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Q1. Why do living organisms respire?
Respiration is the process by which living organisms break down food to release energy. This energy is essential for all life processes such as growth, movement, and maintaining body temperature. Organisms do not respire to produce food, absorb carbon dioxide, or digest nutrients—those are separate processes.
Q2. What is the main purpose of cellular respiration?
The main purpose of cellular respiration is to break down food (glucose) inside cells to release energy in the form of ATP. Breathing involves inhaling/exhaling, and blood transport is circulation. The energy released is used for various cellular activities.
Q3. Which gas is taken in during aerobic respiration?
In aerobic respiration, oxygen is taken in from the environment. This oxygen is used to break down glucose completely into carbon dioxide and water, releasing a large amount of energy. Carbon dioxide is released as a waste product, not taken in.
Q4. What are the final products of aerobic respiration?
The final products of aerobic respiration are carbon dioxide (CO₂), water (H₂O), and a large amount of energy (in the form of ATP). Glucose and oxygen are the reactants. Alcohol and lactic acid are products of anaerobic respiration.
Q5. In which part of the cell does aerobic respiration mainly occur?
Aerobic respiration mainly occurs in the mitochondria, which are often called the “powerhouses” of the cell. The mitochondria contain enzymes that help break down food using oxygen to release energy. The cytoplasm is involved in the initial steps of respiration, but the main aerobic process occurs in mitochondria.
Q6. What does “anaerobic respiration” mean?
Anaerobic respiration is the breakdown of food (glucose) without using oxygen. It occurs in some bacteria, yeast, and sometimes in human muscle cells during intense exercise. It produces less energy compared to aerobic respiration.
Q7. During anaerobic respiration in yeast, glucose is converted into:
In yeast, anaerobic respiration (fermentation) converts glucose into ethanol (alcohol), carbon dioxide, and a small amount of energy. This process is used in baking and brewing. Lactic acid is produced in human muscles during anaerobic respiration.
Q8. What causes the puffed-up appearance of dough used for making bread or idli?
Yeast produces carbon dioxide gas during anaerobic respiration. This gas gets trapped in the dough, causing it to rise and become fluffy. This is why bread and idli become soft and puffed up.
Q9. During heavy exercise, why do our muscles sometimes feel painful or get cramps?
During heavy exercise, muscles may not get enough oxygen, so they switch to anaerobic respiration. This produces lactic acid, which accumulates in muscles and causes pain and cramps. Lactic acid is the waste product in this process.
Q10. Which of the following organisms are known as anaerobes?
Anaerobes are organisms that can survive and grow without oxygen. Some are obligate anaerobes (cannot tolerate oxygen), while others are facultative anaerobes (can survive with or without oxygen). Organisms that need oxygen are called aerobes.
Q11. The energy released during the breakdown of food is stored in a special molecule called:
ATP (adenosine triphosphate) is the energy currency of the cell. The energy released from the breakdown of food is stored in ATP molecules. When cells need energy, ATP is broken down to release it. DNA and RNA are genetic materials, and RBC stands for red blood cells.
Q12. Which process is the exact opposite of respiration?
Photosynthesis is the process by which green plants use carbon dioxide and water to produce glucose and oxygen using sunlight. This is the opposite of respiration, which uses oxygen and glucose to produce carbon dioxide, water, and energy. The equations are reversed.
Q13. What is the common name for the process of taking in air rich in oxygen and giving out air rich in carbon dioxide?
Breathing is the physical process of inhaling air rich in oxygen and exhaling air rich in carbon dioxide. Respiration is the cellular process of breaking down food to release energy. Breathing is the mechanical process, while respiration is chemical.
Q14. During inhalation, the size of the chest cavity:
During inhalation, the diaphragm contracts and moves downward, and the ribs move upward and outward. This increases the volume of the chest cavity, reducing the air pressure inside the lungs, and air rushes in.
Q15. During exhalation, the diaphragm becomes:
During exhalation, the diaphragm relaxes and moves upward, returning to its dome-shaped position. This decreases the volume of the chest cavity, increasing air pressure, and air is pushed out of the lungs. During inhalation, it becomes flat.
Q16. What is a normal breathing rate for a healthy adult human at rest (breaths per minute)?
The normal breathing rate for a healthy adult at rest is about 12 to 20 breaths per minute. This rate can vary with age, activity, and health. Children have a higher rate, and athletes may have a lower resting rate.
Q17. Why does your breathing rate increase after running a race?
During exercise, muscles work harder and need more energy. This requires more oxygen for aerobic respiration. The increased breathing rate supplies more oxygen to the body and removes the extra carbon dioxide produced.
Q18. Which gas is released as a waste product during respiration in humans?
During respiration, carbon dioxide is released as a waste product. It is transported from the tissues to the lungs and exhaled. Oxygen is used up in the process, carbon monoxide is not produced (it is a pollutant), and nitrogen is not involved in respiration.
Q19. The breakdown of glucose in the cytoplasm of a cell without using oxygen is called:
Glycolysis is the process of breaking down glucose in the cytoplasm without using oxygen. It is the first step of both aerobic and anaerobic respiration. The Krebs cycle occurs in mitochondria and requires oxygen, photosynthesis is in plants, and transpiration is water loss.
Q20. Which of the following organisms uses anaerobic respiration to produce alcohol?
Yeast is a single-celled fungus that performs anaerobic respiration (fermentation) to produce alcohol (ethanol) and carbon dioxide. This process is used in brewing and baking. Humans produce lactic acid during anaerobic respiration, and plants and fish primarily use aerobic respiration.
Q21. If you hold your breath for a few seconds, what makes you feel the urge to breathe again?
The urge to breathe is triggered mainly by the buildup of carbon dioxide in the blood, not by a lack of oxygen. The brain detects the increase in CO₂ levels and signals the breathing muscles to contract. This is why holding your breath becomes uncomfortable.
Q22. Which muscle is the main muscle involved in breathing?
The diaphragm is the main muscle involved in breathing. It is a dome-shaped muscle at the base of the chest cavity. It contracts and flattens during inhalation, increasing chest volume. The biceps, triceps, and quadriceps are limb muscles, not involved in breathing.
Q23. When we exhale, the air we breathe out is warmer than the air we breathed in. Why?
The air we exhale is warmer because it has been warmed by the body’s internal temperature (about 37°C). The air passes through the warm respiratory passages, where it picks up heat. The lungs do not produce heat independently; the body’s overall temperature warms the air.
Q24. Why do we often see a doctor putting a stethoscope on a patient’s chest?
A stethoscope is used to listen to internal body sounds, especially the heartbeat and breathing (lung) sounds. This helps doctors detect abnormalities. Blood pressure is measured with a sphygmomanometer, fever with a thermometer, and injections are given with syringes.
Q25. Which of the following is a characteristic of anaerobic respiration?
Anaerobic respiration produces much less energy compared to aerobic respiration because glucose is not completely broken down. It does not require oxygen, and it does not produce water as a byproduct (lactic acid or alcohol is produced instead).
Q26. During aerobic respiration, one molecule of glucose releases approximately how much energy compared to anaerobic respiration?
Aerobic respiration releases a much larger amount of energy (about 36-38 ATP molecules per glucose) compared to anaerobic respiration (which releases only 2 ATP molecules per glucose). This is because glucose is completely broken down in aerobic respiration.
Q27. Which of the following is an example of an anaerobe?
Clostridium bacteria are anaerobes that thrive in oxygen-deprived environments like deep mud, soil, and the intestines. Humans, mango trees, and eagles are aerobes that require oxygen for respiration.
Q28. Why do we sometimes yawn?
Yawning is believed to be a reflex that helps the body take in a large amount of oxygen when carbon dioxide levels rise or oxygen levels drop. It may also help cool the brain. It is not just a sign of tiredness; it has a physiological function.
Q29. The process of breakdown of food to release energy takes place:
Respiration occurs in every living cell of the body. Cells use oxygen to break down glucose and release energy. The lungs, stomach, and heart are not the sites of respiration; they serve other functions. Mitochondria inside cells are the main sites of aerobic respiration.
Q30. What happens to the breathing rate when a person is sleeping?
During sleep, the body’s metabolic rate decreases, so less oxygen is needed. The breathing rate slows down compared to when the person is awake and active. It does not stop or become irregular, though some sleep disorders may cause irregularities.
Q31. Which of the following is NOT a product of any type of respiration?
Oxygen is not a product of respiration; it is a reactant used in aerobic respiration. The products of respiration are energy (ATP), carbon dioxide, and water (in aerobic respiration). Oxygen is consumed, not produced, during respiration.
Q32. The tiny air sacs present in the lungs where exchange of gases takes place are called:
Alveoli are tiny, balloon-like air sacs in the lungs where the exchange of oxygen and carbon dioxide occurs. They have a large surface area and thin walls, which facilitate efficient gas exchange. Bronchi, trachea, and bronchioles are air passages, not sites of gas exchange.
Q33. In which form is carbon dioxide mainly transported from body tissues to the lungs?
Most carbon dioxide is transported in the blood in the form of bicarbonate ions (HCO₃⁻). A small amount is dissolved in plasma, and some is attached to hemoglobin. The bicarbonate form is the main transport mechanism.
Q34. If a person is doing yoga and breathing slowly and deeply, what effect does it have on the breathing rate?
Slow, deep breathing reduces the number of breaths per minute because each breath takes longer. Although the rate decreases, the volume of air exchanged may be similar or even greater. This is often practiced in yoga for relaxation and improved oxygen exchange.
Q35. The process of respiration by yeast is used in the baking industry because it produces:
Yeast produces carbon dioxide gas during fermentation, which causes dough to rise and become fluffy. Although alcohol is also produced, it evaporates during baking. The carbon dioxide is what gives bread its soft, puffy texture.
Q36. Which of the following animals has a breathing rate much higher than humans?
Small animals like birds (e.g., sparrows) have much higher breathing rates than humans because they have a higher metabolic rate and lose heat faster due to their small size. Elephants and whales have slower rates, and tortoises have very slow rates.
Q37. During cellular respiration, what is the role of hemoglobin?
Hemoglobin is a protein in red blood cells that binds to oxygen in the lungs and carries it to tissues throughout the body. It also helps transport some carbon dioxide back to the lungs. It does not digest food, fight germs, or clot blood.
Q38. Which of the following statements is true about breathing?
Breathing is a physical process that involves the movement of air into and out of the lungs. It is a mechanical process. Respiration (the cellular process) is chemical and produces energy. Breathing involves both inhalation and exhalation.
Q39. What is the correct order of air passage in humans during inhalation?
The correct pathway during inhalation is: air enters through the nostrils → passes through the trachea (windpipe) → enters the bronchi → then into the bronchioles → finally reaches the alveoli in the lungs. The other options have incorrect order.
Q40. Why do deep-sea divers carry oxygen cylinders?
Underwater, there is no free oxygen to breathe. Deep-sea divers carry oxygen cylinders to supply the oxygen needed for respiration. The cylinders also contain other gases to prevent decompression sickness. Staying warm and seeing clearly are not the primary reasons.
Q41. A person who is jogging has a breathing rate of 25 breaths per minute. After resting for 10 minutes, his rate drops to 15. This happens because:
After rest, the muscles no longer need as much oxygen because the demand for energy has decreased. The breathing rate slows down to match the reduced need for oxygen. The body still needs energy, but less is required at rest.
Q42. Which of the following is a waste product of anaerobic respiration in human muscles?
In human muscles, anaerobic respiration produces lactic acid as a waste product when oxygen is insufficient. This lactic acid causes muscle fatigue and cramps. Ethanol is produced by yeast, and carbon dioxide is produced in aerobic respiration.
Q43. The number of times a person breathes in one minute is called:
The number of breaths taken per minute is called the breathing rate. Pulse rate is the number of heartbeats per minute, heart rate is another term for pulse, and respiration rate is sometimes used interchangeably with breathing rate but refers to the cellular process as well.
Q44. What happens to the diaphragm when you inhale deeply?
During deep inhalation, the diaphragm contracts and moves downward, increasing the volume of the chest cavity. This creates negative pressure, drawing air into the lungs. When it relaxes (exhalation), it moves upward to its dome shape.
Q45. Insects like grasshoppers respire through tiny holes on their body called:
Insects respire through tiny openings called spiracles on their body surface. Air enters through these spiracles and travels through a network of tubes called tracheae to reach cells. Gills are used by aquatic animals, lungs are in vertebrates, and skin is used by some animals like earthworms.
Q46. Which of the following is NOT a characteristic of a good respiratory surface (like alveoli)?
A good respiratory surface must be thin and moist to allow efficient gas exchange, have a large surface area, and have a rich blood supply. Thick and dry surfaces would impede diffusion of gases. Alveoli are thin, moist, and well-supplied with blood.
Q47. Which type of respiration is more efficient and why?
Aerobic respiration is more efficient because it completely breaks down glucose, releasing much more energy (36-38 ATP) compared to anaerobic respiration (2 ATP). Although anaerobic respiration is faster, it is less efficient in terms of energy yield.
Q48. The process of respiration by yeast is used in the wine industry to produce:
Yeast is used in the wine industry to produce alcohol (ethanol) through anaerobic respiration (fermentation). The alcohol is the desired product for wines and beers. Carbon dioxide is also produced but is a byproduct, and lactic acid is produced by bacteria in other processes.
Q49. If a person has a fever, how does it affect their breathing rate?
During a fever, the body’s metabolic rate increases, which raises the demand for oxygen. This leads to an increased breathing rate to supply more oxygen and remove the extra carbon dioxide produced. The body works harder to maintain homeostasis.
Q50. In which of the following situations would a person’s breathing rate be the slowest?
A person’s breathing rate is slowest during sleep when the body is at rest and energy demand is lowest. Playing football, climbing stairs, and running a marathon are all forms of physical activity that increase the need for oxygen and thus increase the breathing rate.