Ch.
5- LIFE PROCESSES (RESPIRATION)
Notes
Subject: Science (Biology) Grade: X
Definition of Respiration
Respiration is a catabolic process in which energy is released from simple carbohydrates like glucose. This energy is
stored in the form of ATP (Adenosine Triphosphate).
"Respiration is the step-wise oxidation of glucose inside the cells to release energy."
Why is Respiration Necessary?
• To provide energy for all biological processes like:
o Synthesis of proteins
o Cell division
o Movement
o Repair of cells
Types of Respiration
1. Aerobic Respiration
• Takes place in the presence of oxygen.
• Glucose is completely broken down into carbon dioxide and water.
• High energy yield (38 ATP).
Occurs in most plants and animals (including humans).
2. Anaerobic Respiration
• Takes place in the absence of oxygen.
• Glucose is partially broken down.
• Produces less energy (only 2 ATP per glucose).
Two examples:
• In yeast (Alcoholic fermentation):
• In human muscle cells (Lactic acid fermentation):
Lactic acid accumulation causes muscle fatigue and cramps during heavy exercise.
Three pathways for breakdown of glucose for release of energy-
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Key Differences: Aerobic vs Anaerobic Respiration
Feature Aerobic Respiration Anaerobic Respiration
Oxygen Requirement Present Absent
End Products CO₂ and H₂O Lactic acid / Alcohol and CO₂
Energy Produced 38 ATP 2 ATP
Occurs In Plants, animals (most cells) Yeast, muscle cells during exercise
Human Respiratory System: Structure and Function
1. Nostrils: Entry of air.
2. Nasal cavity: Filters (via hairs and mucus), moistens and warms air.
3. Pharynx: Common path for food and air.
4. Larynx (Voice box): Produces sound.
5. Trachea: Windpipe with cartilage rings to prevent collapse.
6. Bronchi: Two branches from trachea to lungs.
7. Bronchioles: Finer branches inside lungs.
8. Alveoli: Microscopic air sacs where gas exchange occurs.
Gaseous Exchange at Alveoli
• Oxygen from alveolar air diffuses into blood capillaries.
• Carbon dioxide from blood diffuses into alveolar space.
• Alveoli are suited for exchange due to:
o Large surface area
o Thin walls
o Moist surface
o Rich blood supply
Mechanism of Breathing
Process Action Effect
Inhalation Diaphragm contracts, rib cage lifts Thoracic cavity expands → air rushes in
Exhalation Diaphragm relaxes, rib cage lowers Thoracic cavity contracts → air pushed out
Common Misconceptions
• Respiration ≠ Breathing.
o Breathing is a physical process (inhaling and exhaling).
o Respiration is a chemical process (cellular breakdown of glucose).
Important Terms
• ATP: Main energy currency of the cell.
• Mitochondria: Site of aerobic respiration.
• Lactic acid: By-product of anaerobic respiration in muscles.
• Fermentation: Anaerobic respiration in microbes like yeast.
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