephron	Functional unit of kidney that filters blood.
Urea	A less toxic nitrogenous waste formed from ammonia in liver.
Hemodialysis	Artificial removal of wastes from blood when kidneys fail.
Homeostasis	Maintenance of stable internal environment in the body.
Pleura	Membrane covering the lungs.
Diaphragm	Muscular wall separating chest and abdomen, aids breathing.
Surfactant	Substance that prevents alveoli from collapsing.
Anaerobic respiration	Respiration without oxygen (e.g., yeast, muscle cells).

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📝 ONE-WORD QUESTIONS

1. Scientist who explained respiration similar to burning – Lavoisier

2. Air sacs in lungs – Alveoli

3. Site of glycolysis – Cytoplasm

4. Site of Krebs cycle – Mitochondria

5. Functional unit of kidney – Nephron

6. Organ that forms urea – Liver

7. Gas released during respiration – Carbon dioxide

8. Blood vessel that carries urine from kidney – Ureter

9. Outer part of kidney – Cortex

10. Process maintaining internal balance – Homeostasis

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💬 ONE/TWO-SENTENCE QUESTIONS & ANSWERS

1. What is respiration?
   Respiration is the process in which glucose is broken down using oxygen to release energy, carbon dioxide, and water.

2. What is the function of alveoli?
   They provide a large moist surface for the exchange of oxygen and carbon dioxide between air and blood.

3. What is cellular respiration?
   The process by which cells break down glucose and produce energy in the form of ATP.

4. Differentiate between aerobic and anaerobic respiration.
   Aerobic uses oxygen (produces 30 ATP), while anaerobic occurs without oxygen (produces 2 ATP).

5. What is excretion?
   The process of removing waste materials formed during metabolism from the body.

6. Name the main excretory organs in humans.
   Kidneys, lungs, liver, and skin.

7. What is the role of nephron?
   Nephrons filter blood, reabsorb useful substances, and remove wastes as urine.

8. What is hemodialysis?
   A process where waste materials are removed from the blood using a dialysis machine when kidneys fail.

9. What is urea synthesis?
   Conversion of toxic ammonia into less toxic urea in the liver.

10. How is homeostasis maintained?
    By the coordinated functions of organs like kidneys, lungs, liver, and skin regulating body conditions.

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🧾 IMPORTANT FORMULAS & PROCESSES

1. Respiration Equation:
   Glucose + O₂ → CO₂ + H₂O + Energy (ATP)

2. Urea Formation (Simplified):
   Ammonia + CO₂ + H₂O → Urea + H₂O

3. Stages of Urine Formation:

   • Filtration → in Bowman’s capsule

   • Reabsorption → in tubules

   • Secretion → into collecting duct

4. Path of Air:
   Nostrils → Pharynx → Trachea → Bronchi → Bronchioles → Alveoli

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🧩 EXTRA QUICK RECALL

• Human lungs have about 70 crore alveoli (surface area ≈ 70 m²).

• Haemoglobin in RBC binds to oxygen forming oxyhaemoglobin.

• Anaerobic respiration in yeast produces alcohol and CO₂.

• Kidneys contain about 12 lakh nephrons each.

• Benedict’s test detects glucose in urine (changes from blue to red).

• Dialysis fluid removes waste by diffusion.

• Healthy kidneys regulate water, salts, and pH balance.

  
  

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  🔸 EXTENDED CAPSULE NOTES

  🔹 1. Human Respiratory System

  • Respiration = Breathing + Cellular respiration.

  • Breathing (Ventilation): Exchange of air between lungs and atmosphere.

  • Respiratory organs:
    Nasal cavity → Pharynx → Trachea → Bronchi → Bronchioles → Alveoli

  • Lungs:

    • Covered by pleural membrane

    • Protected by ribs and sternum

    • Separated from abdomen by diaphragm

  • Alveoli:

    • 70 crore alveoli in both lungs.

    • Walls are single-layered and moist for easy diffusion.

    • Surrounded by capillaries for gas exchange.

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  🔹 2. Mechanism of Breathing (Ventilation)

  Process	Muscles	Diaphragm	Rib Movement	Air Pressure	Air Movement
  Inhalation	Contracts	Moves down	Ribs move up/out	Decreases	Air enters lungs
  Exhalation	Relaxes	Moves up	Ribs move down/in	Increases	Air leaves lungs

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  🔹 3. Exchange of Gases (Alveolar Exchange)

  • Oxygen diffuses from alveoli → blood,
    CO₂ diffuses from blood → alveoli.

  • Moisture in alveolar walls helps gas dissolve and diffuse easily.

  • Surfactant prevents alveoli from collapsing during breathing.

  • The distance between alveolus and capillary wall is extremely small → efficient diffusion.

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  🔹 4. Transport of Gases

  • Oxygen Transport:

    • 97% by haemoglobin as oxyhaemoglobin

    • 3% dissolved in plasma

  • Carbon Dioxide Transport:

    • 7% dissolved in plasma

    • 23% as carbaminohaemoglobin

    • 70% as bicarbonate in blood

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  🔹 5. Cellular Respiration

  Phase	Location	Oxygen Use	End Products	ATP Produced
  Glycolysis	Cytoplasm	No	Pyruvic acid	2 ATP
  Krebs Cycle	Mitochondria	Yes	CO₂ + H₂O	28 ATP
  Total	—	—	—	30 ATP

  Equation:
  Glucose + O₂ → CO₂ + H₂O + Energy (ATP)

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  🔹 6. Respiration in Other Organisms

  Organism	Respiratory Surface	Type of Respiration
  Amoeba	Cell membrane	Diffusion
  Earthworm	Moist skin	Diffusion
  Fish	Gills	Aerobic
  Plants	Stomata, lenticels, roots	Aerobic
  Yeast	Cell cytoplasm	Anaerobic

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  🔹 7. Anaerobic Respiration

  • Without oxygen

  • Produces less energy (2 ATP)

  • In Yeast:
    Glucose → Alcohol + CO₂ + Energy

  • In Muscles (During heavy exercise):
    Glucose → Lactic acid + Energy (causes muscle fatigue)

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  🔹 8. Excretion in Humans

  • Main excretory organ: Kidney

  • Accessory organs: Skin, Lungs, Liver

  Organs and Waste Products

  Organ	Waste Removed
  Kidneys	Urea, salts, water
  Lungs	CO₂, water vapour
  Liver	Urea, bile pigments
  Skin	Sweat (water + salts + urea)

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  🔹 9. Structure of Nephron

  Parts & Functions:

  1. Bowman’s Capsule – filters blood from glomerulus.

  2. Glomerulus – cluster of capillaries for filtration.

  3. Tubules – reabsorb water, glucose, ions.

  4. Collecting Duct – collects urine from nephrons.

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  🔹 10. Formation of Urine

  1. Filtration:
     Blood filtered in glomerulus → filtrate in Bowman’s capsule.

  2. Reabsorption:
     Useful substances reabsorbed in tubules (glucose, water).

  3. Secretion:
     Extra wastes like drugs, salts secreted into tubules.

  Final urine = Filtrate – Reabsorbed substances + Secreted wastes.

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  🔹 11. Urea Synthesis

  • Occurs in Liver

  • Converts toxic ammonia → urea

  • Urea is excreted by kidneys in urine.

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  🔹 12. Excretion in Plants

  Process	Description
  Transpiration	Loss of water through stomata.
  Diffusion	CO₂, O₂ exchange via stomata & lenticels.
  Leaf Fall	Wastes stored in leaves shed off.
  Gum & Resin Formation	Wastes stored as harmless substances.

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  🔹 13. Artificial Methods of Excretion

  • Hemodialysis:

    • Artificial filtering of blood through dialysis machine.

    • Removes urea, salts, and excess water.

  • Kidney Transplantation:

    • Replacement of failed kidney with a healthy donor kidney.

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  🔹 14. Homeostasis

  • Maintaining stable internal environment (temperature, pH, water balance).

  • Organs involved: Kidney, liver, lungs, skin.

  • Importance: Essential for smooth metabolism and life processes.

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  🔹 MORE ONE-WORD QUESTIONS

  Question	Answer
  Site of gaseous exchange	Alveoli
  Gas required for respiration	Oxygen
  Gas produced during respiration	Carbon dioxide
  Number of ATP from one glucose	30 ATP
  Functional unit of kidney	Nephron
  Toxic nitrogenous waste	Ammonia
  Less toxic form of ammonia	Urea
  Site of urea synthesis	Liver
  Fluid filtered from glomerulus	Filtrate
  Organelle for energy production	Mitochondria
  Structure filtering blood	Glomerulus
  Protective covering of lungs	Pleura
  Movement of air	Ventilation
  Main excretory system	Urinary system
  Process of maintaining body balance	Homeostasis

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  🔹 TWO-SENTENCE QUESTIONS & ANSWERS

  1. Why is respiration important?
     Respiration releases energy stored in glucose molecules, necessary for body activities and growth.

  2. Differentiate between breathing and respiration.
     Breathing is physical movement of air; respiration is chemical breakdown of glucose to release energy.

  3. What is the function of the diaphragm in breathing?
     The diaphragm contracts during inhalation (air enters) and relaxes during exhalation (air goes out).

  4. Why is moist surface necessary for gas exchange?
     Moisture helps gases dissolve and diffuse quickly across membranes.

  5. What is the role of haemoglobin in respiration?
     It carries oxygen from lungs to tissues and carbon dioxide from tissues to lungs.

  6. How does anaerobic respiration in yeast help humans?
     It helps in baking (CO₂ makes dough rise) and brewing (alcohol formation).

  7. What happens if kidneys fail?
     Wastes accumulate in blood; artificial methods like dialysis are needed.

  8. What are the functions of skin in excretion?
     Removes urea, salts, and regulates body temperature through sweating.

  9. Why is homeostasis necessary?
     It keeps internal conditions constant for enzymes and metabolism to function properly.

  10. What is the difference between urea and urine?
      Urea is a waste product; urine is the fluid excreted containing urea, salts, and water.

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  🔹 EXTRA SHORT NOTES (Exam Boost)

  • Oxygen enters blood → forms oxyhaemoglobin → dissociates in tissues → energy release.

  • CO₂ formed in cells → enters blood → reaches lungs → exhaled.

  • Dialysis fluid is isotonic to blood, allowing only wastes to diffuse out.

  • Kidneys regulate: Water level, salt balance, pH.

  • Healthy kidney tip: Drink plenty of water and avoid excess salt and junk food.

  • Respiration rate increases during exercise due to higher oxygen demand.