Respiration in Organisms — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Respiration in Organisms" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 Science chapter "Respiration in Organisms" — 8 important questions with detailed answers for CBSE board…
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NCERT Solutions for Class 7 Science — Respiration in Organisms. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Respiration in Organisms — All 8 Questions Solved
Q1. Define respiration.
Respiration is the process by which organisms break down food (glucose) to release energy.
Formula: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy
Energy is used for all life activities.
Q2. What is aerobic respiration?
Aerobic respiration is the breakdown of glucose in the presence of oxygen.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 2,900 kJ energy
It occurs in mitochondria and releases more energy than anaerobic respiration.
Q3. What is anaerobic respiration? Give one example.
Anaerobic respiration is the breakdown of glucose in the absence of oxygen.
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy (in yeast)
Or C₆H₁₂O₆ → 2CH₃COOH + energy (in bacteria)
It releases less energy than aerobic respiration.
Q4. What happens to our muscles during sudden exercise?
During sudden exercise, muscles need more energy but oxygen supply is limited.
Muscles undergo anaerobic respiration to produce lactic acid.
Lactic acid accumulates causing muscle cramps or fatigue.
Deep breathing after exercise helps oxidise lactic acid.
Q5. Why do we breathe?
We breathe to take in oxygen and expel carbon dioxide.
Oxygen is essential for aerobic respiration in cells.
Respiration produces energy (ATP) required for all body functions.
Carbon dioxide is a waste product that must be removed.
Q6. Describe the process of breathing in humans.
Breathing has two phases:
1. Inhalation: Diaphragm contracts and moves down; intercostal muscles lift the ribcage; air enters the lungs
2. Exhalation: Diaphragm relaxes; intercostal muscles relax; ribcage falls; air is pushed out of lungs
Q7. What is the role of haemoglobin in respiration?
Haemoglobin is a protein present in red blood cells.
It has high affinity for oxygen and binds oxygen in the lungs.
It carries oxygen to all body tissues where oxygen is released for respiration.
It also carries some carbon dioxide back to the lungs.
Q8. Do plants respire? If yes, when do they respire?
Yes, plants respire continuously, both day and night.
During respiration, plants break down glucose to release energy for growth and maintenance.
At night, only respiration occurs (no photosynthesis).
During day, both photosynthesis and respiration occur simultaneously.
Respiration in Organisms — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the main purpose of respiration in living organisms?
- A. To produce food
- B. To release energy from food
- C. To remove waste materials
- D. To help in movement
Answer: B. To release energy from food — Respiration is a process where organisms break down food (glucose) to release energy that is essential for various life processes.
MCQ 2. Which gas do humans primarily inhale for respiration?
- A. Carbon dioxide
- B. Nitrogen
- C. Oxygen
- D. Hydrogen
Answer: C. Oxygen — Oxygen is vital for aerobic respiration, where it helps in the breakdown of glucose to release energy within the cells.
MCQ 3. What are the main products of aerobic respiration?
- A. Lactic acid and energy
- B. Alcohol, carbon dioxide, and energy
- C. Carbon dioxide, water, and energy
- D. Oxygen and glucose
Answer: C. Carbon dioxide, water, and energy — In aerobic respiration, glucose is completely broken down in the presence of oxygen to produce carbon dioxide, water, and a large amount of energy.
MCQ 4. Which of the following organisms breathes through its moist skin?
- A. Fish
- B. Bird
- C. Earthworm
- D. Human
Answer: C. Earthworm — Earthworms absorb oxygen directly through their moist skin and release carbon dioxide the same way, as their skin is permeable to gases.
MCQ 5. The process of taking in air rich in oxygen is called:
- A. Exhalation
- B. Inhalation
- C. Respiration
- D. Photosynthesis
Answer: B. Inhalation — Inhalation is the active physical process of drawing air, primarily oxygen, into the lungs.
MCQ 6. How is breathing different from respiration?
- A. Breathing involves only gas exchange, while respiration involves energy release.
- B. Breathing occurs only in lungs, while respiration occurs throughout the body.
- C. Breathing is a chemical process, while respiration is a physical process.
- D. Breathing uses carbon dioxide, while respiration uses oxygen.
Answer: A. Breathing involves only gas exchange, while respiration involves energy release. — Breathing is the physical process of inhaling and exhaling gases, whereas respiration is the biochemical process of breaking down food to release energy inside cells.
MCQ 7. What happens to the diaphragm during inhalation?
- A. It moves upwards
- B. It flattens and moves downwards
- C. It remains stationary
- D. It contracts and moves upwards
Answer: B. It flattens and moves downwards — During inhalation, the diaphragm contracts and flattens, moving downwards to increase the volume of the chest cavity, allowing air to rush in.
MCQ 8. Which part of a plant primarily facilitates gas exchange in leaves?
- A. Roots
- B. Stems
- C. Stomata
- D. Flowers
Answer: C. Stomata — Stomata are tiny pores on the surface of plant leaves that allow for the exchange of gases like oxygen and carbon dioxide with the atmosphere.
MCQ 9. When we exercise vigorously, our muscle cells sometimes respire anaerobically. What is produced during this process?
- A. Ethanol
- B. Carbon dioxide
- C. Lactic acid
- D. Water
Answer: C. Lactic acid — During intense exercise, when oxygen supply is insufficient, muscle cells respire anaerobically, producing lactic acid which can lead to muscle cramps.
MCQ 10. What is the role of gills in fish respiration?
- A. To absorb food from water
- B. To release carbon dioxide into the water and absorb oxygen
- C. To filter out impurities from water
- D. To help in swimming
Answer: B. To release carbon dioxide into the water and absorb oxygen — Gills are specialized organs in fish that extract dissolved oxygen from water and release carbon dioxide, a waste product, back into it.
MCQ 11. Why do roots of plants also respire, even though they are underground?
- A. To absorb water more efficiently
- B. To release energy for growth and absorption of minerals
- C. To perform photosynthesis in the dark
- D. To store food for the entire plant
Answer: B. To release energy for growth and absorption of minerals — Plant roots require energy for their growth, cell division, and active absorption of water and minerals, which is supplied through respiration using oxygen from soil air.
MCQ 12. If a person's breathing rate is 18 breaths per minute, approximately how many times does their diaphragm contract and relax in one hour?
- A. 18
- B. 108
- C. 1080
- D. 1800
Answer: C. 1080 — The diaphragm contracts and relaxes once per breath. So, 18 breaths/minute * 60 minutes/hour = 1080 times in one hour.
MCQ 13. Which of the following conditions would lead to anaerobic respiration in human muscle cells?
- A. Resting peacefully
- B. Performing light activities like walking
- C. Sprinting a 100-meter race
- D. Meditating
Answer: C. Sprinting a 100-meter race — Sprinting a 100-meter race requires a sudden burst of high energy, and the oxygen supply to muscles may not be sufficient, forcing them to respire anaerobically.
MCQ 14. Why are the walls of alveoli in the lungs extremely thin and richly supplied with blood vessels?
- A. To prevent infection
- B. To increase the rate of gas exchange
- C. To provide structural support to the lungs
- D. To keep the lungs moist
Answer: B. To increase the rate of gas exchange — The thin walls and rich blood supply of alveoli facilitate rapid and efficient diffusion of oxygen into the blood and carbon dioxide out of the blood.
MCQ 15. In yeast, what are the primary products when glucose is broken down in the absence of oxygen?
- A. Lactic acid and water
- B. Carbon dioxide and water
- C. Alcohol and carbon dioxide
- D. Oxygen and alcohol
Answer: C. Alcohol and carbon dioxide — Yeast performs anaerobic respiration, also known as fermentation, where glucose is broken down into alcohol (ethanol) and carbon dioxide, releasing a small amount of energy.
MCQ 16. Which of these is NOT a part of the human respiratory system?
- A. Lungs
- B. Trachea
- C. Stomach
- D. Nose
Answer: C. Stomach — The stomach is a primary organ of the digestive system, responsible for breaking down food, and is not involved in respiration.
MCQ 17. What causes a muscle cramp during heavy exercise?
- A. Accumulation of carbon dioxide
- B. Accumulation of lactic acid
- C. Accumulation of water
- D. Accumulation of oxygen
Answer: B. Accumulation of lactic acid — Muscle cramps often occur due to the build-up of lactic acid when muscles respire anaerobically during strenuous activity when oxygen is insufficient.
MCQ 18. The small openings on the sides of an insect's body, through which air enters and leaves, are called:
- A. Gills
- B. Lungs
- C. Stomata
- D. Spiracles
Answer: D. Spiracles — Insects have a network of tubes called tracheae that open to the outside through small pores known as spiracles, facilitating gas exchange.
MCQ 19. What gas do plants release during photosynthesis that is used by humans for respiration?
- A. Carbon dioxide
- B. Oxygen
- C. Nitrogen
- D. Water vapour
Answer: B. Oxygen — Plants produce oxygen during photosynthesis, which is an essential gas for aerobic respiration in humans and many other organisms.
MCQ 20. The air we breathe out is richer in which gas compared to the air we breathe in?
- A. Oxygen
- B. Nitrogen
- C. Carbon dioxide
- D. Water vapour
Answer: C. Carbon dioxide — During respiration, oxygen is consumed, and carbon dioxide is produced as a waste product, making exhaled air richer in carbon dioxide.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.