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NCERT Class 10 Science — Chapter 6

Life Processes

Autotrophic nutrition (photosynthesis), Heterotrophic digestion in human alimentary canal, Aerobic & Anaerobic respiration (glycolysis, lactic acid, ethanol), Human circulatory system (double circulation, heart, blood vessels), and Excretory system (nephron ultrafiltration, selective reabsorption, dialysis).

Quick Key Takeaways:
Photosynthesis Master Equation: 6CO2+12H2O→Chlorophyll, SunlightC6H12O6+6O2+6H2O6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow{\text{Chlorophyll, Sunlight}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 + 6\text{H}_2\text{O} Three steps: (1) Light absorption by chlorophyll, (2) Splitting of water (photolysis) & conversion of light energy to chemical energy (ATP, NADPH), (3) Reduction of CO2\text{CO}_2 to carbohydrates.
Breakdown of Glucose: Cytoplasm glycolysis produces Pyruvate (3-Carbon) →\rightarrow (1) Absence of O2\text{O}_2 in yeast →\rightarrow Ethanol + CO2\text{CO}_2 + 2 ATP; (2) Lack of O2\text{O}_2 in muscle cells →\rightarrow Lactic acid + 2 ATP (causes muscle cramps); (3) Presence of O2\text{O}_2 in mitochondria →\rightarrow 6CO2+6H2O+386\text{CO}_2 + 6\text{H}_2\text{O} + 38 ATP.
Double Circulation in Humans: Blood travels through the heart twice in one complete cycle: (1) Pulmonary Circulation (Right ventricle →\rightarrow Lungs →\rightarrow Left atrium), (2) Systemic Circulation (Left ventricle →\rightarrow Body tissues →\rightarrow Right atrium). Prevents mixing of oxygenated and deoxygenated blood.
Nephron Urine Formation: (1) Glomerular Ultrafiltration (water, glucose, amino acids, urea forced into Bowman's capsule), (2) Selective Tubular Reabsorption (glucose, amino acids, essential salts reabsorbed in PCT), (3) Tubular Secretion & collecting duct.
Jump to Concept:1. 1. Autotrophic & Heterotrophic Nutrition & Digestive System Mechanisms2. 2. Respiration, Double Circulation & Nephron Excretory Mechanisms3. 3. High-Yield Solved Board Examination Questions (3-Mark & 5-Mark)4. 4. Practical Laboratory & Competency-Based Case Drill: Starch Test & Destarching in Photosynthesis (NCERT Activity 6.1)5. 5. CBSE Examiner Marking Scheme, Scientific Notation & Deduction Traps
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1. Autotrophic & Heterotrophic Nutrition & Digestive System Mechanisms

Fundamental Principles

Core scientific laws, chemical equations, anatomical structures, and visual model for Life Processes.

• Human Digestive System: Step-by-Step Enzymatic Actions
•
1. Mouth / Buccal Cavity: Teeth chew food; Salivary Amylase (Ptyalin) hydrolyzes starch into maltose (simpler sugar) at neutral/slightly alkaline pH: Starch→Salivary AmylaseMaltose\text{Starch} \xrightarrow{\text{Salivary Amylase}} \text{Maltose}
•
2. Stomach: Gastric glands secrete Gastric Juice containing:
- Hydrochloric Acid (HCl\text{HCl}): Creates acidic pH (1.5−2.01.5-2.0) to activate pepsinogen into active Pepsin, and kills ingested bacteria.
- Pepsin: Breaks down complex proteins into peptones and proteoses.
- Mucus: Protects the inner stomach lining from acidic corrosion.
•
3. Small Intestine (Site of Complete Digestion):
- Bile Juice (from Liver): Contains no enzymes, but performs Emulsification (breaks large fat globules into tiny droplets) and makes acidic chyme alkaline.
- Pancreatic Juice (from Pancreas): Contains Trypsin (digests proteins into peptides) and Pancreatic Lipase (digests emulsified fats into fatty acids and glycerol).
- Intestinal Juice (Succus Entericus): Final conversion →\rightarrow Carbohydrates to Glucose, Proteins to Amino Acids, Fats to Fatty Acids + Glycerol.
•
4. Absorption via Villi: Finger-like projections in the ileum lined with rich capillary blood networks increase surface area for rapid nutrient absorption.
📊 Life Processes: Nephron Filtration & Circulatory PathwaysVisual Model
1. GLOMERULUSCapillaryBowman's CupUltrafiltration2. TUBULE (PCT)Loop of HenleSelective Reabsorp.3. COLLECTINGDuct SystemUrine FormationREABSORBED• Glucose• Amino Acids• Salts (NaCl)• Water (H₂O)Urea ExcretedRenal Artery → Afferent Arteriole → Glomerular Filtrate → Tubular Reabsorption → Ureter → Bladder

Visual schematic mapping the human nephron ultrafiltration stages, the 4-chambered heart double circulation, and the 3 glucose respiration pathways.

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2. Respiration, Double Circulation & Nephron Excretory Mechanisms

Mechanisms & Experiments

Step-by-step chemical reaction mechanisms, experimental activities, and physiological pathways for Life Processes.

• Respiratory Energy Pathways & The Human Heart Architecture
•
Alveoli Respiratory Surface: Millions of balloon-like alveoli provide massive surface area ( 80 m2~80\text{ m}^2) with ultra-thin walls and extensive capillary networks for gas diffusion (O2\text{O}_2 into blood, CO2\text{CO}_2 into alveolar air). Respiratory pigment Hemoglobin transports O2\text{O}_2.
•
Four-Chambered Human Heart:
- Left Atrium & Left Ventricle: Receive and pump oxygenated blood under high pressure to systemic organs through the thick-walled Aorta.
- Right Atrium & Right Ventricle: Receive deoxygenated blood from Vena Cava and pump it to lungs via Pulmonary Artery.
- Valves (Tricuspid, Bicuspid/Mitral, Semilunar): Ensure unidirectional flow and prevent backflow of blood.
•
Arteries vs Veins vs Capillaries:
- Arteries: Thick, elastic, muscular walls; no valves; carry blood away from heart under high pressure.
- Veins: Thin walls; large lumen; contain one-way valves; carry blood toward heart under low pressure.
- Capillaries: Single-cell-thick walls for direct interstitial nutrient and gas exchange.
• Nephron Structure & The Mechanics of Excretion
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Functional Unit of Kidney: Nephron consists of Bowman's Capsule, Glomerulus, Proximal Convoluted Tubule (PCT), Loop of Henle, Distal Convoluted Tubule (DCT), and Collecting Duct.
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Ultrafiltration: Blood enters through wide afferent arteriole into glomerulus knot at high pressure. Solutes (glucose, salts, urea, water) filter across semi-permeable membrane into Bowman's capsule as primary filtrate (~180 liters/day).
•
Selective Reabsorption: As filtrate flows along PCT, ~99% of water, all glucose, and amino acids are actively reabsorbed back into peritubular capillaries. Only ~1.5 liters of concentrated urine (containing urea, uric acid, excess salts) is excreted daily.
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3. High-Yield Solved Board Examination Questions (3-Mark & 5-Mark)

Solved Board Questions

Standard CBSE board exam questions with complete scientific justifications and marking scheme step protocols.

• 3-Mark Standard Board Question: Why is double circulation necessary in human beings? Explain the flow of blood through the four chambers of the heart.
•
Necessity of Double Circulation:
1. Complete physical separation of oxygenated and deoxygenated blood prevents mixing.
2. Ensures a highly efficient, high-pressure supply of oxygen to body cells, which is essential to maintain high metabolic activity and constant body temperature (warm-blooded homeothermy).
•
Step-by-Step Flow Pathway:
1. Oxygenated blood from lungs travels via Pulmonary Veins →\rightarrow Left Atrium.
2. Left Atrium contracts, pushing blood through bicuspid valve into the thick muscular Left Ventricle.
3. Left Ventricle contracts forcefully, pumping blood through the Aorta to all body tissues (Systemic Circulation).
4. Deoxygenated blood from body tissues returns via Vena Cava →\rightarrow Right Atrium.
5. Right Atrium contracts, passing blood through tricuspid valve into the Right Ventricle.
6. Right Ventricle pumps deoxygenated blood via Pulmonary Artery to the lungs for oxygenation (Pulmonary Circulation).
• 5-Mark Comprehensive Question / Numerical: (a) Draw a neat, labelled diagram of a Nephron and describe the three steps involved in urine formation.
(b) Differentiate between Aerobic and Anaerobic Respiration with energy yields and end products.
•
Part (a) Urine Formation in Nephron:
1. Glomerular Filtration: High hydrostatic pressure in the glomerulus forces water, glucose, amino acids, mineral ions, and nitrogenous waste (urea) out of blood capillaries into Bowman's capsule.
2. Selective Tubular Reabsorption: Useful substances like glucose, amino acids, major electrolytes (Na+,K+\text{Na}^+, \text{K}^+), and large volume of water are selectively reabsorbed by active transport across PCT cells into adjacent blood capillaries.
3. Tubular Secretion: Excess potassium ions, hydrogen ions, and drugs are actively secreted from peritubular capillaries into the tubular lumen to maintain ionic balance and blood pH, forming final urine that enters the collecting duct.
•
Part (b) Comparison of Aerobic vs Anaerobic Respiration:
- Site of Reaction: Aerobic occurs in Cytoplasm + Mitochondria; Anaerobic occurs strictly in Cytoplasm.
- Oxygen Requirement: Aerobic requires molecular O2\text{O}_2; Anaerobic takes place in the absence of O2\text{O}_2.
- End Products: Aerobic yields CO2+H2O\text{CO}_2 + \text{H}_2\text{O}; Anaerobic yields Ethanol + CO2\text{CO}_2 (in yeast) or Lactic Acid (in muscle cells).
- Energy Yield: Aerobic yields 38 ATP (high energy); Anaerobic yields only 2 ATP (low energy).
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4. Practical Laboratory & Competency-Based Case Drill: Starch Test & Destarching in Photosynthesis (NCERT Activity 6.1)

Practical & Case Drill

Experimental observation analysis, chemical gas tests, and assertion-reason drills.

• Laboratory Activity Context: Starch Test & Destarching in Photosynthesis (NCERT Activity 6.1)
A potted plant with variegated leaves (e.g. Money plant or Croton) is kept in a dark room for three days to destarch, then exposed to sunlight for 6 hours, followed by boiling in alcohol and iodine staining.
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Q1: Why is the plant kept in the dark for three days before the experiment? →\rightarrow To completely destarch the leaves (all stored starch is consumed by respiration in the absence of photosynthesis).
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Q2: Why is the leaf boiled in an alcohol water bath? →\rightarrow Alcohol dissolves and extracts the green chlorophyll pigment, bleaching the leaf white so that iodine colour changes can be seen clearly.
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Q3: What observation is recorded after adding iodine solution? →\rightarrow Only the originally green regions containing chlorophyll turn blue-black with iodine, proving that chlorophyll is strictly essential for photosynthesis.
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5. CBSE Examiner Marking Scheme, Scientific Notation & Deduction Traps

Important Solved Board Questions

Examiner step-marking allocations, mandatory scientific terminology, and common error avoidance.

• Step-by-Step Marking Rubric & Key Terminology
•
1 Mark: Complete balanced chemical equation for photosynthesis.
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1 Mark: Step-by-step description of three glucose breakdown pathways with ATP counts.
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2 Marks: Systematic blood circulation sequence naming all 4 heart chambers and vessels.
•
1 Mark: Nephron ultrafiltration vs selective reabsorption distinction.
• Common Error Deduction Traps
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Trap 1: Confusing pulmonary artery (carries deoxygenated blood to lungs) with pulmonary vein (carries oxygenated blood to heart).
•
Trap 2: Forgetting that bile contains NO digestive enzymes (its function is mechanical emulsification and alkalization).
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Trap 3: Confusing the site of anaerobic respiration (muscle produces lactic acid; yeast fermentation produces ethanol + CO2\text{CO}_2).
Authentic Board Question (5 Marks)Topic: Human Circulatory System
Describe the complete mechanism of double circulation in human beings with the help of a schematic flow diagram. Why is it necessary in birds and mammals?

Official CBSE Step-by-Step Marking Breakdown:

Step 1: Pulmonary Circulation: Deoxygenated blood from Right Ventricle →\to Pulmonary Artery →\to Lungs →\to Oxygenated blood →\to Pulmonary Veins →\to Left Atrium.
1½ Marks
Step 2: Systemic Circulation: Oxygenated blood from Left Ventricle →\to Aorta →\to Body Organs →\to Deoxygenated blood →\to Vena Cava →\to Right Atrium.
1½ Marks
Step 3: Schematic Flow Chart: Clean box/arrow diagram connecting Heart, Lungs, and Body Tissues.
1 Mark
Step 4: Biological Necessity: Separation prevents mixing of oxygenated & deoxygenated blood, providing high energy required to maintain constant body temperature (warm-blooded / homeothermy).
1 Mark
Model Student Answer (Target: Full 5/5 Marks):
Double Circulation Mechanism:
Blood travels through the human heart twice during each complete cycle of the body.

1. Pulmonary Circulation (Heart ↔\leftrightarrow Lungs):
- Deoxygenated blood collected from body tissues enters the Right Atrium →\to pumped into Right Ventricle.
- Right ventricle pumps it to the Lungs via Pulmonary Artery for oxygenation.
- Oxygenated blood returns to the Left Atrium via Pulmonary Veins.

2. Systemic Circulation (Heart ↔\leftrightarrow Body Tissues):
- Oxygenated blood passes from Left Atrium →\to Left Ventricle.
- Left ventricle vigorously pumps blood into Aorta, distributing it to all body organs.
- Deoxygenated blood from tissues is returned to Right Atrium via Vena Cava.

Necessity in Birds and Mammals:
Birds and mammals are warm-blooded (endothermic) animals that constantly require high energy to maintain a constant body temperature. Separation of oxygenated and deoxygenated blood ensures highly efficient oxygen delivery to cellular tissues without any dilution.
Examiner Mark Deduction Traps:
•Remember that Pulmonary Artery carries DEOXYGENATED blood and Pulmonary Vein carries OXYGENATED blood (exceptions to standard vessels).
•Mentioning "homeothermy / constant body temperature" is mandatory for the final mark.

High-Frequency Conceptual Doubts & FAQs

Curated answers to the most common questions asked by Class 10 students.
1. HCl: Creates an acidic pH\text{pH} (approx1.5−2approx 1.5 - 2) essential for activating pepsinogen into active pepsin and kills ingested harmful bacteria.
2. Pepsin: An enzyme that breaks down complex proteins into smaller peptides/peptones in the acidic environment.
3. Mucus: Secreted by goblet cells to form a protective barrier on the inner stomach lining, preventing corrosion from concentrated HCl\text{HCl}.

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