Respiration — REET Level 2 Science Notes
This page covers respiration for REET Level 2 Science — the difference between breathing and respiration, aerobic-anaerobic respiration, and the respiratory organs of different organisms — in exam-focused form. REET 2024 asked a process-level question on this topic, so glycolysis-level detail is included too.
- 1 question in REET 2024
- Class 6-8 level content
- 6 min read
How REET actually asks this topic
REET 2024 carried a fairly in-depth question on this topic — which molecule forms in the first step of glucose breakdown (pyruvate). In other words, REET doesn't stop at the basic breathing-versus-respiration distinction here; it also tests process-level understanding of glycolysis. This page covers both levels — the basic definitions and the step-by-step process — and also includes the respiratory organs of various organisms, so the whole topic is available in one place.
The difference between breathing and respiration
Breathing is simply the physical exchange of air into and out of the body — taking in oxygen in the lungs and releasing carbon dioxide. It is purely a mechanical action, with no chemical reaction involved.
Respiration is a much broader chemical process that happens inside the cell, in which glucose is broken down to release energy. Breathing is only one part of this whole process, not the entire thing. The energy released by respiration is used for every activity of the body — growth, movement, digestion, and more.
Respiration is not limited to animals; plants also respire continuously, day and night, whereas photosynthesis happens only during the day, in sunlight. In plants, gas exchange happens through the stomata on leaves, the lenticels on the stem, and the root hairs — being able to identify each of these organs separately is useful for the classification-based questions REET sometimes asks.
Types of respiration and their products
| Step / type | Location | Reactants → products |
|---|---|---|
| Glycolysis (common first step) | Cytoplasm | Glucose → pyruvate (this step is identical in both types of respiration) |
| Aerobic respiration | Mitochondria | Pyruvate + oxygen → carbon dioxide + water + more energy |
| Anaerobic respiration — in yeast | Cytoplasm | Pyruvate → ethanol (alcohol) + carbon dioxide + less energy |
| Anaerobic respiration — in human muscles (during intense exercise) | Cytoplasm | Pyruvate → lactic acid + less energy (causes fatigue/cramps) |
REET 2024 asked directly about the first product of glycolysis (pyruvate); remember that glycolysis is identical in both types of respiration — only the pathway after it depends on whether oxygen is available.
Aerobic vs anaerobic respiration — a quick comparison
- Need for oxygen
- Required in aerobic respiration; not required in anaerobic respiration
- Location
- Aerobic — mitochondria; anaerobic — cytoplasm only
- Energy produced
- Aerobic respiration releases more energy; anaerobic releases comparatively less
- Final products
- Aerobic — CO₂ and water; anaerobic — ethanol+CO₂ (in yeast) or lactic acid (in muscles)
Respiratory organs of different organisms
- Humans
- Lungs
- Fish
- Gills — a structure specially adapted to absorb oxygen dissolved in water
- Earthworm
- Gas exchange through its moist skin
- Insects (such as a cockroach)
- Tracheae (breathing tubes), with air entering through spiracles on the body
- Frog
- Through its moist skin in water and through its lungs on land — respiration through both media
Breathing rate and a simple test
At rest, a normal adult's breathing rate is roughly 15-18 breaths per minute. This rate rises during exercise or exertion, because the muscles need more energy, which in turn requires more oxygen and glucose.
A simple classroom test can show that exhaled air contains more carbon dioxide than inhaled air — when exhaled air is blown into limewater, it turns milky faster than when inhaled air is blown into it.
Every cell in the body uses the energy released by respiration according to its own needs — muscles for movement, the brain for thinking, and growing tissue for building new cells. This is exactly why respiration is counted among life's most essential processes, and its stopping is taken as a sign of death.
How to teach this to children
Classroom activity
Have students count their normal breathing rate for 1 minute, then have them run for 1 minute and count again, and discuss the difference. The results can be recorded in a table on the board and shared with the whole class.
Teaching aids
Run the simple limewater experiment in class so children can directly see carbon dioxide production. Two test tubes can be used to blow in inhaled and exhaled air respectively, and the speed at which each turns milky can be compared.
Common misconception
Many students take breathing and respiration to be the same thing; make it clear that breathing is only the physical exchange of gases, while respiration is the chemical process of releasing energy inside the cell. Also make it clear that plants respire continuously too, even though they have no lungs.
Assessment idea
Ask students, 'why do your legs cramp after running?' — a correct answer checks understanding of lactic acid build-up. You can also check understanding of anaerobic respiration's products (ethanol) using the example of yeast.
Memory trick
Glycolysis always makes pyruvate first — whether or not oxygen is present; it's the shared first step of both types of respiration. Only after that does the path diverge — with oxygen, it goes to CO₂ and water in the mitochondria; without it, to ethanol or lactic acid. In short, remember: 'pyruvate first, then oxygen decides the rest of the route'.
REET 2024 question (with solution)
Question 124
During respiration which molecule is formed in the first step of break down of glucose.
- Aइथेनॉल
- Bपायरुवेट
- Cलैक्टिक अम्ल
- Dकार्बन-डाइऑक्साइड
Explanation
श्वसन के पहले चरण ग्लाइकोलाइसिस में, जो कोशिकाद्रव्य में होता है, ग्लूकोस (6 कार्बन) टूटकर पायरुवेट (3 कार्बन) के दो अणु बनाता है। इसके बाद ऑक्सीजन की उपस्थिति/अनुपस्थिति के अनुसार पायरुवेट से CO₂ और जल, इथेनॉल या लैक्टिक अम्ल बनते हैं, इसलिए ये पहले चरण के उत्पाद नहीं हैं।
Practice questions
Question 1
Where does the first reaction of glucose breakdown during respiration (glycolysis) take place?
- Aमाइटोकॉन्ड्रिया
- Bकोशिकाद्रव्य (cytoplasm)
- Cकेन्द्रक (nucleus)
- Dकोशिका भित्ति
Explanation
Glycolysis happens in the cytoplasm, and it's the shared first step of both aerobic and anaerobic respiration.
Question 2
Aerobic respiration occurs in the presence of which of the following?
- Aकार्बन डाइऑक्साइड
- Bऑक्सीजन
- Cनाइट्रोजन
- Dजल
Explanation
Aerobic respiration happens in the mitochondria in the presence of oxygen, and it releases more energy.
Question 3
Which product is formed by anaerobic respiration in Yeast?
- Aलैक्टिक अम्ल
- Bएथेनॉल व कार्बन डाइऑक्साइड
- Cकेवल जल
- Dकेवल ऑक्सीजन
Explanation
In yeast, anaerobic respiration (alcoholic fermentation) produces ethanol and carbon dioxide, which is useful in the baking industry.
Question 4
The main cause of muscle cramps in humans during intense exercise is
- Aग्लूकोस की अधिकता
- Bलैक्टिक अम्ल का जमाव
- Cऑक्सीजन की अधिकता
- Dएथेनॉल का बनना
Explanation
When muscles don't get enough oxygen, they produce lactic acid through anaerobic respiration, and its build-up causes cramps and fatigue.
Question 5
If a teacher wants students to understand through their own experience why the breathing rate increases after exercise, the most suitable classroom activity is
- Aकेवल परिभाषा रटवाना
- Bव्यायाम से पहले व बाद की श्वसन दर गिनवाना
- Cचित्र दिखाना
- Dप्रश्नोत्तर पुस्तिका हल कराना
Explanation
Directly counting the breathing rate before and after exercise lets children understand, through their own experience, the link between energy demand and breathing rate.
Question 6
Which sequence correctly represents the stages of aerobic respiration?
- Aग्लूकोस → पायरुवेट → कार्बन डाइऑक्साइड + जल + ऊर्जा
- Bग्लूकोस → एथेनॉल → पायरुवेट
- Cपायरुवेट → ग्लूकोस → कार्बन डाइऑक्साइड
- Dग्लूकोस → लैक्टिक अम्ल → पायरुवेट
Explanation
In aerobic respiration, glucose first breaks down into pyruvate (glycolysis), and then in the mitochondria, in the presence of oxygen, it forms carbon dioxide, water and energy.
Question 7
In an earthworm, exchange of gases mainly takes place through
- Aफेफड़े
- Bगलफड़े
- Cनम त्वचा
- Dश्वास नलिकाएँ
Explanation
An earthworm exchanges oxygen and carbon dioxide mainly through its moist skin.
Question 8
Lime water quickly turns milky when a person breathes out into it. This indicates an excess of which gas?
- Aऑक्सीजन
- Bनाइट्रोजन
- Cकार्बन डाइऑक्साइड
- Dहाइड्रोजन
Explanation
Exhaled air contains more carbon dioxide than inhaled air, which is why it turns limewater milky faster.
Question 9
Which of the following statements is FALSE?
- Aग्लाइकोलिसिस वायवीय व अवायवीय दोनों श्वसन में होती है
- Bवायवीय श्वसन में अवायवीय की तुलना में अधिक ऊर्जा मुक्त होती है
- Cअवायवीय श्वसन माइटोकॉन्ड्रिया में होता है
- Dमानव पेशियों में अवायवीय श्वसन से लैक्टिक अम्ल बनता है
Explanation
Anaerobic respiration happens in the cytoplasm, not the mitochondria; the mitochondria are needed only for aerobic respiration.
Question 10
To clarify the difference between "breathing" and "respiration" in class, which example would a teacher give as the most suitable?
- Aनाक से हवा अंदर-बाहर करना बनाम कोशिका में ऊर्जा-मुक्ति की प्रक्रिया
- Bकेवल फेफड़ों का चित्र दिखाना
- Cश्वसन दर गिनवाना
- Dकोई अंतर नहीं है, यह समझाना
Explanation
Comparing the physical exchange of air through the nose (breathing) with the release of energy inside the cell (respiration) helps children clearly understand the difference between the two processes.
Frequently asked questions
What is the difference between breathing and respiration?+
Breathing is just the physical exchange of air in the lungs, while respiration is the entire chemical process of releasing energy inside the cell by breaking down glucose — respiration is much broader than breathing.
Where does anaerobic respiration occur?+
Anaerobic respiration happens in yeast (alcoholic fermentation, useful in bread and the alcohol industry) and in human muscles during intense exercise (producing lactic acid).
Where does lactic acid form, and why?+
During intense exercise, when muscles don't get enough oxygen, they carry out anaerobic respiration and turn pyruvate into lactic acid, which causes cramps and fatigue. This acid gradually clears with rest, and the pain eases.
What level of question does REET ask on respiration?+
Based on REET 2024, this topic can go all the way down to process-level detail like glycolysis, not just definitions — so it's important to understand every step of both the aerobic and anaerobic pathways.
What is a normal adult's resting breathing rate?+
Roughly 15-18 breaths per minute, which increases in situations like exercise, fever, or being at high altitude.
Do plants respire too?+
Yes, plants respire continuously, day and night, while photosynthesis happens only during daylight hours — these are two different processes, and REET often pairs them to create confusion.
What is the energy released by respiration used for?+
The energy released by respiration is used for all of the body's activities — movement, growth, digestion, and thinking — which is why it's considered a fundamental life process.
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Change Log
- 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked