Chapter – 6 -Respiration in Organisms – Concepts included in the chapter –
- Why We Respire: Understanding the necessity of respiration in producing energy from food.
- Breathing and Its Process: Exploring how inhalation and exhalation occur and the role of organs like the diaphragm and ribs.
- Cellular Respiration: A look at how cells use oxygen to break down food, releasing energy.
- Aerobic and Anaerobic Respiration: Differentiating between respiration with and without oxygen.
- Breathing in Other Animals: How different animals, including insects, fishes, and birds, respire.
- Respiration in Plants: Understanding how plants breathe and perform gas exchange.
NCERT Exemplar Class 7 Science Chapter – 5-Physical and Chemical Changes- (Solved with detailed explanation)
Question 1 – Sometimes when we do heavy exercise, anaerobic respiration takes place in our muscle cells. What is produced during this process?
Options-
(a) alcohol and lactic acid
(b) alcohol and CO2
(c) lactic acid and CO2
(d) lactic acid only
- Answer- (d) lactic acid only
- Explanation- When we engage in heavy exercise, our muscles may not receive sufficient oxygen for aerobic respiration. As a result, the muscles switch to anaerobic respiration, which does not require oxygen. During anaerobic respiration in muscle cells, glucose is partially broken down into lactic acid. This process does not produce alcohol or CO2, thus making (d) lactic acid only, the correct answer.
Question 2- Yeast is used in wine and beer industries because it respires
Options-
(a) aerobically producing oxygen.
(b) aerobically producing alcohol.
(c) anaerobically producing alcohol.
(d) anaerobically producing CO2.
- Answer- (c) anaerobically producing alcohol.
- Explanation- Yeast cells can respire both aerobically and anaerobically. In the absence of oxygen, yeast undergoes anaerobic respiration, also known as fermentation. During fermentation, yeast converts sugars into alcohol (ethanol) and carbon dioxide. This process is crucial in the production of alcoholic beverages like wine and beer, making (c) anaerobically producing alcohol the correct choice.
Question 3- During the process of exhalation, the ribs move
Options-
(a) down and inwards.
(b) up and inwards.
(c) down and outwards.
(d) up and outward.
- Answer- (a) down and inwards.
- Explanation- During exhalation, the diaphragm relaxes and moves upwards, and the rib cage moves downwards and inwards. This action decreases the space in the chest cavity, increasing the pressure inside the lungs. As a result, air is pushed out of the lungs. Therefore, the correct answer is (a) down and inwards.
Question 4- Breathing is a process that
(i) provides O2 to the body.
(ii) breaks down food to release energy.
(iii) helps the body to get rid of CO2.
(iv) produces water in the cells.
Which of the following gives the correct combination of functions of breathing?
Options-
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)
- Answer- (c) (i) and (iii)
- Explanation- Breathing involves the intake of oxygen (O2) and the expulsion of carbon dioxide (CO2). Oxygen is vital for the body’s metabolic processes, including cellular respiration, where it helps in breaking down nutrients to release energy, but this process occurs at the cellular level and is not a direct function of breathing. Therefore, the correct combination that describes the functions of breathing is (i) providing O2 to the body and (iii) helping the body to get rid of CO2.
Question 5- Fish breathe with the help of gills which are richly supplied with blood vessels. The gills help the fish to
Options-
(a) take in oxygen from air.
(b) take in oxygen dissolved in water.
(c) absorb nutrients present in water.
(d) release waste substances in water.
- Answer- (b) take in oxygen dissolved in water.
- Explanation- Fish use gills to extract oxygen from water. Water containing dissolved oxygen passes over the gills, and oxygen is absorbed into the blood through capillaries in the gills. Thus, the correct answer is (b) take in oxygen dissolved in water.
Question 6 – Earthworms and frogs breathe through their skin because of which the skin of both the organisms is
Options-
(a) moist and rough.
(b) dry and rough.
(c) dry and slimy.
(d) moist and slimy.
- Answer- (d) moist and slimy.
- Explanation- Both earthworms and frogs respire through their skin, a process known as cutaneous respiration. For efficient gas exchange, their skin must remain moist. The moisture facilitates the diffusion of oxygen and carbon dioxide through the skin. Therefore, the correct answer is (d) moist and slimy.
Very Short Answer Questions
Question 7 – Mark the following statements as True or False. Correct the false statements.
(a) Oxygen breaks down glucose outside the cells of organisms.
- Answer- False
- Correction- Oxygen breaks down glucose inside the cells of organisms. During cellular respiration, oxygen is used within the cells to break down glucose, releasing energy, carbon dioxide, and water.
(b) Frogs can breathe through their skin as well as lungs.
- Answer- True
- Explanation- Frogs have the ability to breathe through their skin in addition to their lungs. This is particularly useful in diverse environments, both aquatic and terrestrial.
(c) Insects have spiracles on the lower surface of the body.
- Answer- False (Assuming based on standard biology knowledge)
- Correction- Insects typically have spiracles on the sides of their body. Spiracles are small openings that insects use for breathing. They lead to a network of air tubes called tracheae, which distribute air throughout the insect’s body.
(d) Exhaled air has more percentage of CO2 than inhaled air.
- Answer- True
- Explanation- During respiration, oxygen is taken into the body and used for cellular processes, while carbon dioxide, a waste product, is produced and removed from the body through exhalation. Therefore, exhaled air has a higher concentration of CO2 compared to inhaled air.
Question 8- Fill in the blanks with suitable words-
(a) The roots of a plant take up oxygen from the Air trapped between the soil particles.
- Explanation– In soil, there are tiny air spaces between the particles. Plant roots absorb oxygen from this air for their respiration.
(b) Diaphragm forms the floor of the chest cavity.
- Explanation– The diaphragm is a dome-shaped muscle located at the bottom of the chest cavity. It plays a crucial role in the process of breathing.
(c) Exchange of gases in the leaves take place with the help of stomata.
- Explanation– Stomata are tiny openings found mainly on the underside of plant leaves. They allow for the exchange of gases (oxygen and carbon dioxide) with the atmosphere.
(d) Cockroaches breathe with the help of air tubes called tracheae.
- Explanation- Insects like cockroaches have a network of air tubes called tracheae for respiration. These tubes deliver oxygen directly to the body cells and remove carbon dioxide.
Short Answer Questions
Question 9 – Pick the odd-one-out from each of the groups given below on the basis of respiratory organs. Give reason for your answer.
(a) Cockroach, grasshopper, snail, ant
Odd-one-out- Snail
Reason- The snail does not breathe by trachea whereas the cockroach, grasshopper, and ants breathe by the trachea.
(b) Lizard, cow, earthworm, snake
Odd-one-out- Earthworm
Reason- The earthworm breathes through its skin and does not have lungs.
(c) Crocodile, whale, dolphin, fish
Odd-one-out- Fish
Reason- Fish do not have lungs and breathe by their gills.
(d) Snake, tadpole, crow, goat
Odd-one-out- Tadpole
Reason- Tadpoles do not have lungs and breathe by their gills.
Question 10 – Which gas present in air is essential for aerobic respiration? What is the role of oxygen during respiration?
Answer- Atmospheric oxygen is essential for the process of aerobic respiration.During aerobic respiration, oxygen is used to break down glucose in the presence of oxygen, producing carbon dioxide, water, and energy. Oxygen acts as the final electron acceptor in the electron transport chain, a critical step in the process of energy generation in cells.
Question 11- On an average, an adult human being at rest breathes 15–18 times per minute. The breathing rate, however, may differ under different conditions. Arrange the following activities given in the box in order of increasing breathing rates and give a reason for your answer- sleeping, cycling, brisk walk, watching T.V.
Answer- Order- Sleeping > Watching T.V. > Brisk walk > Cycling
- Reason- The breathing rate increases with the level of physical activity. When a person is sleeping or watching TV, the physical activity is minimal, so the breathing rate is lower. During a brisk walk, the body requires more oxygen for the increased metabolic activity, leading to a faster breathing rate. Cycling, being more strenuous, demands even more oxygen, thus having the highest breathing rate among these activities.
Question 12 – On a very cold morning, Boojho and Paheli were talking with each other as they walked down to their school. They observed that the air coming out of their mouth looked like smoke. They were amused and wondered how it happened. Help them find the answer.
- Answer- When the climate is cold, the warm and moist air exhaled by us condenses into mist when it comes in contact with the cold air of the atmosphere. This mist looks like smoke and is more visible on cold mornings due to the significant temperature difference between the exhaled air and the surrounding atmosphere.
Question 13 – Whenever we feel drowsy or sleepy, we start yawning. Does yawning help us in any way?
- Answer- Yes, yawning does help us.When we feel sleepy, the rate of respiration in our body slows down, which can lead to a reduced supply of oxygen to our lungs. Yawning is a reflex that helps to bring extra oxygen into the lungs. This additional oxygen intake can help in making us more alert and awake.
Question 14 – Insects and leaves of a plant have pores through which they exchange gases with the atmosphere. Can you write two points of differences between these pores with respect to their position, number, and extension into the body?
- Differences-
- (i) Position– Spiracles are present on the sides of the insects’ body, while stomata are present on the lower surface of leaves.
- (ii) Number- Spiracles are fewer in number compared to stomata.
- (iii) Extension into the body- Spiracles lead to an extensive network of a tracheal system, which is absent in leaves.
Question 15 – Paheli participated in a 400 m race competition held at her school and won the race. When she came home, she had mixed feelings of joy and pain as she had cramps in her leg muscles. After a massage, she was relieved of the pain. Answer the following questions related to the situation-
(a) What can be the possible reasons for the pain in her legs?
- Answer- The pain in her legs might be because of the accumulation of lactic acid in her muscles.During heavy physical activity like running a 400 m race, muscle cells respire anaerobically due to insufficient oxygen supply. This anaerobic respiration produces lactic acid as a by-product, which can accumulate in the muscles and cause cramps or pain.
(b) Why did she feel comfortable after a massage?
- Answer- The massage gave her relief because it improves the circulation of blood. A massage helps in enhancing blood circulation, leading to an increased supply of oxygen to the muscle cells. This increased oxygen aids in the more complete breakdown of lactic acid into carbon dioxide (CO2) and water, thereby alleviating the muscle cramps and discomfort.
Question 16 – Observe Figure 10.1 carefully and answer the following questions-
(a) In which jar will the amount of CO2 be the highest and why?
- Answer- The amount of CO2 will be the highest in jar C. The reason for this is that the mice in Jar C will breathe out CO2, which results in the accumulation of CO2 in the jar.
(b) In which jar will the amount of CO2 be the lowest and why?
- Answer– The amount of CO2 will be the lowest in jar A.This is because the CO2 in jar A will be utilised by plants for photosynthesis, which involves taking in CO2.
Question 17 – Observe Figure 10.2 carefully and answer the following questions-
(a) Which process is being tested in the activity?
- Answer- This experiment is used to test the exhalation process during respiration.
(b) What is the result of the activity? Give reasons.
- Answer- Lime water turns milky in test tube B and test tube A remains unchanged.
- Reason- – This is because CO2 is present in the exhaled air, and when it reacts with lime water, it causes the lime water to turn milky, indicating the presence of carbon dioxide.
Question 18 – A food stall owner was preparing dough for making bhaturas. He added a pinch of yeast and sugar to the dough and left it in a warm place. After a few hours, the dough had risen. There was a sour smell too. Answer the following questions related to the situation-
(a) Why did the dough rise?
- Answer- CO2 produced by yeast during respiration makes the dough rise. Yeast cells respire anaerobically in the dough, producing carbon dioxide (CO2) as a by-product. The CO2 gas gets trapped in the dough, causing it to rise and expand.
(b) Why did the dough smell sour?
- Answer– During anaerobic respiration, yeast produces alcohol. This gives a sour smell to the dough.Along with CO2, alcohol is another by-product of anaerobic respiration in yeast. The alcohol contributes to the sour smell of the dough.
(c) Why was sugar added to the dough?
- Answer- Sugar acts as food for yeast. Yeast uses sugar as a source of energy. The sugar is broken down during anaerobic respiration to produce CO2 and alcohol.
(d) What would have happened if the dough was kept in the refrigerator soon after it was prepared?
- Answer- If kept in the refrigerator, yeast will not respire and multiply, and the dough will not rise and will not produce a sour smell. Low temperatures in the refrigerator inhibit the respiration and multiplication of yeast cells, preventing the production of CO2 and alcohol. This would result in the dough not rising and not developing a sour smell.
Question 19- Observe the figures given in Figure 10.3 (A) and (B) and answer the following-
(a) Which of the figures A or B indicates the process of inhalation and which is the process of exhalation?
- Answer- Figure (A) indicates inhalation and Figure (B) indicates exhalation. During inhalation, the diaphragm contracts and moves downwards, the chest cavity expands, and air is drawn into the lungs. This is depicted in Figure (A). During exhalation, the diaphragm relaxes and moves upwards, the chest cavity reduces in size, and air is expelled from the lungs, as shown in Figure (B).
(b) In the figure label the arrows and indicate the direction of-
- (i) Movement of air
- (ii) Movement of diaphragm
- (iii) Movement of ribs
Question 20 – Match the names of organisms in Column I with their organs of breathing given in Column II.
| Column I (Organisms) | Column II (Organs of breathing) |
| a) Butterflies | i) Lungs |
| b) Earthworms | ii) Gills |
| c) Sparrow | iii) Spiracles |
| d) Fish | iv) Skin |
Solution-
| Column I (Organisms) | Column II (Organs of breathing) |
| a) Butterflies | iii) Spiracles |
| b) Earthworms | iv) Skin |
| c) Sparrow | i) Lungs |
| d) Fish | ii) Gills |
Explanation-
- Butterflies breathe through spiracles, small openings on their body for gas exchange.
- Earthworms breathe through their skin, which must remain moist for effective gas exchange.
- Sparrows, being birds, breathe using their lungs.
- Fish have gills that allow them to extract oxygen from water.
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