Chapter 3 of 11

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Andhra Pradesh (BIEAP)Class 10 Biological Science★ AP Board (BSEAP) SSC Biological Science · ~6 marks · Board: AP Board

Respiration — Aerobic and Anaerobic

RESPIRATION — the process that releases ENERGY from food. AEROBIC (with oxygen, 38 ATP, in mitochondria) vs ANAEROBIC (without oxygen, 2 ATP, in cytoplasm). The HUMAN RESPIRATORY SYSTEM — every organ explained. ATP as the energy currency. Fermentation and muscle cramps. AP Board Class 10 Biological Science.

⏱ 16 min readMedium difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Distinguish breathing (gas exchange) from cellular respiration (energy release)
2Write the equation for aerobic respiration; compare with anaerobic respiration
3Describe the human respiratory system: organs and their functions
4Explain the mechanism of inhalation and exhalation — role of diaphragm and intercostal muscles
5Explain gas exchange in alveoli — structure and adaptations

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Why this chapter matters

Respiration explains how cells release energy from food — the fundamental energy process of all life. Aerobic and anaerobic respiration, the equation for cellular respiration, and the human respiratory system are all tested in AP SSC. The distinction between breathing (exchange of gases) and respiration (cellular energy release) is commonly misunderstood and tested. The mechanism of breathing (diaphragm and rib muscles) and gas exchange in alveoli are standard 4-mark explanation questions.

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AP Board Class 9 Science: breathing and exchange of gases basics

Respiration — Class 10 Biological Science

"You breathe 20,000 times a day. Every breath is your body's way of getting OXYGEN to release ENERGY from the food you ate. Respiration is life."

1. About the Chapter

Respiration is the biochemical process that RELEASES ENERGY from GLUCOSE. This chapter covers:

Aerobic respiration: Complete breakdown of glucose using oxygen → 38 ATP
Anaerobic respiration: Partial breakdown without oxygen → 2 ATP (fermentation, lactic acid)
The human respiratory system: Every organ, the mechanism of breathing, gas exchange at the alveoli
ATP: The energy currency of the cell

Why This Matters

Respiration happens in EVERY living cell, EVERY second
Understanding aerobic vs anaerobic explains MUSCLE CRAMPS during exercise
Fermentation is the basis of bread, idli, dosa, and alcohol production
Respiratory diseases (asthma, bronchitis) are among India's most common health problems

2. Respiration ≠ Breathing

Breathing (Ventilation)	Respiration (Cellular)
PHYSICAL — inhaling and exhaling air	CHEMICAL — breaking glucose to release energy
Occurs in the LUNGS	Occurs in EVERY CELL
Involves MUSCLES (diaphragm, intercostals)	Involves ENZYMES
NO ATP produced	ATP PRODUCED

'You breathe to BRING OXYGEN to your cells — and to REMOVE the carbon dioxide respiration produces. Breathing SERVES respiration.'

3. Aerobic Respiration (With Oxygen)

The Equation

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP

Three Stages

Stage	Location	What Happens	ATP
1. Glycolysis	CYTOPLASM	Glucose (6C) → 2 Pyruvate (3C). Does NOT need O₂.	2
2. Krebs Cycle	MITOCHONDRIAL MATRIX	Pyruvate → Acetyl CoA → cycle. Carbon released as CO₂. NADH, FADH₂ produced.	2
3. Electron Transport Chain	INNER MITOCHONDRIAL MEMBRANE	NADH and FADH₂ pass electrons through protein chain. OXYGEN is FINAL acceptor → forms WATER. H⁺ flow through ATP synthase.	~34

Total per glucose: ~38 ATP

The Role of Oxygen

'Oxygen is the FINAL ELECTRON ACCEPTOR in the ETC. Without oxygen: the ETC STOPS. Krebs Cycle stops. Only glycolysis continues — producing just 2 ATP. This is why you DIE without oxygen — cells cannot produce enough energy to survive.'

4. Anaerobic Respiration (Without Oxygen)

Only GLYCOLYSIS occurs. Pyruvate is converted to OTHER products. Only 2 ATP produced.

Type 1 — Alcoholic Fermentation (Yeast)

Glucose → 2 Ethanol + 2 CO₂ + 2 ATP Uses: Bread (CO₂ makes dough RISE). Beer and wine. Idli/dosa batter fermentation. 'The spongy texture of idli comes from CO₂ produced by yeast fermentation!'

Type 2 — Lactic Acid Fermentation (Muscles)

Glucose → 2 Lactic Acid + 2 ATP During INTENSE exercise: oxygen supply cannot meet demand. Muscle cells switch to ANAEROBIC. Lactic acid ACCUMULATES → burning sensation and CRAMPS. 'After rest: deep breathing supplies oxygen. Lactic acid is OXIDISED. Cramps fade.'

Aerobic vs Anaerobic

Feature	Aerobic	Anaerobic
Oxygen	Required	NOT required
Location	Mitochondria	Cytoplasm ONLY
Glucose breakdown	COMPLETE → CO₂ + H₂O	INCOMPLETE → ethanol or lactic acid
ATP per glucose	~38	2
Occurs in	Most organisms	Yeast (fermentation). Muscles (heavy exercise).

5. The Human Respiratory System

The Path of Air

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

Organ	Function
Nasal Cavity	Filters dust (mucus + cilia). WARMS and MOISTENS air.
Larynx	VOICE BOX. Vocal cords vibrate → sound.
Trachea	C-shaped CARTILAGE RINGS — keeps airway open.
Alveoli	TINY air sacs (~300 million per lung). ONE cell thick. Surrounded by capillaries. 'Total surface area ~70 m² — size of a tennis court!'

Breathing Mechanism

Inhalation: Diaphragm CONTRACTS (flattens). Rib cage EXPANDS. Lung volume ↑. Pressure ↓. Air rushes IN. Exhalation: Diaphragm RELAXES (dome). Rib cage contracts. Lung volume ↓. Pressure ↑. Air pushed OUT.

Gas Exchange at Alveoli

O₂ (high in alveolar air) → diffuses → INTO blood → binds to HAEMOGLOBIN (oxyhaemoglobin). CO₂ (high in blood) → diffuses → OUT of blood → into alveolar air → EXHALED. 'Gas exchange is by DIFFUSION — molecules move from HIGH to LOW concentration.'

6. ATP — The Energy Currency

ATP = Adenosine Triphosphate. Three phosphate groups with HIGH-ENERGY BONDS. When energy needed: ATP → ADP + Pi + ENERGY (7.3 kcal/mol). 'ATP is a RECHARGEABLE BATTERY. Spent ADP is recharged using energy from respiration.'

7. Respiration in Plants

Plants RESPIRE ALL THE TIME — day and night. During DAY: photosynthesis produces O₂ — used by the plant for respiration. Excess O₂ released. At NIGHT: only respiration. Plant TAKES IN O₂, gives out CO₂. 'Never sleep under a tree at night — it competes with you for oxygen.' Gas exchange through: STOMATA (leaves). LENTICELS (stems — small pores). Root hairs (diffusion from soil air).

8. Common Mistakes

'Respiration = breathing' — Breathing is VENTILATION. Respiration is CELLULAR — breaking glucose for energy. Breathing SUPPLIES oxygen for respiration.
'Plants only respire at night' — Plants respire ALL THE TIME. During the day, photosynthesis produces MORE O₂ than respiration consumes — masking it.
'38 ATP from cytoplasm' — Only GLYCOLYSIS (2 ATP) occurs in cytoplasm. Remaining 36 ATP from MITOCHONDRIA.
'Yeast produces lactic acid' — YEAST → ethanol + CO₂. MUSCLES → lactic acid. 'Know which organism produces which!'
'Oxygen is used in glycolysis' — Glycolysis does NOT require oxygen. The Krebs Cycle and ETC REQUIRE oxygen.

9. AP SSC Exam Focus

Topic	Marks	Type
Aerobic vs Anaerobic	3-4	Short Answer / Table
Respiratory system diagram	4-5	Diagram labelling
Mechanism of breathing	3-4	Short Answer
Fermentation (yeast & muscles)	2-3	MCQ
ATP and energy	2-3	MCQ

Key Diagram: Draw and label the HUMAN RESPIRATORY SYSTEM.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Respiration Equations

AEROBIC RESPIRATION: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP). Occurs in MITOCHONDRIA. Complete oxidation. ANAEROBIC RESPIRATION (in yeast): C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + Energy (ATP). (Fermentation). ANAEROBIC (in muscle): C₆H₁₂O₆ → 2C₃H₆O₃ (lactic acid) + Energy. (Causes muscle fatigue — 'oxygen debt'). RESPIRATORY ORGANS: Nose (filter, warm, moisten) → Pharynx → Larynx (voice box) → Trachea → Bronchi → Bronchioles → Alveoli (gas exchange). BREATHING MECHANISM: INHALATION: Diaphragm contracts (moves DOWN). External intercostal muscles contract (ribs move UP and OUT). Lung volume INCREASES. Pressure DECREASES. Air rushes IN. EXHALATION: Diaphragm RELAXES (moves UP). Internal intercostal muscles contract (ribs move IN and DOWN). Lung volume DECREASES. Pressure INCREASES. Air pushed OUT.

AP SSC IMPORTANT DISTINCTION: BREATHING = physical process of taking in air and releasing it. RESPIRATION = chemical process of breaking down glucose using O₂ to release ATP energy. All cells respire. Breathing involves lungs. ALVEOLI ADAPTATIONS: Thin walls (one cell thick). Large surface area (300 million alveoli per lung). Rich blood supply (capillaries). Moist surface (CO₂ and O₂ dissolve and diffuse). These features maximise gas exchange efficiency.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Confusing breathing and respiration

✓ BREATHING: The MECHANICAL process of moving air in and out of the lungs. Involves diaphragm and rib muscles. Happens in the RESPIRATORY SYSTEM. RESPIRATION: The CHEMICAL process where cells break down glucose using oxygen to release ENERGY (ATP). Happens in ALL CELLS (in the MITOCHONDRIA). A student's muscles respire even while they are not actively breathing — respiration is continuous in all living cells. Respiration releases energy; breathing supplies oxygen for respiration.

Practice problems

Work through this chapter's problems as a readiness check — reveal each solution, mark yourself honestly, and get your gap report at the end.

Readiness check

Are you exam-ready for Respiration — Aerobic and Anaerobic?

1 problems from this chapter. Try each one, reveal the worked solution, mark yourself honestly — get your gap report at the end.

1 questions~2 min

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP. Occurs in mitochondria.
•Anaerobic respiration in yeast: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP (fermentation).
•Anaerobic respiration in muscles: glucose → lactic acid + 2 ATP. Lactic acid causes muscle cramps.
•Aerobic produces 38 ATP; anaerobic produces only 2 ATP — aerobic is 19× more efficient.
•Breathing = mechanical process (air in/out of lungs). Cellular respiration = chemical process (glucose → ATP in cells). These are NOT the same.
•Inhalation: diaphragm contracts (flattens down), ribs move up and out, lung volume increases, pressure drops, air enters.
•Exhalation: diaphragm relaxes (domes up), ribs drop, lung volume decreases, pressure rises, air exits.
•Alveoli — 5 adaptations: 300 million per lung (large area ~70 m²), walls one cell thick (short diffusion path), moist lining (gases dissolve), rich capillary network, elastic (recoil during exhalation).
•Oxygen debt: muscle lactic acid must be converted back to glucose in the liver after exercise — this needs O₂, hence heavy breathing continues after exercise stops.
•Yeast fermentation is used in bread making (CO₂ makes dough rise) and alcohol production.

Andhra Pradesh (BIEAP) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Fermentation in food and beverage industry

Beer, wine, bread, idli, dosa batter, and yoghurt all depend on microbial fermentation — a direct industrial application of anaerobic respiration. The bread industry alone uses millions of tonnes of yeast annually. Understanding the glucose → ethanol + CO₂ pathway is the science behind it all.

Altitude sickness and acclimatisation

At high altitudes, oxygen partial pressure drops. The body compensates by increasing breathing rate, producing more red blood cells, and increasing haemoglobin concentration — all responses to maintain cellular respiration in low-oxygen conditions. Understanding the oxygen delivery chain is critical for mountaineering physiology and medicine.

CPR and emergency medicine

Cardiopulmonary resuscitation (CPR) works on the principle that cells can survive brief periods without oxygen if blood flow can be maintained. Brain cells begin dying within 4–6 minutes without O₂ because they have no anaerobic backup — they depend entirely on aerobic respiration. This is why CPR must begin immediately and why brain death precedes cardiac death in oxygen deprivation.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Write BOTH anaerobic equations separately — yeast (ethanol + CO₂) and muscle (lactic acid). Combining them or writing only one loses half the marks.

The breathing mechanism question (4 marks) requires a step-by-step description: name the muscle (diaphragm/intercostal), state what it does (contracts/relaxes), state the effect on volume, state the effect on pressure, state the direction of air flow. Missing any step costs marks.

Alveoli adaptations — always write 5 points with brief explanations. Listing without explaining does not earn full marks.

Distinguish breathing from respiration at the start of any question that involves either term — examiners reward this distinction explicitly.

ATP number: aerobic = 38 ATP, anaerobic = 2 ATP. State this in any question comparing aerobic vs anaerobic to show you understand the efficiency difference.

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

STRETCH

Research the three stages of aerobic respiration: Glycolysis (cytoplasm), Krebs cycle (mitochondrial matrix), and Electron Transport Chain (inner mitochondrial membrane). Understand why 38 ATP are produced in total.

STRETCH

The anaerobic pathway in yeast produces ethanol — but in humans, the product is lactate, not ethanol. This is because humans lack the enzyme alcohol dehydrogenase in muscles. Research what would happen if human muscles produced ethanol instead.

STRETCH

Explore the role of NAD⁺ and FAD as electron carriers in cellular respiration — understanding these coenzymes explains why both aerobic and anaerobic pathways can occur from the same initial glycolysis step.

STRETCH

Research the cyanide-resistant pathway in some plant mitochondria — plants have an alternative oxidase that allows respiration to continue even when cyanide blocks the standard electron transport chain.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

AP Board SSC (Class 10)High — breathing mechanism and aerobic/anaerobic equations are standard 4+2 mark questions

NEET (UG Medical Entrance)Very High — respiration is a Class 11 chapter tested in detail in NEET; all three stages (glycolysis, Krebs, ETC) are examined

AP EAMCET (Bioscience)High — cellular respiration and breathing mechanisms are standard Class 11 biology topics

Junior Science Olympiad (NSO/SSTSE)Moderate — application questions on ATP production and fermentation appear in science olympiad papers

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Questions students ask

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Aerobic respiration requires oxygen — and during intense exercise, the blood cannot deliver oxygen fast enough to meet the muscles' ATP demand. Anaerobic respiration requires no oxygen and produces ATP instantly, though wastefully. It is the emergency fuel system. The cost is lactic acid buildup, which causes the burning sensation and cramps. After exercise, the body repays the 'oxygen debt' by breathing heavily to oxidise the lactic acid.

Yeast carries out anaerobic fermentation of sugar: glucose → ethanol + CO₂. The CO₂ gas gets trapped in the dough, forming bubbles that cause the dough to rise and become light. When the bread is baked, the heat kills the yeast, the ethanol evaporates, and the expanded air pockets are set permanently by the cooked starch. This is a direct real-world application of anaerobic respiration.

Muscles working harder consume more oxygen and produce more CO₂. Elevated CO₂ lowers blood pH, which is detected by chemoreceptors in the medulla oblongata and carotid bodies. These send signals to increase breathing rate and depth — to exhale more CO₂ and inhale more O₂. It is the CO₂ rise (not just low O₂) that primarily triggers faster breathing.

Both release the same total energy (about 2,870 kJ/mol of glucose) and produce CO₂ and water. But combustion releases all the energy at once as heat and light. Cellular respiration releases energy in controlled small steps across 30+ enzyme-catalysed reactions, capturing ~40% as ATP (usable energy) and releasing the rest as heat (~37°C body temperature). Enzymes, step-wise reactions, and ATP production are the critical differences.

Yes — ALL living cells (including plant cells) carry out cellular respiration continuously, day and night. Photosynthesis occurs only in the light and only in chloroplasts. Respiration occurs in the dark too, in all cells, in mitochondria. During the day, a plant's photosynthesis produces far more O₂ than its respiration consumes, so it appears to only release O₂. At night, only respiration occurs, so it takes in O₂ and releases CO₂.

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