This MCQ module is based on: Respiration in Animals
TOPIC 33 OF 46
Respiration in Animals
🎓 Class 7
Science
CBSE
Theory
Ch 9 — Life Processes in Animals
⏱ ~14 min
🌐 Language: [gtranslate]
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[myaischool_lt_science_assessment grade_level="class_7" science_domain="biology" difficulty="basic"]
9.8 Why Do We Breathe?
Hold your breath. How long can you manage? Ten seconds? Twenty? A minute? Sooner or later, your body will force you to gasp for air. Every cell in your body — from your toenail to your brain — needs a steady supply of oxygen to keep the energy-making machinery running. The same cells also produce a waste gas, carbon dioxide, which must be thrown out. This two-way gas exchange is the job of the respiratory system.
Think first: When you run very fast, you pant. When you rest, your breathing is slow and steady. Why does the body change its breathing rate like this?
9.9 Breathing vs Cellular Respiration
These two ideas sound similar but happen in different places.
- Breathing is a physical action — the movement of air into and out of the lungs. One breath = one inhalation + one exhalation.
- Cellular respiration is a chemical change — the cells of the body use oxygen to break down glucose (a sugar from food) and release the energy stored in it. The waste products are carbon dioxide and water.
Word equation of cellular respiration (with oxygen):
\[ \text{Glucose} + \text{Oxygen} \longrightarrow \text{Carbon dioxide} + \text{Water} + \text{Energy} \] Breathing supplies the oxygen needed for this reaction and carries the carbon dioxide away.
\[ \text{Glucose} + \text{Oxygen} \longrightarrow \text{Carbon dioxide} + \text{Water} + \text{Energy} \] Breathing supplies the oxygen needed for this reaction and carries the carbon dioxide away.
9.10 Aerobic and Anaerobic Respiration
Usually our cells use oxygen — this is called aerobic respiration. But sometimes — during a fast sprint, or in a muscle that is working overtime — oxygen cannot reach the cells quickly enough. The cells then switch briefly to a backup method called anaerobic respiration, which releases much less energy and leaves behind lactic acid. Lactic acid build-up is what makes your legs ache after a race.
Aerobic respiration (with oxygen)
Glucose + Oxygen → Carbon dioxide + Water + lots of energy
Happens in the cells of humans, cows, fish, insects and most animals — all the time.
Anaerobic respiration (without oxygen)
Glucose → Lactic acid + small energy (in muscles during heavy exercise)
In yeast: Glucose → Alcohol + CO₂ + energy (this is used to make bread and curd rise).
9.11 Breathing in Humans
Air enters through the nostrils, travels down the windpipe (trachea), and reaches two spongy organs called lungs. Inside the lungs, the air goes into millions of tiny air sacs called alveoli, where oxygen slips into the blood and carbon dioxide comes out.
How the Diaphragm Pumps Air
- Inhalation: The diaphragm flattens downwards and the rib muscles lift the ribs up and out. The chest cavity becomes larger, and air rushes in to fill the extra space.
- Exhalation: The diaphragm arches up again and the ribs move back. The chest cavity shrinks, and air is pushed out of the lungs.
A resting adult breathes about 12–18 times per minute. A young child breathes a little faster, and a sleeping baby slower. During running, the rate can double to meet the extra demand for oxygen. The amount of air your lungs can hold after the deepest possible breath is called the lung capacity — about 5 litres in an adult male.
Why You Cannot Hold Your Breath Forever
When you hold your breath, oxygen in the blood begins to drop and carbon dioxide begins to rise. A tiny area in the brain senses this and forces you to breathe again. Most people cannot hold their breath for more than 30–60 seconds without training. Free-divers who train for years can manage a few minutes — but never forever, because the brain always wins in the end.
9.12 Breathing in Other Animals
Fish — Gills
Water contains a small amount of dissolved oxygen. Fish cannot use lungs underwater, so they use gills. A fish gulps water through its mouth and pushes it out through the gill slits. As water flows past the feathery red gill filaments, oxygen seeps into the blood and carbon dioxide leaves.
Insects — Spiracles and Tracheae
An insect such as a cockroach or grasshopper has tiny holes along its body called spiracles. These open into a branching network of fine air tubes called tracheae, which carry air directly to every cell. Insects do not need blood to transport oxygen — the air reaches the cells themselves.
Frogs and Earthworms — Skin
A frog has simple lungs, but when it is underwater or resting, it breathes mainly through its moist skin. Gases dissolve in the thin film of mucus on the skin and pass straight into the blood vessels below. An earthworm has no lungs at all — it breathes entirely through its moist skin, which is why you will see earthworms only in damp soil. If its skin dries out, it dies.
| Animal | Respiratory organ | Lives in |
|---|---|---|
| Human, dog, cow, whale | Lungs | Land (whale surfaces to breathe) |
| Fish | Gills | Water |
| Cockroach, grasshopper | Spiracles & tracheae | Land |
| Frog | Lungs + moist skin | Land & water |
| Earthworm | Moist skin only | Damp soil |
| Amoeba | Whole cell surface | Pond water |
Activity 9.3 — Counting Your Breaths L3 Apply
You will need a stopwatch (or a phone timer) and a partner.
- Sit quietly for two minutes. Then count how many times you breathe in one minute (one inhale + one exhale = one breath). Record the value.
- Now do 20 jumping jacks. Immediately count your breaths for one minute again. Record.
- Rest for three minutes and count once more.
Predict: What will happen to your breathing rate after exercise? Why does the body change it, and why does it fall again after resting?
At rest, breathing rate is about 12–18 per minute. After exercise it can rise to 25–35 per minute because the muscles need more oxygen and produce more carbon dioxide. Once you rest, the body no longer needs so much oxygen, so the rate falls back to normal. Breathing rate is always linked to how hard the cells are working.
Competency-Based Questions
Apply & Reason — Respiration in Animals
During a school sports day, Kabir runs the 400-metre race. He crosses the finish line panting hard, with his legs aching. The PE teacher asks the class: "Why is Kabir breathing so fast, and why do his muscles ache?"
Q1. Kabir's muscles ache because of the build-up of which substance? L1
(b) Lactic acid. When oxygen cannot reach the muscles fast enough, anaerobic respiration produces lactic acid, which causes cramps and aching.
Q2. State two differences between breathing and cellular respiration. L2
(i) Breathing is a physical process (air in and out of lungs); cellular respiration is a chemical reaction inside cells. (ii) Breathing does not release energy by itself; cellular respiration releases the energy stored in glucose.
Q3. Why can an earthworm survive only in damp soil? L2
An earthworm breathes through its moist skin. Gases can only pass through the skin when it is wet. If the soil dries out, the worm's skin dries too, gas exchange stops, and the worm suffocates.
Q4. A fish taken out of water dies even though plenty of oxygen is around. Explain. L3
Fish gills are delicate feathery structures that work only when water keeps them spread out. In air they collapse and stick together, so very little surface is left for oxygen to enter the blood. The fish dies of suffocation, not from lack of oxygen in the air.
Q5. Amit learns that yeast carries out anaerobic respiration in dough. Write the word equation and explain why bread rises. L4
Yeast: Glucose → Alcohol + Carbon dioxide + small energy. The carbon dioxide gas released by yeast forms tiny bubbles inside the dough. These bubbles get trapped, and the dough swells up — that is why bread rises. During baking the alcohol evaporates and the bubbles expand further, giving the light, fluffy texture.
Assertion–Reason Questions
Choose: (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: Breathing rate increases during exercise.
R: Exercising muscles need more oxygen and produce more carbon dioxide.
(A) — both true, and R explains A. Faster breathing supplies extra O₂ and removes extra CO₂.
A: Insects do not need blood to carry oxygen to their cells.
R: The tracheal tubes of insects open directly onto each cell, so air reaches cells without going through blood.
(A) — both true, and R is the reason. This is why insects stay small — gases can only diffuse so far.
A: Aerobic respiration releases more energy than anaerobic respiration.
R: Aerobic respiration completely breaks down glucose using oxygen, while anaerobic respiration only partially breaks it down.
(A) — both true and R correctly explains A.
Frequently Asked Questions — Respiration in Animals
What does the topic 'Respiration in Animals' cover in Class 7 Science?
The topic 'Respiration in Animals' is part of NCERT Class 7 Science Chapter 9 — Life Processes in Animals. It covers the key ideas of respiration, breathing, lungs, gills, tracheae, diaphragm, inhalation, exhalation, explained through everyday examples, labelled diagrams and hands-on activities drawn from the NCERT Curiosity textbook. Students learn not just definitions but also the reasoning behind each concept so they can answer competency-based questions and assertion–reason items. The lesson helps Class 7 students build a strong base for higher classes by linking each idea to real observations at home, school and in nature, and by preparing them for CBSE school assessments and Olympiads.
Why is 'Respiration in Animals' important for Class 7 NCERT Science?
'Respiration in Animals' is important because it builds core scientific thinking that Class 7 students will use throughout middle and secondary school. NCERT Chapter 9 — Life Processes in Animals — introduces respiration and related ideas that appear again in Class 8, 9 and 10 Science. Mastering this subtopic helps students read labels and safety signs, understand news about science and technology, and perform better in CBSE school exams. The chapter also encourages curiosity and evidence-based thinking — skills that support the National Education Policy (NEP) 2020 focus on conceptual understanding and competency-based learning.
What are the key concepts students should remember from Respiration in Animals?
The key concepts in 'Respiration in Animals' for Class 7 Science are: respiration, breathing, lungs, gills, tracheae, diaphragm, inhalation, exhalation. Students should be able to define each term in their own words, give at least one everyday example, and explain how the concept connects to other chapters in NCERT Class 7 Science. For example, linking the idea to daily life — in the kitchen, classroom or outdoors — makes revision easier. Writing short notes, drawing labelled diagrams and solving the NCERT in-text and exercise questions for Chapter 9 will help students retain these concepts for unit tests and the annual CBSE examination.
How is Respiration in Animals taught using activities in NCERT Curiosity Class 7?
NCERT Curiosity Class 7 Science teaches 'Respiration in Animals' using an inquiry-based approach with Predict–Observe–Explain activities. Students are asked to make a guess first, then perform a simple experiment with safe, easily available materials, and finally explain what they observed. This matches the NEP 2020 focus on learning by doing. For Chapter 9 — Life Processes in Animals — the textbook includes hands-on tasks, labelled diagrams and questions that build Bloom's Taxonomy skills from Remember (L1) to Create (L6). Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding rather than rote memorisation.
What real-life examples of respiration can Class 7 students observe at home?
Class 7 students can observe respiration at home in many simple ways linked to 'Respiration in Animals'. Kitchens, school bags, playgrounds and the night sky are full of examples that connect to NCERT Chapter 9 — Life Processes in Animals. For instance, students can check labels on food and cleaning products, watch changes while cooking, or observe the Sun and Moon across a week. Keeping a small science diary — noting the date, what was observed and a quick sketch — turns everyday life into a science lab. These real-life connections make concepts stick and prepare students well for competency-based questions in CBSE Class 7 Science.
How does 'Respiration in Animals' connect to other chapters of Class 7 Science?
'Respiration in Animals' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of respiration appear again when students study related topics like heat, light, changes, life processes and Earth-Sun-Moon. For example, understanding this subtopic helps in building mental models for later chapters and for Class 8, 9 and 10 Science. Teachers often use cross-chapter questions in CBSE examinations to test whether students can apply what they learned in Chapter 9 — Life Processes in Animals — to new situations. This integrated approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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