This MCQ module is based on: Respiration in Organisms – Cellular and Human
TOPIC 18 OF 50
Respiration in Organisms – Cellular and Human
🎓 Class 10
Science
CBSE
Theory
Ch 5 — Life Processes
⏱ ~17 min
🌐 Language: [gtranslate]
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5.3 Respiration — Releasing Energy from Food
Digestion ends with nutrients like glucose entering our cells. But glucose by itself cannot be "used" directly. The energy locked up inside it must first be released and repackaged into a molecule the cell can actually spend — ATP (adenosine triphosphate). This controlled release of energy from food molecules inside cells is cellular respiration, and it happens in every single living cell.
Aerobic vs Anaerobic Respiration
| Feature | Aerobic respiration | Anaerobic respiration |
|---|---|---|
| Oxygen required? | Yes | No |
| End products | CO₂ + H₂O + energy | Ethanol + CO₂ (yeast) or Lactic acid (muscles) |
| Energy yield | ~38 ATP per glucose (large) | ~2 ATP per glucose (small) |
| Site in cell | Cytoplasm (start) + Mitochondria (complete) | Cytoplasm only |
| Examples | Most plants and animals | Yeast (fermentation); working muscle cells |
Aerobic: Glucose + 6 O₂ → 6 CO₂ + 6 H₂O + Energy (≈38 ATP)
Yeast (anaerobic): Glucose → 2 Ethanol + 2 CO₂ + Energy (≈2 ATP)
Muscle (anaerobic): Glucose → 2 Lactic acid + Energy (≈2 ATP)
Why do your legs cramp after a sprint? During vigorous exercise, your heart and lungs cannot supply oxygen fast enough to the leg muscles. The muscle cells switch partially to anaerobic respiration, producing lactic acid. Lactic acid build-up irritates the muscle fibres and produces that painful cramp. Rest and deep breathing let oxygen reach the muscles again and clear the lactic acid.
5.3.1 Respiration in Plants
Plants also respire — all the time, in every living cell, day and night. The confusion students sometimes have is because plants also photosynthesise during daylight, which releases a lot of oxygen and hides their own respiration. At night, only respiration continues and a net release of CO₂ is seen.
Gas exchange in plants has three channels:
- Leaves exchange gases through stomata.
- Stems (woody ones) have pore-like lenticels on the bark.
- Roots take up O₂ dissolved in the soil through their root hairs.
Because plants don't have large muscles and don't move around, their energy demand is low, and slow diffusion is enough to supply each cell with O₂.
5.3.2 Respiration in Human Beings
Humans need a lot of oxygen very fast. We solve this with a specialised respiratory system plus a pumping chest. Air enters the nostrils, where hair and mucus filter out dust; passes through the pharynx and larynx (voice box); goes down the trachea (windpipe, kept open by C-shaped cartilage rings); splits into two bronchi (one into each lung); branches again and again into finer bronchioles; and finally ends in millions of tiny balloon-like sacs called alveoli.
Mechanism of Breathing
Breathing is a mechanical process carried out by two sets of muscles: the dome-shaped diaphragm that separates the chest from the belly, and the intercostal muscles between the ribs.
| Step | Diaphragm | Ribs | Chest volume | Air |
|---|---|---|---|---|
| Inspiration (breathe in) | Contracts, flattens (moves down) | Move up and outward | Increases | Rushes in (pressure drops) |
| Expiration (breathe out) | Relaxes, domes up | Move down and inward | Decreases | Pushed out |
Gas Exchange at the Alveoli
Each alveolus is wrapped in a fine net of blood capillaries. The alveolar wall is only one cell thick, and so is the capillary wall. Across this ultra-thin barrier, oxygen diffuses from alveolar air into the blood (because O₂ is higher in the alveoli than in returning deoxygenated blood), and carbon dioxide diffuses the other way (because CO₂ is higher in the blood). The oxygen is then carried almost entirely by the red pigment haemoglobin inside red blood cells. This oxygenated blood returns to the heart and is pumped out to every tissue in the body.
Activity 5.2 — Lime Water Test for Exhaled AirL3 Apply
Predict first: If you blow into a tube dipped in clear lime water, will the lime water stay clear? Why do you say so?
- Take a test tube with freshly prepared clear lime water (Ca(OH)₂).
- Dip a clean drinking straw into the lime water and gently exhale through the straw for about a minute.
- Observe what happens to the lime water.
The lime water turns milky. This confirms that exhaled air contains carbon dioxide, which reacts with calcium hydroxide to form insoluble calcium carbonate:
Ca(OH)₂ + CO₂ → CaCO₃ ↓ + H₂O
Since CO₂ is a waste product of cellular respiration, this activity proves we breathe out CO₂.
Respiration in Other Animals
| Animal group | Breathing organ | How it works |
|---|---|---|
| Fish | Gills | Extract dissolved O₂ from water flowing over gill filaments |
| Insects | Trachea + spiracles | A network of air tubes opens to the outside through holes (spiracles) and delivers O₂ directly to every tissue |
| Frogs (amphibians) | Skin (when wet) + lungs | Moist skin allows gas exchange underwater; lungs are used on land |
| Earthworms | Skin | Gases diffuse through the moist body surface |
Interactive — Respiration Type Predictor
Pick a situation and see which mode of respiration is mostly in use.
Click a button above…
Competency-Based Questions
Rahul runs a 200-metre race. After finishing, he pants heavily and feels his leg muscles ache. A few minutes later, the cramps subside.
1. During the sprint, what substance builds up in Rahul's leg muscles? L2
(b) Lactic acid. Oxygen supply cannot keep up with demand, so muscles briefly switch to anaerobic respiration.
2. Fill-in-the-blank: Aerobic respiration yields about ____ ATP per glucose while anaerobic yields only ____ ATP. L1
38 and 2.
3. Why does Rahul pant heavily after the race? L3
Rapid breathing brings in extra oxygen. This oxygen is used to oxidise the lactic acid accumulated in his muscles, repaying the so-called "oxygen debt".
4. True or False: Alveoli are designed for gas exchange by having thick walls. L1
False. Alveolar walls are very thin (one cell thick) to allow fast diffusion of gases.
5. Long answer: List three design features of alveoli that maximise gas exchange. L4
(i) Millions of alveoli provide an enormous total surface area (~80 m²). (ii) Walls are only one cell thick so diffusion distance is minimal. (iii) Each alveolus is surrounded by a dense network of capillaries maintaining steep concentration gradients of O₂ and CO₂.
Assertion–Reason Questions
(A) Both true, R explains A · (B) Both true, R does not explain A · (C) A true, R false · (D) A false, R true
A: Plants release more O₂ than CO₂ during the day.
R: During the day, rate of photosynthesis exceeds the rate of respiration.
(A) — Photosynthesis produces O₂ faster than respiration consumes it during daylight.
A: Trachea does not collapse when air pressure falls inside it.
R: C-shaped rings of cartilage keep the trachea permanently open.
(A) — Correct reasoning.
A: Aerobic respiration yields more energy than anaerobic respiration.
R: In anaerobic respiration, glucose is only partially broken down.
(A) — Incomplete breakdown leaves most chemical energy still locked inside ethanol or lactic acid.
Frequently Asked Questions — Cellular & Human Respiration
What is cellular & human respiration in Class 10 Science (CBSE board)?
Cellular & Human Respiration is a key topic in NCERT Class 10 Science Chapter 5 — Life Processes. It explains aerobic and anaerobic respiration, glycolysis, atp and the mechanism of human breathing. Core ideas covered include respiration, aerobic respiration, anaerobic respiration, glycolysis. Mastering this subtopic is essential for scoring well in the CBSE Class 10 Science board exam because board papers repeatedly test these concepts through MCQs, short answers and long-answer questions. This part gives a complete, exam-ready explanation with activities, diagrams and competency-based practice aligned to NCERT.
Why is respiration important in NCERT Class 10 Science?
Respiration is important in NCERT Class 10 Science because it forms the foundation for understanding cellular & human respiration in Chapter 5 — Life Processes. Without a clear idea of respiration, students cannot answer higher-order CBSE board questions involving aerobic respiration, anaerobic respiration, glycolysis. Board papers regularly include 2-mark and 3-mark questions on this concept, and competency-based questions often link respiration to real-life situations. Building clarity here pays off directly in board marks.
How is cellular & human respiration tested in the Class 10 Science CBSE board exam?
The CBSE Class 10 Science board exam tests cellular & human respiration through a mix of 1-mark MCQs, 2-mark short answers, 3-mark explanations with examples, 5-mark descriptive questions (often with diagrams or balanced equations) and 4-mark competency-based questions. Expect direct questions on respiration, aerobic respiration, anaerobic respiration and application-based questions drawn from NCERT activities. Students who follow NCERT thoroughly and practice this chapter's questions consistently score in the 90%+ range.
What are the key terms to remember for cellular & human respiration in Class 10 Science?
The key terms to remember for cellular & human respiration in NCERT Class 10 Science Chapter 5 are: respiration, aerobic respiration, anaerobic respiration, glycolysis, mitochondria, ATP. Each of these concepts carries exam weightage and regularly appears in the CBSE board paper. Write clear one-line definitions of every term in your revision notes and revisit them before the exam. Linking these terms visually through a flowchart or concept map makes recall easier during the Class 10 Science board exam.
Is Cellular & Human Respiration included in the Class 10 Science syllabus for 2025–26 CBSE board exam?
Yes, Cellular & Human Respiration is a part of the NCERT Class 10 Science syllabus (2025–26) prescribed by CBSE. It falls under Chapter 5 — Life Processes — and is examined in the annual board paper. The current syllabus retains the full treatment of respiration, aerobic respiration, anaerobic respiration as per the NCERT textbook. Because CBSE bases every board question on NCERT, studying this part thoroughly ensures complete syllabus coverage and guarantees marks from this chapter.
How should I prepare cellular & human respiration for the CBSE Class 10 Science board exam?
Prepare cellular & human respiration for the CBSE Class 10 Science board exam in three steps. First, read this NCERT part carefully, highlighting definitions and diagrams of respiration, aerobic respiration, anaerobic respiration. Second, solve every in-text question and end-of-chapter exercise — CBSE questions often come directly from NCERT. Third, practice competency-based and assertion-reason questions to sharpen reasoning. Write answers in the exam-style format (point-wise with diagrams) and time yourself. This method delivers confidence and full marks in the board exam.
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