Class 10th Science Chapter 5 – Life Processes | Human Respiratory System and Exchange of Gases

Life Processes – Human Respiratory System

Class 10 Science | Human Respiratory System and Exchange of Gases | CBSE + Foundation + Competitive

Human Respiratory System and Exchange of Gases

1. Human Respiratory System क्या है?

English:
The human respiratory system is the organ system responsible for taking oxygen into the body and removing carbon dioxide.

हिन्दी:
मानव श्वसन तंत्र वह अंग-तंत्र है जो शरीर में oxygen लेने तथा carbon dioxide को बाहर निकालने का कार्य करता है।

Respiratory system के प्रमुख अंग हैं:

• Nostrils – नासाछिद्र
• Nasal cavity – नासिका गुहा
• Pharynx – ग्रसनी
• Larynx – स्वरयंत्र
• Trachea – श्वासनली
• Bronchi – श्वसनी
• Bronchioles – श्वसनिकाएँ
• Alveoli – वायुकोष
• Lungs – फेफड़े
• Diaphragm – मध्यपट

2. 🫁 Animated Human Respiratory System Diagram

Human Respiratory System – Breathing & Air Flow

Animation: फेफड़ों का फैलना और सिकुड़ना breathing movement को दर्शाता है तथा नीले particles oxygen-rich air के flow को दर्शाते हैं।

3. Air का मार्ग | Pathway of Air

Nostrils → Nasal Cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

याद रखने का क्रम:
नाक → ग्रसनी → स्वरयंत्र → श्वासनली → श्वसनी → श्वसनिकाएँ → वायुकोष

4. Nose and Nasal Cavity

नाक से प्रवेश करने वाली हवा:

• Filtered – धूल के कणों को रोका जाता है।
• Warmed – हवा को गर्म किया जाता है।
• Moistened – हवा में नमी मिलाई जाती है।

Nasal cavity में mucus और hair particles को रोकने में सहायता करते हैं।

5. Trachea | श्वासनली

Trachea एक tube-like structure है जो हवा को lungs की ओर ले जाती है। इसकी दीवार में cartilaginous rings होती हैं। इन rings का मुख्य कार्य trachea को collapse होने से बचाने में सहायता करना है।

6. Bronchi और Bronchioles

Trachea दो मुख्य branches में विभाजित होती है जिन्हें bronchi कहते हैं। एक bronchus प्रत्येक lung में प्रवेश करता है। इसके बाद ये छोटी branches में विभाजित होकर bronchioles बनाते हैं।

Bronchioles आगे alveoli तक हवा पहुँचाती हैं।

7. Alveoli – Gas Exchange का मुख्य स्थान

Alveoli छोटे-छोटे balloon-like air sacs होते हैं। इनकी संख्या बहुत अधिक होती है और ये lungs में उपस्थित होते हैं। इनकी विशेषताएँ:

• बहुत बड़ी surface area
• बहुत पतली walls
• अच्छी blood supply
• Gas exchange के लिए उपयुक्त संरचना

8. 🔬 Animated Alveoli – Exchange of Gases

Oxygen and Carbon Dioxide Exchange

🔵 O₂: Alveoli से blood में diffuse करता है।
⚫ CO₂: Blood से alveoli में diffuse करता है और exhalation के दौरान बाहर निकलता है।

9. Exchange of Gases | गैसों का आदान-प्रदान

Alveoli और surrounding blood capillaries के बीच gases का exchange diffusion द्वारा होता है।

Alveoli → O₂ → Blood

Blood → CO₂ → Alveoli

इसके बाद oxygen blood द्वारा body tissues तक पहुँचाई जाती है। Carbon dioxide tissues से blood में आती है और lungs तक पहुँचकर बाहर निकाली जाती है।

10. Alveoli Gas Exchange के लिए उपयुक्त क्यों हैं?

1. Large Surface Area

बहुत अधिक alveoli होने से gas exchange के लिए बड़ी surface area उपलब्ध होती है।

2. Thin Walls

Alveolar walls बहुत पतली होती हैं, जिससे diffusion आसानी से होता है।

3. Rich Blood Supply

Alveoli के चारों ओर blood capillaries का जाल होता है।

4. Moist Surface

Moist surface gases को dissolve होने और diffusion में सहायता करती है।

11. Inhalation | श्वास लेना

जब हम oxygen-rich air अंदर लेते हैं:

• Diaphragm contracts और नीचे की ओर जाता है।
• Rib cage ऊपर और बाहर की ओर move करता है।
• Chest cavity का volume बढ़ता है।
• Lungs expand होते हैं।
• Air lungs में प्रवेश करती है।

Chest Volume ↑ → Pressure ↓ → Air In

12. Exhalation | श्वास छोड़ना

जब हम air बाहर निकालते हैं:

• Diaphragm relax होता है।
• Diaphragm ऊपर की ओर जाता है।
• Chest cavity का volume घटता है।
• Lungs recoil करते हैं।
• Air बाहर निकलती है।

Chest Volume ↓ → Pressure ↑ → Air Out

13. Diaphragm की भूमिका

Diaphragm एक dome-shaped muscular sheet है जो chest cavity और abdominal cavity को अलग करती है। यह breathing में महत्वपूर्ण भूमिका निभाता है।

Inhalation	Exhalation
Diaphragm contracts	Diaphragm relaxes
Moves downward	Moves upward
Chest volume increases	Chest volume decreases
Air enters lungs	Air leaves lungs

14. Oxygen का Transport

Alveoli से oxygen blood में diffuse करता है। Blood में oxygen का अधिकांश भाग haemoglobin से जुड़कर transport होता है।

Haemoglobin + O₂ → Oxyhaemoglobin

यह oxygen को body tissues तक पहुँचाने में सहायता करता है।

15. Carbon Dioxide का Transport

Body cells respiration के दौरान CO₂ बनाती हैं। CO₂ blood द्वारा lungs तक पहुँचाई जाती है। फिर CO₂ blood से alveoli में diffuse होकर exhalation के द्वारा बाहर निकलती है।

16. Tissue Level पर Gas Exchange

Body tissues में oxygen की concentration comparatively कम होती है क्योंकि cells respiration में oxygen का उपयोग करती हैं। इसलिए blood से oxygen tissues में diffuse करती है। CO₂ tissues से blood में diffuse करती है।

Blood O₂ → Body Cells

Body Cells CO₂ → Blood

17. Breathing और Gas Exchange में अंतर

Breathing	Gas Exchange
Air का lungs में आना-जाना।	O₂ और CO₂ का alveoli तथा blood के बीच diffusion।
Inhalation और exhalation शामिल हैं।	Diffusion मुख्य प्रक्रिया है।
Respiratory muscles महत्वपूर्ण हैं।	Thin alveolar walls और capillaries महत्वपूर्ण हैं।

18. Breathing Mechanism – Quick Flow

Inhalation → Chest Volume ↑ → Pressure ↓ → Air Enters

Exhalation → Chest Volume ↓ → Pressure ↑ → Air Leaves

19. Common Respiratory Problems

कुछ सामान्य respiratory disorders:

• Asthma – वायुमार्ग में narrowing/inflammation के कारण breathing difficulty हो सकती है।
• Bronchitis – bronchi की inflammation।
• Pneumonia – lungs के tissues में infection।
• Tuberculosis – एक infectious disease जो lungs को प्रभावित कर सकती है।

20. Complete Process – Air से Cellular Respiration तक

Air ↓ Nose ↓ Trachea ↓ Bronchi ↓ Bronchioles ↓ Alveoli ↓ O₂ enters blood ↓ Haemoglobin transports O₂ ↓ Body Cells ↓ Cellular Respiration ↓ CO₂ ↓ Blood ↓ Lungs ↓ Alveoli ↓ Exhalation

21. MCQs – Multiple Choice Questions

Question 1. The main organ of respiration in humans is:

A) Lungs

B) Kidney

C) Heart

D) Liver

Answer: A

Question 2. Gas exchange in human lungs mainly occurs in:

A) Trachea

B) Alveoli

C) Bronchi

D) Larynx

Answer: B

Question 3. The windpipe is called:

A) Bronchus

B) Pharynx

C) Trachea

D) Alveolus

Answer: C

Question 4. Which muscle plays a major role in breathing?

A) Biceps

B) Diaphragm

C) Triceps

D) Calf muscle

Answer: B

Question 5. Oxygen moves from alveoli to blood mainly by:

A) Osmosis

B) Active transport

C) Diffusion

D) Filtration

Answer: C

Question 6. Oxygen is mainly transported in blood by:

A) Plasma proteins only

B) Haemoglobin

C) Platelets

D) White blood cells

Answer: B

Question 7. During inhalation, diaphragm:

A) Contracts and moves downward

B) Relaxes and moves downward

C) Contracts and moves upward

D) Stops moving

Answer: A

Question 8. During exhalation, chest cavity volume:

A) Increases

B) Decreases

C) Remains same

D) Becomes zero

Answer: B

Question 9. Bronchioles ultimately lead to:

A) Alveoli

B) Kidney

C) Heart

D) Stomach

Answer: A

Question 10. Which gas is removed from the body during exhalation?

A) Nitrogen

B) Oxygen only

C) Carbon dioxide

D) Hydrogen

Answer: C

Question 11. Alveoli have:

A) Thick walls

B) Thin walls

C) No blood supply

D) No moisture

Answer: B

Question 12. Which structure prevents trachea from collapsing?

A) Cartilaginous rings

B) Alveoli

C) Diaphragm

D) Villi

Answer: A

Question 13. Which gas diffuses from blood into alveoli?

A) Oxygen

B) Nitrogen

C) Carbon dioxide

D) Hydrogen

Answer: C

Question 14. Which structure has the largest surface area for gas exchange?

A) Trachea

B) Alveoli

C) Larynx

D) Nose

Answer: B

Question 15. The first part of the respiratory tract is:

A) Nose

B) Bronchi

C) Alveoli

D) Diaphragm

Answer: A

Question 16. Oxyhaemoglobin is formed when:

A) CO₂ combines with haemoglobin

B) O₂ combines with haemoglobin

C) Water combines with haemoglobin

D) Glucose combines with haemoglobin

Answer: B

Question 17. The main purpose of breathing is to:

A) Digest food

B) Exchange respiratory gases

C) Pump blood

D) Produce hormones

Answer: B

Question 18. The walls of alveoli are:

A) One cell thick approximately

B) Very thick

C) Made of bone

D) Made of cartilage

Answer: A

Question 19. During inhalation, air enters lungs because:

A) Lung pressure becomes lower than atmospheric pressure

B) Lung pressure becomes higher

C) Oxygen pulls the lungs

D) Blood pushes air

Answer: A

Question 20. Which organ carries oxygenated blood away from lungs?

A) Pulmonary artery

B) Pulmonary vein

C) Vena cava

D) Aorta only

Answer: B

Question 21. The tiny air sacs of lungs are:

A) Bronchi

B) Alveoli

C) Trachea

D) Larynx

Answer: B

Question 22. Carbon dioxide is produced mainly during:

A) Cellular respiration

B) Digestion only

C) Photosynthesis

D) Transpiration

Answer: A

Question 23. Which structure separates thoracic and abdominal cavities?

A) Bronchus

B) Diaphragm

C) Trachea

D) Alveolus

Answer: B

Question 24. Which condition can make breathing difficult due to narrowing of airways?

A) Asthma

B) Diabetes

C) Anaemia only

D) Rickets

Answer: A

Question 25. The exchange of gases occurs between:

A) Alveoli and blood capillaries

B) Stomach and blood

C) Kidney and lungs

D) Liver and heart

Answer: A

Question 26. Which gas is required by cells for aerobic respiration?

A) CO₂

B) O₂

C) N₂

D) H₂

Answer: B

Question 27. Which structure branches from trachea?

A) Bronchi

B) Alveoli

C) Diaphragm

D) Nose

Answer: A

Question 28. The movement of gases from higher concentration to lower concentration is:

A) Active transport

B) Diffusion

C) Filtration

D) Endocytosis

Answer: B

Question 29. Which blood vessel carries deoxygenated blood from heart to lungs?

A) Pulmonary artery

B) Pulmonary vein

C) Aorta

D) Coronary artery

Answer: A

Question 30. Which feature makes alveoli efficient for gas exchange?

A) Thick walls

B) Small surface area

C) Thin walls and rich blood supply

D) Cartilage rings

Answer: C

22. Subjective Questions – 1 to 6 Marks

1 Mark
Question 1. Name the main respiratory organ in humans.

Answer: Lungs.

1 Mark
Question 2. Where does exchange of gases occur?

Answer: In the alveoli of lungs.

1 Mark
Question 3. Name the windpipe.

Answer: Trachea.

1 Mark
Question 4. Name the pigment that transports most oxygen in blood.

Answer: Haemoglobin.

2 Marks
Question 5. What are alveoli?

Answer: Alveoli are tiny air sacs present in lungs. They provide a large surface area and are the main site of exchange of oxygen and carbon dioxide.

2 Marks
Question 6. What is the function of diaphragm?

Answer: Diaphragm changes the volume of the thoracic cavity during breathing, helping air to enter and leave the lungs.

2 Marks
Question 7. Why are alveoli suitable for gas exchange?

Answer: They have thin walls, large surface area and a rich network of blood capillaries.

3 Marks
Question 8. Explain the pathway of air in the human respiratory system.

Answer: Nostrils → Nasal cavity → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli.

3 Marks
Question 9. Explain gas exchange in alveoli.

Answer: Oxygen diffuses from alveolar air into blood because of the concentration gradient. Carbon dioxide diffuses from blood into alveoli. The CO₂ is then removed during exhalation.

3 Marks
Question 10. What happens during inhalation?

Answer: During inhalation, the diaphragm contracts and moves downward, the chest cavity expands, pressure decreases and air enters the lungs.

4 Marks
Question 11. Explain the mechanism of breathing.

Answer: Breathing involves inhalation and exhalation. During inhalation, diaphragm contracts and moves downward, increasing chest volume and reducing pressure. Air enters lungs. During exhalation, diaphragm relaxes and moves upward, reducing chest volume and increasing pressure, so air moves out.

4 Marks
Question 12. Explain the role of haemoglobin in respiration.

Answer: Haemoglobin present in red blood cells binds with oxygen in the lungs to form oxyhaemoglobin. It transports oxygen to body tissues, where oxygen is released for cellular respiration.

4 Marks
Question 13. Why does gas exchange occur efficiently in alveoli?

Answer: Alveoli have millions of tiny air sacs providing a large surface area. Their walls are very thin and moist. They are surrounded by numerous blood capillaries, allowing rapid diffusion of gases.

5 Marks
Question 14. Describe the structure and function of the human respiratory system.

Answer: The human respiratory system consists of nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and lungs containing alveoli. Air enters through nostrils and travels to alveoli. At alveoli, oxygen enters blood and carbon dioxide leaves blood by diffusion. The respiratory muscles help in inhalation and exhalation.

5 Marks
Question 15. Explain the exchange of oxygen and carbon dioxide between alveoli and blood.

Answer: Oxygen concentration is higher in alveolar air than in deoxygenated blood. Therefore oxygen diffuses into blood. Carbon dioxide concentration is higher in blood than in alveolar air, so CO₂ diffuses into alveoli. CO₂ is subsequently expelled during exhalation.

6 Marks
Question 16. Explain the complete mechanism of respiration in humans.

Answer:

• Air enters through the nostrils.
• It passes through nasal cavity, pharynx, larynx and trachea.
• Trachea divides into bronchi.
• Bronchi divide into bronchioles ending in alveoli.
• Oxygen diffuses from alveoli into blood.
• Haemoglobin transports oxygen to tissues.
• Cells use oxygen during aerobic respiration and produce CO₂.
• CO₂ is transported back to lungs and diffuses into alveoli.
• CO₂ is removed during exhalation.

6 Marks
Question 17. Explain inhalation and exhalation with the role of diaphragm.

Answer: Inhalation: Diaphragm contracts and becomes flatter. Chest volume increases and pressure decreases. Air enters the lungs.

Exhalation: Diaphragm relaxes and becomes dome-shaped. Chest volume decreases and pressure increases. Air moves out of the lungs.

23. CBSE Exam Golden Points ⭐

• Alveoli are the main site of gas exchange.
• Gas exchange occurs by diffusion.
• O₂ moves from alveoli to blood.
• CO₂ moves from blood to alveoli.
• Haemoglobin transports most oxygen in blood.
• Diaphragm plays a major role in breathing.
• Inhalation → diaphragm contracts and moves downward.
• Exhalation → diaphragm relaxes and moves upward.
• Alveoli have thin walls and rich blood supply.
• Large alveolar surface area makes gas exchange efficient.

24. One-Minute Revision

Nose → Trachea → Bronchi → Bronchioles → Alveoli

Alveoli → O₂ → Blood → Body Cells

Body Cells → CO₂ → Blood → Alveoli → Outside

Inhalation: Volume ↑ → Pressure ↓ → Air In

Exhalation: Volume ↓ → Pressure ↑ → Air Out

Class 10th Science Chapter 5 – Life Processes | Respiration – Aerobic and Anaerobic Respiration

Life Processes – Respiration

Class 10 Science | Aerobic and Anaerobic Respiration | CBSE + Foundation + Competitive

Respiration – Aerobic and Anaerobic Respiration

1. Respiration क्या है? | What is Respiration?

English:
Respiration is the biochemical process by which food molecules such as glucose are broken down to release energy.

हिन्दी:
श्वसन (Respiration) वह जैव-रासायनिक प्रक्रिया है जिसमें ग्लूकोज जैसे भोजन के अणुओं का विघटन करके ऊर्जा मुक्त की जाती है।

यह ऊर्जा मुख्य रूप से ATP (Adenosine Triphosphate) के रूप में उपलब्ध होती है।

2. Respiration की आवश्यकता | Need of Respiration

जीवों को विभिन्न जीवन-क्रियाओं के लिए ऊर्जा की आवश्यकता होती है।

• Growth – वृद्धि
• Movement – गति
• Repair – कोशिकीय मरम्मत
• Active transport – सक्रिय परिवहन
• Cell division – कोशिका विभाजन
• Body temperature and other metabolic activities

मुख्य विचार:

Food + Oxygen → Energy + Carbon Dioxide + Water

यह समीकरण विशेष रूप से aerobic respiration को दर्शाता है।

3. Breathing और Respiration में अंतर

Breathing	Respiration
Breathing is the physical process of taking in oxygen and giving out carbon dioxide.	Respiration is a biochemical process that releases energy from food.
यह मुख्यतः गैसों का आदान-प्रदान है।	यह कोशिकाओं के अंदर होने वाली रासायनिक प्रक्रिया है।
Breathing occurs through respiratory organs.	Respiration occurs inside cells.
Breathing does not directly release usable cellular energy.	Respiration releases energy in usable form such as ATP.

4. Glucose का विघटन | Breakdown of Glucose

Respiration की शुरुआत कोशिका के cytoplasm में glucose के टूटने से होती है। Glucose का molecular formula:

C₆H₁₂O₆

Glucose सबसे पहले टूटकर Pyruvate बनाता है।

Glucose (C₆H₁₂O₆) → Pyruvate

यह प्रारम्भिक चरण glycolysis कहलाता है।

5. Glycolysis | ग्लाइकोलाइसिस

English:
Glycolysis is the first stage of glucose breakdown. It occurs in the cytoplasm of the cell.

हिन्दी:
ग्लाइकोलाइसिस ग्लूकोज के विघटन का पहला चरण है। यह कोशिका के cytoplasm में होता है।

इस प्रक्रिया में एक glucose molecule से दो pyruvate molecules बनते हैं।

C₆H₁₂O₆ → 2 Pyruvate

इसके बाद pyruvate की आगे की प्रक्रिया oxygen की उपलब्धता पर निर्भर करती है।

6. Pyruvate के तीन प्रमुख मार्ग

Condition	Pathway	Products
Presence of oxygen	Aerobic respiration	CO₂ + H₂O + large amount of energy
Absence of oxygen in yeast	Alcoholic fermentation	Ethanol + CO₂ + some energy
Insufficient oxygen in muscle cells	Lactic acid fermentation	Lactic acid + some energy

7. Aerobic Respiration | वायवीय श्वसन

Definition:
Aerobic respiration is the breakdown of glucose in the presence of oxygen to release energy.

हिन्दी:
वायवीय श्वसन वह प्रक्रिया है जिसमें oxygen की उपस्थिति में glucose का पूर्ण विघटन होता है और अधिक मात्रा में ऊर्जा मुक्त होती है।

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

Aerobic respiration में glucose का लगभग पूर्ण oxidation होता है। इसके मुख्य products:

• Carbon dioxide – CO₂
• Water – H₂O
• Energy – ATP

यह प्रक्रिया मुख्य रूप से mitochondria में आगे जारी रहती है। इसलिए mitochondria को अक्सर: Powerhouse of the cell कहा जाता है।

8. Anaerobic Respiration | अवायवीय श्वसन

Definition:
Anaerobic respiration is the breakdown of glucose in the absence of oxygen.

हिन्दी:
अवायवीय श्वसन वह प्रक्रिया है जिसमें oxygen की अनुपस्थिति में glucose का अपूर्ण विघटन होता है।

Glucose → Ethanol + CO₂ + Energy

यह प्रक्रिया yeast में alcoholic fermentation के रूप में देखी जाती है।

9. Yeast में Anaerobic Respiration

Yeast एक unicellular microorganism है। Oxygen की कमी में yeast glucose को ethanol और carbon dioxide में बदलता है।

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy

यह प्रक्रिया: Alcoholic fermentation कहलाती है।

Uses:

• Bread making
• Alcohol production
• Fermentation industries

Bread बनाने में CO₂ dough को फूलाने में सहायता करता है।

10. Muscle Cells में Anaerobic Respiration

जब हम बहुत तेज physical exercise करते हैं, तब muscles को oxygen की आवश्यकता तेजी से बढ़ जाती है। कभी-कभी oxygen की supply demand से कम पड़ जाती है। ऐसी स्थिति में muscle cells में pyruvate का परिवर्तन lactic acid में हो सकता है।

Glucose → Lactic Acid + Energy

या सरल रूप में:

Pyruvate → Lactic Acid + Energy

Important: Muscles में lactic acid का accumulation थकान और cramps से associated हो सकता है। Exercise के बाद oxygen supply सामान्य होने पर lactic acid आगे metabolise किया जा सकता है।

11. Mitochondria की भूमिका

Mitochondria कोशिका का प्रमुख energy-releasing organelle है। Aerobic respiration में glucose breakdown से प्राप्त pyruvate mitochondria में आगे process होता है। इस प्रक्रिया से अधिक मात्रा में ATP बनती है।

Mitochondria = Major site of aerobic energy release

12. ATP क्या है? | What is ATP?

ATP का पूरा नाम: Adenosine Triphosphate ATP को कोशिका की energy currency कहा जाता है। जब ATP टूटता है तो usable energy उपलब्ध होती है।

ATP → ADP + Pi + Energy

यह energy cellular activities में उपयोग की जाती है।

13. Aerobic और Anaerobic Respiration में अंतर

Basis	Aerobic Respiration	Anaerobic Respiration
Oxygen	Oxygen required	Oxygen not required
Glucose breakdown	More complete	Incomplete
Products	CO₂ + H₂O	Ethanol + CO₂ or Lactic acid
Energy	More energy	Less energy
Main site	Cytoplasm + mitochondria	Mainly cytoplasm
Examples	Most plants and animals under normal oxygen supply	Yeast and muscle cells under oxygen shortage

14. Energy Release की तुलना

Aerobic respiration में glucose का अधिक complete breakdown होने के कारण anaerobic respiration की तुलना में अधिक energy release होती है।

Aerobic Respiration → More Energy

Anaerobic Respiration → Less Energy

15. Plants में Respiration

Plants भी respiration करते हैं। Plants में respiration के लिए oxygen का उपयोग और carbon dioxide का release होता है। Plants में गैसों का exchange मुख्यतः:

• Stomata – leaves
• Lenticels – stems
• Root surface – roots

के माध्यम से होता है।

16. Photosynthesis और Respiration का संबंध

Photosynthesis	Respiration
Food is synthesised.	Food is broken down.
Usually requires light.	Occurs continuously in living cells.
CO₂ is used.	CO₂ is released in aerobic respiration.
O₂ is released.	O₂ is used in aerobic respiration.
Energy is stored in food.	Energy is released from food.

17. Respiration का महत्व

Respiration द्वारा प्राप्त energy का उपयोग:

1. Growth
2. Movement
3. Repair
4. Cell division
5. Active transport
6. Synthesis of cellular materials
7. Maintenance of life processes

18. Quick Concept Summary

Concept	Key Point
Respiration	Food breakdown to release energy.
Glycolysis	Glucose → 2 Pyruvate; occurs in cytoplasm.
Aerobic	Uses oxygen and releases more energy.
Anaerobic	Does not require oxygen and releases less energy.
Yeast	Produces ethanol + CO₂.
Muscles	Can produce lactic acid when oxygen is insufficient.
ATP	Usable energy currency of the cell.
Mitochondria	Main site of aerobic energy release.

19. MCQs – Multiple Choice Questions

Question 1. Respiration is mainly concerned with:

A) Release of energy from food

B) Formation of chlorophyll

C) Absorption of sunlight

D) Formation of soil

Answer: A

Question 2. Glycolysis occurs in:

A) Nucleus

B) Cytoplasm

C) Ribosome

D) Chloroplast

Answer: B

Question 3. The first major product of glucose breakdown is:

A) Ethanol

B) Lactic acid

C) Pyruvate

D) Oxygen

Answer: C

Question 4. Aerobic respiration requires:

A) Nitrogen

B) Carbon dioxide

C) Hydrogen

D) Oxygen

Answer: D

Question 5. The main products of aerobic respiration are:

A) Ethanol and CO₂

B) CO₂ and H₂O

C) Lactic acid and oxygen

D) Glucose and oxygen

Answer: B

Question 6. Anaerobic respiration in yeast produces:

A) Ethanol and CO₂

B) Water and oxygen

C) Glucose and oxygen

D) Only water

Answer: A

Question 7. During vigorous exercise, muscle cells may produce:

A) Ethanol

B) Methane

C) Lactic acid

D) Acetic acid

Answer: C

Question 8. ATP stands for:

A) Adenine Transfer Protein

B) Adenosine Triphosphate

C) Active Transport Protein

D) Adenosine Tetraphosphate

Answer: B

Question 9. Mitochondria are mainly associated with:

A) Aerobic respiration

B) Photosynthesis

C) Protein synthesis only

D) Digestion

Answer: A

Question 10. Anaerobic respiration releases:

A) More energy than aerobic respiration

B) Equal energy

C) Less energy

D) No energy

Answer: C

Question 11. Fermentation in yeast is associated with formation of:

A) Lactic acid

B) Ethanol

C) Oxygen

D) Glucose

Answer: B

Question 12. Carbon dioxide is released during:

A) Aerobic respiration

B) Photosynthesis only

C) Water absorption

D) Mineral uptake

Answer: A

Question 13. Which molecule is called the energy currency of the cell?

A) DNA

B) RNA

C) ATP

D) Glucose

Answer: C

Question 14. Complete aerobic respiration produces:

A) Ethanol

B) Lactic acid

C) Methane

D) Carbon dioxide and water

Answer: D

Question 15. Which organism commonly performs alcoholic fermentation?

A) Yeast

B) Human RBC

C) Earthworm

D) Fish

Answer: A

Question 16. Glucose contains:

A) 6 carbon atoms

B) 5 carbon atoms

C) 4 carbon atoms

D) 3 carbon atoms

Answer: A

Question 17. The formula of glucose is:

A) C₂H₅OH

B) CH₄

C) C₆H₁₂O₆

D) CO₂

Answer: C

Question 18. When oxygen is insufficient in muscles, pyruvate may form:

A) Ethanol

B) Lactic acid

C) Methanol

D) Glucose

Answer: B

Question 19. The physical process of taking oxygen into the body is:

A) Respiration

B) Digestion

C) Breathing

D) Excretion

Answer: C

Question 20. Which process releases more energy from one glucose molecule?

A) Aerobic respiration

B) Anaerobic respiration

C) Fermentation only

D) None

Answer: A

Question 21. During alcoholic fermentation, pyruvate is converted into:

A) Protein

B) Ethanol and CO₂

C) Oxygen

D) Water only

Answer: B

Question 22. Respiration is:

A) An energy-releasing process

B) A process of sunlight absorption

C) A process of water filtration

D) A process of DNA copying only

Answer: A

Question 23. The organelle known as the powerhouse of the cell is:

A) Nucleus

B) Golgi body

C) Mitochondria

D) Ribosome

Answer: C

Question 24. Which is NOT a product of aerobic respiration?

A) Carbon dioxide

B) Water

C) Energy

D) Ethanol

Answer: D

Question 25. Bread dough rises mainly due to:

A) Oxygen

B) Carbon dioxide

C) Nitrogen

D) Hydrogen

Answer: B

Question 26. Anaerobic respiration occurs:

A) Only in plants

B) Only in animals

C) In the absence of oxygen

D) Only in chloroplasts

Answer: C

Question 27. Which process is associated with lactic acid formation?

A) Photosynthesis

B) Anaerobic respiration in muscles

C) Digestion

D) Transpiration

Answer: B

Question 28. Which gas is generally consumed during aerobic respiration?

A) Oxygen

B) Carbon dioxide

C) Nitrogen

D) Hydrogen

Answer: A

Question 29. The first stage of glucose breakdown occurs in:

A) Nucleus

B) Cytoplasm

C) Vacuole

D) Cell wall

Answer: B

Question 30. Which statement is correct?

A) Anaerobic respiration always produces more energy.

B) Aerobic respiration does not use oxygen.

C) Yeast can perform alcoholic fermentation.

D) Respiration occurs only during daytime.

Answer: C

20. Subjective Questions – 1 to 6 Marks

1 Mark
Question 1. What is respiration?

Answer: Respiration is the process of breakdown of food to release energy.

1 Mark
Question 2. Where does glycolysis occur?

Answer: Glycolysis occurs in the cytoplasm.

1 Mark
Question 3. Name the energy currency of the cell.

Answer: ATP – Adenosine Triphosphate.

1 Mark
Question 4. Name the product formed during anaerobic respiration in yeast.

Answer: Ethanol and carbon dioxide are formed.

2 Marks
Question 5. Differentiate between breathing and respiration.

Answer: Breathing is the physical exchange of gases, whereas respiration is the biochemical breakdown of food to release energy.

2 Marks
Question 6. What is aerobic respiration?

Answer: Aerobic respiration is the breakdown of glucose in the presence of oxygen, producing carbon dioxide, water and energy.

2 Marks
Question 7. What is anaerobic respiration?

Answer: Anaerobic respiration is the breakdown of glucose without oxygen. It produces less energy and products such as ethanol and CO₂ in yeast or lactic acid in muscles.

2 Marks
Question 8. Why is ATP called the energy currency of the cell?

Answer: ATP stores usable chemical energy and releases it when required for cellular activities. Therefore, it is called the energy currency of the cell.

3 Marks
Question 9. Explain glycolysis.

Answer: Glycolysis is the first stage of glucose breakdown. It occurs in the cytoplasm. One glucose molecule is converted into two pyruvate molecules with release of some energy.

3 Marks
Question 10. Explain anaerobic respiration in yeast.

Answer: In the absence of oxygen, yeast breaks down glucose to form ethanol, carbon dioxide and a small amount of energy.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy

3 Marks
Question 11. Why do muscles develop cramps during vigorous exercise?

Answer: During vigorous exercise, oxygen supply may become insufficient for the increased energy demand. Muscle cells may then carry out anaerobic respiration, producing lactic acid. Accumulation of lactic acid is associated with muscle fatigue and cramps.

3 Marks
Question 12. Write the equation for aerobic respiration.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

4 Marks
Question 13. Differentiate between aerobic and anaerobic respiration.

Answer:

• Aerobic respiration requires oxygen; anaerobic respiration does not.
• Aerobic respiration involves more complete breakdown of glucose.
• Aerobic respiration releases more energy.
• Anaerobic respiration produces ethanol + CO₂ in yeast or lactic acid in muscles.

4 Marks
Question 14. Explain the fate of pyruvate under different conditions.

Answer:

• In the presence of oxygen → CO₂ + H₂O + more energy.
• In yeast without oxygen → ethanol + CO₂ + some energy.
• In muscle cells with insufficient oxygen → lactic acid + some energy.

4 Marks
Question 15. Explain the role of mitochondria in respiration.

Answer: Mitochondria are the major site of aerobic energy release. Pyruvate formed during glycolysis enters mitochondria and is further oxidised in the presence of oxygen. This results in the formation of CO₂, water and a large amount of usable energy.

4 Marks
Question 16. Explain why aerobic respiration releases more energy than anaerobic respiration.

Answer: In aerobic respiration glucose undergoes a more complete oxidation in the presence of oxygen. Therefore, more chemical energy stored in glucose becomes available as ATP. Anaerobic respiration involves incomplete breakdown, so less energy is released.

5 Marks
Question 17. Describe the complete process of glucose breakdown during respiration.

Answer:

• Glucose first undergoes glycolysis in the cytoplasm.
• One glucose molecule forms two pyruvate molecules.
• In the presence of oxygen, pyruvate is further oxidised in mitochondria.
• Carbon dioxide and water are formed.
• A large amount of energy is released and stored in ATP.

5 Marks
Question 18. Explain aerobic and anaerobic respiration with suitable equations.

Answer: Aerobic respiration occurs in the presence of oxygen:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

Anaerobic respiration occurs without oxygen. In yeast:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy

In muscles under oxygen shortage:

Pyruvate → Lactic Acid + Energy

5 Marks
Question 19. Explain fermentation and mention its applications.

Answer: Fermentation is an anaerobic process in which microorganisms such as yeast convert sugars into products such as ethanol and carbon dioxide. Applications include:

• Alcohol production
• Bread making
• Food processing
• Industrial production of fermented products

6 Marks
Question 20. Explain respiration in detail and compare aerobic and anaerobic respiration.

Answer: Respiration is the biochemical breakdown of food to release energy. Glucose first undergoes glycolysis in the cytoplasm and forms pyruvate. Aerobic pathway:

Glucose + O₂ → CO₂ + H₂O + Large amount of Energy

Anaerobic pathway in yeast:

Glucose → Ethanol + CO₂ + Small amount of Energy

In muscle cells under oxygen shortage:

Pyruvate → Lactic Acid + Energy

Aerobic respiration produces more energy because glucose is more completely oxidised.

6 Marks
Question 21. Draw/describe the pathway of glucose breakdown.

Glucose
↓
Glycolysis
↓
2 Pyruvate

From pyruvate:

With Oxygen
↓
CO₂ + H₂O + More Energy

Without Oxygen – Yeast
↓
Ethanol + CO₂ + Less Energy

Insufficient Oxygen – Muscles
↓
Lactic Acid + Less Energy

6 Marks
Question 22. Why is respiration essential for survival?

Answer: Respiration provides energy required for all essential life processes. The released energy is used for growth, movement, repair, active transport, synthesis of biomolecules, cell division and maintenance of cellular functions. Without continuous energy supply, cells cannot perform their vital activities.

3 Marks
Question 23. Why does yeast produce alcohol in the absence of oxygen?

Answer: In the absence of oxygen, yeast cannot carry out aerobic respiration efficiently. It therefore obtains energy through anaerobic fermentation, during which glucose is converted into ethanol and carbon dioxide.

3 Marks
Question 24. Why is anaerobic respiration less efficient?

Answer: Anaerobic respiration involves incomplete breakdown of glucose. A significant amount of chemical energy remains in the products such as ethanol or lactic acid. Hence, less energy is released.

2 Marks
Question 25. Name the two types of respiration based on oxygen requirement.

Answer: 1. Aerobic respiration
2. Anaerobic respiration

2 Marks
Question 26. Name the two products of alcoholic fermentation.

Answer: Ethanol and carbon dioxide.

3 Marks
Question 27. What happens to pyruvate when oxygen is available?

Answer: When oxygen is available, pyruvate enters mitochondria and undergoes further oxidation, producing carbon dioxide, water and a large amount of energy.

4 Marks
Question 28. Why are mitochondria called the powerhouse of the cell?

Answer: Mitochondria are the major site of aerobic respiration and produce a large amount of ATP. Since ATP supplies usable energy for cellular activities, mitochondria are commonly called the powerhouse of the cell.

5 Marks
Question 29. Explain the importance of ATP in living organisms.

Answer: ATP stores chemical energy in a readily usable form. Energy released during respiration is captured in ATP. When the cell requires energy, ATP can be broken down to release it. This energy is used for movement, active transport, synthesis, growth, repair and other cellular activities.

6 Marks
Question 30. Explain the complete difference between aerobic and anaerobic respiration with examples and equations.

Feature	Aerobic	Anaerobic
Oxygen	Required	Not required
Breakdown	More complete	Incomplete
Energy	More	Less
Products	CO₂ + H₂O	Ethanol + CO₂ or lactic acid
Example	Normal cellular respiration	Yeast / oxygen-starved muscles

Aerobic equation:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

Yeast anaerobic equation:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy

21. HOTS / Competency Based Questions

HOTS 1. A person runs very fast for a short period and experiences muscle fatigue. Why?

Answer: Vigorous exercise may temporarily reduce oxygen availability to muscles. Anaerobic respiration can then occur, producing lactic acid and contributing to muscle fatigue.

HOTS 2. Why does bread become soft and porous when yeast is added?

Answer: Yeast performs fermentation and releases CO₂. The gas gets trapped in the dough and causes it to expand, making bread porous.

HOTS 3. Why is aerobic respiration considered more efficient?

Answer: It involves more complete oxidation of glucose and therefore releases more usable energy.

HOTS 4. Why cannot cells depend only on anaerobic respiration for normal energy requirements?

Answer: Anaerobic respiration releases much less energy per glucose molecule and produces partially oxidised products.

22. CBSE Exam Golden Points

⭐ Remember:

• Respiration releases energy from food.
• Glycolysis occurs in cytoplasm.
• Glucose forms pyruvate during glycolysis.
• Aerobic respiration requires oxygen.
• Anaerobic respiration does not require oxygen.
• Aerobic respiration releases more energy.
• Yeast produces ethanol + CO₂ during fermentation.
• Muscle cells can produce lactic acid during oxygen shortage.
• Mitochondria are the major site of aerobic energy release.
• ATP is the energy currency of the cell.

23. One-Line Revision

Glucose → Glycolysis → Pyruvate → Different pathways depending on oxygen availability.

O₂ present: CO₂ + H₂O + More Energy
O₂ absent in yeast: Ethanol + CO₂ + Less Energy
O₂ insufficient in muscles: Lactic Acid + Less Energy

Class 10th Science Chapter 5 – Life Processes | Human Digestive System and Digestion

Life Processes – Human Digestive System and Digestion

Class 10 Science | Chapter 6 | CBSE + Foundation + Competitive Level

🧑‍🔬 Human Digestive System and Digestion

1. पाचन क्या है? | What is Digestion?

English:
Digestion is the process of breaking down complex, insoluble food substances into simpler, soluble substances that can be absorbed and utilized by the body.

हिन्दी:
पाचन वह प्रक्रिया है जिसमें जटिल और अघुलनशील भोजन पदार्थों को सरल और घुलनशील पदार्थों में परिवर्तित किया जाता है, ताकि शरीर उन्हें अवशोषित करके उपयोग कर सके।

Key Idea:
Large food molecules → Smaller soluble molecules → Absorption → Utilization

मुख्य विचार:
बड़े भोजन अणु → छोटे घुलनशील अणु → अवशोषण → उपयोग

2. पाचन की आवश्यकता | Why is Digestion Necessary?

Food contains complex substances such as carbohydrates, proteins and fats. Most of these cannot be directly absorbed in their complex form. Therefore, digestion converts them into simpler substances.

Complex Food	Digested Form
Carbohydrates / Starch	Simple sugars such as glucose
Proteins	Amino acids
Fats	Fatty acids + Glycerol

3. मानव पाचन तंत्र | Human Digestive System

The human digestive system consists of the alimentary canal and associated digestive glands.

मानव पाचन तंत्र में आहार नाल (Alimentary Canal) तथा उससे संबंधित पाचन ग्रंथियाँ शामिल होती हैं।

Mouth → Buccal Cavity → Pharynx → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus

मुख → मुखगुहा → ग्रसनी → ग्रासनली → आमाशय → छोटी आंत → बड़ी आंत → मलाशय → गुदा

Mouth

→

Oesophagus

→

Stomach

→

Small Intestine

→

Large Intestine

→

Rectum

→

Anus

4. मुखगुहा | Mouth / Buccal Cavity

Digestion begins in the mouth. The mouth contains teeth, tongue and salivary glands.

Teeth: Cut, tear and grind food.
Tongue: Mixes food with saliva, helps in swallowing and helps in taste.
Salivary glands: Produce saliva containing the enzyme salivary amylase.

Starch → Maltose / Simpler Sugars
Salivary Amylase

Exam Point:
Salivary amylase begins the digestion of starch in the mouth.

परीक्षा बिंदु:
लार में उपस्थित सैलिवरी एमाइलेज मुख में स्टार्च के पाचन की शुरुआत करता है।

5. दाँत और उनके कार्य | Teeth and Their Functions

Type of Teeth	Function
Incisors	Cutting and biting
Canines	Tearing food
Premolars	Crushing and grinding
Molars	Grinding and crushing

6. ग्रासनली | Oesophagus

The oesophagus is a muscular tube connecting the pharynx to the stomach. Food is pushed towards the stomach by rhythmic muscular contractions called peristalsis.

ग्रासनली एक पेशीय नली है जो ग्रसनी को आमाशय से जोड़ती है। भोजन लयबद्ध पेशीय संकुचन क्रमाकुंचन (Peristalsis) द्वारा आमाशय की ओर जाता है।

7. आमाशय | Stomach

The stomach is a muscular, J-shaped organ. It stores food temporarily and mixes it with gastric juice. Gastric juice contains hydrochloric acid, pepsin and mucus.

आमाशय एक पेशीय, J-आकार का अंग है। यह भोजन को कुछ समय के लिए संग्रहित करता है तथा उसे जठर रस के साथ मिलाता है। जठर रस में हाइड्रोक्लोरिक अम्ल, पेप्सिन और म्यूकस प्रमुख घटक हैं।

Component	Function
Hydrochloric Acid (HCl)	Provides acidic medium and helps activate pepsin; also helps kill many microbes.
Pepsin	Begins digestion of proteins into smaller peptides.
Mucus	Protects the stomach lining from acid and digestive enzymes.

Important:
HCl does not directly digest proteins. It creates the acidic medium required for pepsin activity.

8. छोटी आंत | Small Intestine

The small intestine is the main site of complete digestion and absorption of digested nutrients. It receives digestive juices from the pancreas and intestinal glands, and bile from the liver.

छोटी आंत पाचन की पूर्णता और पचे हुए पोषक पदार्थों के अवशोषण का मुख्य स्थान है। इसमें अग्न्याशय और आंतों से पाचक रस तथा यकृत से पित्त पहुँचता है।

9. पित्त रस | Bile

Bile is produced by the liver and stored in the gall bladder. It helps in the digestion of fats mainly by emulsifying fats into tiny droplets, increasing the surface area for lipase action. Bile also helps provide an alkaline medium for intestinal digestion.

पित्त रस का निर्माण यकृत में होता है और यह पित्ताशय में संग्रहित रहता है। यह वसा को छोटी-छोटी बूंदों में विभाजित करके वसीय पायसीकरण (Emulsification) करता है, जिससे लाइपेज की क्रिया अधिक प्रभावी होती है।

Remember:
Liver → Produces bile
Gall bladder → Stores and concentrates bile
Bile → Helps in fat digestion by emulsification

10. अग्न्याशय | Pancreas

The pancreas secretes pancreatic juice containing enzymes that help digest carbohydrates, proteins and fats.

अग्न्याशय पैंक्रियाटिक रस का स्राव करता है जिसमें कार्बोहाइड्रेट, प्रोटीन और वसा के पाचन में सहायता करने वाले एंजाइम होते हैं।

Pancreatic Enzyme	Main Action
Pancreatic amylase	Acts on starch/carbohydrates
Trypsin	Acts on proteins/peptides
Lipase	Acts on fats

11. आंतों का रस | Intestinal Juice

Intestinal glands secrete intestinal juice containing enzymes that complete the digestion of carbohydrates, proteins and other food components.

आंतों की ग्रंथियाँ आंतों के रस का स्राव करती हैं। इसके एंजाइम कार्बोहाइड्रेट और प्रोटीन आदि के पाचन को पूर्ण करने में सहायता करते हैं।

12. कार्बोहाइड्रेट का पाचन | Digestion of Carbohydrates

Location	Major Event
Mouth	Salivary amylase begins starch digestion.
Stomach	Little carbohydrate digestion because acidic conditions inhibit salivary amylase.
Small Intestine	Pancreatic and intestinal enzymes complete digestion into simple sugars.

Starch → Maltose / Smaller Sugars → Glucose

13. प्रोटीन का पाचन | Digestion of Proteins

Location	Major Event
Stomach	Pepsin begins protein digestion.
Small Intestine	Pancreatic and intestinal proteases continue and complete digestion.

Proteins → Peptides → Amino Acids

14. वसा का पाचन | Digestion of Fats

Bile emulsifies fats into smaller droplets. Lipase then breaks fats into fatty acids and glycerol.

पित्त वसा को छोटी बूंदों में विभाजित करता है। इसके बाद लाइपेज वसा को वसीय अम्ल और ग्लिसरॉल में तोड़ता है।

Fats → Emulsification → Fatty Acids + Glycerol

15. आंतों की विल्ली | Villi

The inner lining of the small intestine contains numerous finger-like projections called villi. Villi greatly increase the surface area available for absorption of digested food. Each villus contains blood capillaries and a lymph vessel called a lacteal.

छोटी आंत की आंतरिक सतह पर अंगुलीनुमा उंगली जैसी संरचनाएँ विल्ली (Villi) होती हैं। ये अवशोषण के लिए सतह क्षेत्र को बहुत बढ़ाती हैं। प्रत्येक विल्ली में रक्त केशिकाएँ और लैक्टियल नामक लसीका वाहिका होती है।

Exam Point:
Villi increase the surface area for efficient absorption of digested nutrients.

16. बड़ी आंत | Large Intestine

The large intestine mainly absorbs water and some salts from the remaining material. The remaining waste is stored in the rectum and is eventually expelled through the anus.

बड़ी आंत मुख्यतः शेष पदार्थ से जल और कुछ लवणों का अवशोषण करती है। बचा हुआ अपशिष्ट मलाशय में संग्रहित होता है और अंततः गुदा द्वारा बाहर निकाला जाता है।

17. पाचन ग्रंथियाँ | Digestive Glands

Gland / Organ	Secretion	Main Role
Salivary glands	Saliva	Begins starch digestion
Gastric glands	Gastric juice	Protein digestion and acidic medium
Liver	Bile	Fat emulsification
Pancreas	Pancreatic juice	Digestion of carbohydrates, proteins and fats
Intestinal glands	Intestinal juice	Completes digestion

18. भोजन की पूरी यात्रा | Complete Journey of Food

Ingestion

→

Mouth

→

Oesophagus

→

Stomach

→

Small Intestine

→

Absorption

→

Large Intestine

→

Egestion

19. अवशोषण और आत्मसातीकरण | Absorption and Assimilation

Absorption: Passage of digested nutrients from the alimentary canal into blood or lymph.

Assimilation: Utilization of absorbed nutrients by body cells for energy, growth, repair and other functions.

अवशोषण: पचे हुए पोषक पदार्थों का आहार नाल से रक्त या लसीका में जाना।
आत्मसातीकरण: कोशिकाओं द्वारा अवशोषित पोषक पदार्थों का उपयोग करना।

20. मलत्याग | Egestion

Egestion is the removal of undigested food from the alimentary canal through the anus. It is different from excretion.

मलत्याग वह प्रक्रिया है जिसमें अपचित भोजन को गुदा द्वारा शरीर से बाहर निकाला जाता है। यह उत्सर्जन (Excretion) से अलग प्रक्रिया है।

Egestion	Excretion
Removal of undigested food	Removal of metabolic wastes
Through anus	Through organs such as kidneys, lungs and skin

21. Human Digestion – Complete Summary

Organ	Main Function
Mouth	Ingestion, chewing and beginning of starch digestion
Oesophagus	Movement of food by peristalsis
Stomach	Storage, mixing and beginning of protein digestion
Liver	Produces bile
Gall bladder	Stores bile
Pancreas	Produces pancreatic digestive enzymes
Small intestine	Complete digestion and major absorption
Large intestine	Absorbs water and salts
Rectum	Stores faeces
Anus	Expels faeces

22. MCQs – Multiple Choice Questions

Q1. Digestion is the process of:

A) Breaking complex food into simpler substances

B) Producing oxygen

C) Removing urine

D) Pumping blood

Answer: A) Breaking complex food into simpler substances

Q2. Digestion of starch begins in the:

A) Stomach

B) Mouth

C) Large intestine

D) Rectum

Answer: B) Mouth

Q3. Which enzyme is present in saliva?

A) Pepsin

B) Lipase

C) Salivary amylase

D) Trypsin

Answer: C) Salivary amylase

Q4. Movement of food through the oesophagus occurs by:

A) Diffusion

B) Osmosis

C) Filtration

D) Peristalsis

Answer: D) Peristalsis

Q5. Which acid is present in gastric juice?

A) Hydrochloric acid

B) Sulphuric acid

C) Nitric acid

D) Carbonic acid

Answer: A) Hydrochloric acid

Q6. Which enzyme begins protein digestion in the stomach?

A) Amylase

B) Pepsin

C) Lipase

D) Maltase

Answer: B) Pepsin

Q7. The organ that produces bile is:

A) Pancreas

B) Stomach

C) Liver

D) Small intestine

Answer: C) Liver

Q8. Bile is stored in the:

A) Pancreas

B) Stomach

C) Small intestine

D) Gall bladder

Answer: D) Gall bladder

Q9. The main function of bile in digestion is:

A) Emulsification of fats

B) Digestion of proteins

C) Digestion of starch in the mouth

D) Absorption of glucose

Answer: A) Emulsification of fats

Q10. Which organ secretes pancreatic juice?

A) Liver

B) Pancreas

C) Stomach

D) Gall bladder

Answer: B) Pancreas

Q11. Complete digestion mainly occurs in the:

A) Mouth

B) Oesophagus

C) Small intestine

D) Large intestine

Answer: C) Small intestine

Q12. The finger-like projections in the small intestine are called:

A) Nephrons

B) Alveoli

C) Bronchi

D) Villi

Answer: D) Villi

Q13. The main function of villi is:

A) Increase surface area for absorption

B) Produce bile

C) Store food

D) Produce saliva

Answer: A) Increase surface area for absorption

Q14. Proteins are finally digested into:

A) Fatty acids

B) Amino acids

C) Glucose

D) Glycerol

Answer: B) Amino acids

Q15. Fats are mainly broken down into:

A) Glucose and amino acids

B) Starch and glucose

C) Fatty acids and glycerol

D) Peptides and amino acids

Answer: C) Fatty acids and glycerol

Q16. Which part mainly absorbs water from undigested material?

A) Mouth

B) Stomach

C) Small intestine

D) Large intestine

Answer: D) Large intestine

Q17. The temporary storage of faeces occurs in the:

A) Rectum

B) Stomach

C) Small intestine

D) Oesophagus

Answer: A) Rectum

Q18. Which structure prevents the stomach wall from being damaged by gastric juice?

A) Bile

B) Mucus

C) Saliva

D) Villi

Answer: B) Mucus

Q19. Which substance provides an acidic medium in the stomach?

A) Bile

B) Saliva

C) HCl

D) Pancreatic juice

Answer: C) HCl

Q20. Which organ receives bile and pancreatic juice?

A) Stomach

B) Oesophagus

C) Large intestine

D) Small intestine

Answer: D) Small intestine

Q21. The process of taking food into the body is:

A) Ingestion

B) Absorption

C) Assimilation

D) Egestion

Answer: A) Ingestion

Q22. Passage of digested nutrients into blood or lymph is called:

A) Digestion

B) Absorption

C) Ingestion

D) Egestion

Answer: B) Absorption

Q23. Utilization of absorbed nutrients by cells is called:

A) Digestion

B) Ingestion

C) Assimilation

D) Egestion

Answer: C) Assimilation

Q24. Removal of undigested food is called:

A) Absorption

B) Assimilation

C) Excretion

D) Egestion

Answer: D) Egestion

Q25. Which digestive gland produces saliva?

A) Salivary glands

B) Liver

C) Pancreas

D) Gastric glands

Answer: A) Salivary glands

Q26. Which teeth are mainly used for tearing food?

A) Incisors

B) Canines

C) Molars

D) Premolars

Answer: B) Canines

Q27. Which enzyme digests fats?

A) Pepsin

B) Amylase

C) Lipase

D) Trypsin

Answer: C) Lipase

Q28. Which enzyme helps digest proteins in the small intestine?

A) Amylase

B) Lipase

C) Maltase

D) Trypsin

Answer: D) Trypsin

Q29. Which organ is both a digestive gland and an important metabolic organ?

A) Liver

B) Oesophagus

C) Rectum

D) Teeth

Answer: A) Liver

Q30. Which sequence is correct?

A) Stomach → Mouth → Small intestine → Oesophagus

B) Mouth → Oesophagus → Stomach → Small intestine

C) Mouth → Stomach → Oesophagus → Large intestine

D) Oesophagus → Mouth → Stomach → Small intestine

Answer: B) Mouth → Oesophagus → Stomach → Small intestine

23. Subjective Questions – 1 to 6 Marks

1 Mark
Q1. Define digestion.

Digestion is the breakdown of complex food into simpler, soluble substances that can be absorbed and utilized.

1 Mark
Q2. Name the enzyme present in saliva.

Salivary amylase.

1 Mark
Q3. What is peristalsis?

Peristalsis is the rhythmic muscular movement that pushes food through the alimentary canal.

2 Marks
Q4. What are the functions of saliva?

1. It moistens and lubricates food.
2. Salivary amylase begins the digestion of starch.

2 Marks
Q5. What is the role of HCl in the stomach?

HCl provides an acidic medium required for pepsin activity and also helps kill many microorganisms entering with food.

2 Marks
Q6. What is the function of bile?

Bile helps emulsify fats into small droplets and contributes to an alkaline medium for digestion in the small intestine.

3 Marks
Q7. State three functions of the stomach.

1. Stores food temporarily.
2. Mixes food with gastric juice.
3. Begins protein digestion through pepsin.

3 Marks
Q8. Why is the small intestine important in digestion?

The small intestine is the main site where digestion is completed. It receives bile, pancreatic juice and intestinal secretions. It also contains villi for efficient absorption of digested nutrients.

3 Marks
Q9. What are villi? State their importance.

Villi are finger-like projections lining the small intestine. They greatly increase the surface area for absorption and contain blood capillaries and lymph vessels to transport absorbed nutrients.

4 Marks
Q10. Explain digestion of carbohydrates in humans.

Carbohydrate digestion begins in the mouth where salivary amylase acts on starch. In the stomach, carbohydrate digestion is greatly reduced because the acidic medium inhibits salivary amylase. In the small intestine, pancreatic and intestinal enzymes continue and complete carbohydrate digestion into simple sugars such as glucose.

4 Marks
Q11. Explain digestion of proteins in humans.

Protein digestion begins in the stomach. HCl provides the acidic medium for pepsin, which begins breaking proteins into smaller peptides. In the small intestine, pancreatic and intestinal proteases continue digestion and convert peptides into simpler substances, ultimately amino acids.

4 Marks
Q12. Explain digestion of fats.

Bile produced by the liver emulsifies fats into small droplets. This increases their surface area. Lipase then acts on the fats and breaks them into fatty acids and glycerol.

5 Marks
Q13. Describe the human alimentary canal.

The human alimentary canal is a continuous muscular tube consisting mainly of:

1. Mouth: Ingestion and beginning of starch digestion.
2. Oesophagus: Transports food by peristalsis.
3. Stomach: Stores food and begins protein digestion.
4. Small intestine: Completes digestion and absorbs nutrients.
5. Large intestine: Absorbs water and salts.
6. Rectum: Stores faeces.
7. Anus: Expels faeces.

5 Marks
Q14. Explain the role of different digestive glands.

Salivary glands: Produce saliva containing salivary amylase.

Gastric glands: Produce HCl, pepsin and mucus.

Liver: Produces bile.

Pancreas: Produces pancreatic juice containing digestive enzymes.

Intestinal glands: Produce intestinal secretions that help complete digestion.

6 Marks
Q15. Explain the complete process of digestion in humans from mouth to anus.

1. Mouth: Food is chewed and mixed with saliva. Salivary amylase begins starch digestion.

2. Oesophagus: Food moves towards the stomach through peristalsis.

3. Stomach: Food is mixed with gastric juice. HCl creates an acidic medium and pepsin begins protein digestion. Mucus protects the stomach lining.

4. Small intestine: Bile emulsifies fats. Pancreatic and intestinal enzymes complete digestion of carbohydrates, proteins and fats.

5. Absorption: Villi absorb digested nutrients into blood and lymph.

6. Large intestine and anus: Water is absorbed, faeces are stored in the rectum and finally expelled through the anus.

6 Marks
Q16. Draw/describe the pathway of food through the human digestive system and mention the main function of each part.

Mouth → Pharynx → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus

Part	Main Function
Mouth	Chewing and initial starch digestion
Oesophagus	Peristaltic movement
Stomach	Storage and protein digestion
Small Intestine	Complete digestion and absorption
Large Intestine	Water and salt absorption
Rectum	Temporary storage of faeces
Anus	Egestion

24. HOTS – Higher Order Thinking Questions

Q17. Why does digestion not occur in the oesophagus?

The main function of the oesophagus is to transport food from the pharynx to the stomach by peristalsis. It does not contain major digestive glands responsible for significant digestion.

Q18. Why is bile important even though it does not contain a digestive enzyme?

Bile emulsifies fats into tiny droplets, increasing the surface area available for lipase action. It also helps provide a suitable alkaline medium for intestinal digestion.

Q19. Why are villi numerous and finger-like?

Their large number and finger-like shape greatly increase the surface area available for absorption of digested nutrients.

Q20. Why is mucus important in the stomach?

Mucus forms a protective layer over the stomach lining and helps protect it from hydrochloric acid and digestive enzymes.

25. Quick Revision – परीक्षा के लिए महत्वपूर्ण बिंदु

🧠 Mouth → Chewing + Saliva + Starch digestion

🧠 Oesophagus → Peristalsis

🧠 Stomach → HCl + Pepsin + Mucus + Protein digestion

🧠 Liver → Produces bile

🧠 Gall bladder → Stores bile

🧠 Pancreas → Pancreatic digestive enzymes

🧠 Small intestine → Complete digestion + major absorption

🧠 Villi → Increase absorption surface area

🧠 Large intestine → Water and salt absorption

🧠 Rectum → Stores faeces

🧠 Anus → Egestion

26. Master Revision Table

Food Component	Major End Product of Digestion
Carbohydrates	Simple sugars such as glucose
Proteins	Amino acids
Fats	Fatty acids + Glycerol

27. CBSE Exam Golden Points

• Digestion converts complex food into simpler absorbable substances.
• Digestion of starch begins in the mouth.
• Salivary amylase is present in saliva.
• Peristalsis moves food through the alimentary canal.
• Pepsin begins protein digestion in the stomach.
• HCl provides the acidic medium in the stomach.
• Mucus protects the stomach lining.
• Liver produces bile.
• Gall bladder stores bile.
• Bile emulsifies fats.
• Pancreas secretes pancreatic juice.
• Small intestine is the main site of complete digestion and absorption.
• Villi increase the surface area for absorption.
• Large intestine mainly absorbs water and some salts.
• Egestion is different from excretion.

28. One-Line Master Revision

Mouth → Starch Digestion → Oesophagus → Peristalsis → Stomach → Protein Digestion → Small Intestine → Complete Digestion + Absorption → Large Intestine → Water Absorption → Rectum → Storage → Anus → Egestion