Monday , August 10 2020
7th Class CBSE Science NCERT Book

Respiration in Organisms: 7th NCERT CBSE Science Ch 10

Respiration in Organisms 7th Class NCERT CBSE Science Chapter 10

Question: What are the end products of aerobic respiration.

Answer: During aerobic respiration, carbon dioxide and water are released along with a large amount of energy.

Question: The cellular respiration process takes place in which cell organelle?

Answer: Cellular respiration takes place in the mitochondria of the cell.

Respiration in Organisms NCERT – Question: Name the end products of anaerobic respiration in yeast.

Answer: The end product formed during anaerobic respiration in yeast are

  1. Ethyl alcohol
  2. Carbon dioxide
  3. Energy

Question: In some animals, exchange of gases takes place through its thin and moist skin. Name one such animal.

Answer: Earthworm is an animal where exchange of gases during breathing or respiration takes place through its thin and moist skin.

Question: Give the name of respiratory organs in following animals.

  1. Fish
  2. Human being

Answer: The respiratory organ of the following animals are as follows

  1. Fish – Gills
  2. Human being – lungs

Question: Our nostrils has hair and mucous. What is the need to have them in our nasal cavity?

Answer: Our nostrils possess hairs and mucous lining. These help in preventing dirt, dust and germs from entering our respiratory system.

Respiration in Organisms NCERT – Question: Sometimes we see that farmers loosen the soil. What is the reason behind it?

Answer: The farmers sometimes loosen the soil. This helps the root to respire through the air present in the space between soil particles.

Question: Various organs constitute the respiratory system of human. These organs are located according to their functions. Identify them.

Answer: The various organs in the respiratory system of human are nostrils, nasal passage, nasal cavity, windpipe and lungs.

Question: The vocal ability of humans is the responsibility of an organ commonly known as voice box. What is its scientific name?

Answer: The organ that is responsible for speech is larynx or voice box. It lies between pharynx and trachea.

Respiration in Organisms NCERT – Question: What changes are observed in diaphragm during inhalation?

Answer: During the process of inhalation diaphragm contracts and moves downwards.

Respiration in Organisms NCERT – Question: When we exhale or breathe out, percentage of a certain gas is high. Name the gas.

Answer: The gas, carbon dioxide is in higher percentage or amount, when we exhale or breathe out.

Question: In the experiment, where we exhale into lime water containing glass. What changes were observed by you?

Answer: When we exhale into lime water its colour changes, into slightly milky white because exhaled air contains CO2.

Question: Insects have a special organ present to carry out respiration. What is that organ called?

Answer: Insects possess special organ called spiracles for respiration.

Respiration in Organisms NCERT – Question: Name the respiratory organs in frogs.

Answer: Frogs respire through their moist skin as well as through a pair of lungs.

Question: Certain small pores are present on the surface of plant through which gaseous exchange occurs. Identify these pores?

Answer: Stomata are the tiny pores that are present on the surface of plant through which gaseous exchange occurs.

Respiration in Organisms NCERT – Question: What happens to your breathing rate when you

  1. exercise
  2. go to sleep

Answer: The breathing rate during exercise is increased while during sleep it goes down.

Question: Floor of chest cavity refers to which organ of respiration?

Answer: Diaphragm is known as the floor of chest cavity.

Question: Respiration is a continuous process. What is the need for it to be continuous rather than being like photosynthesis?

Answer: Process of respiration yields energy which is required to perform a variety of routine activities. Thus, it needs to be a continuous process.

Question: A part from stomata another structure is used by plants to respire. Name that structure.

Answer: Lenticels

Question: Name the organisms which respire using anaerobic mode. Give an example of ane such organism.

Answer: Anaerobes respire using anaerobic mode. Yeast is an organism respiring anaerobically.

Respiration in Organisms NCERT – Question: Explain cellular respiration.

Answer: The process of breakdown of food in the cell with the release of energy is called cellular respiration.

Question: All organisms breathe in O2 and CO2. Should be less O2 and excess of CO2 in our environment.

Answer: The CO2 released by us is used by plants during the process of respiration and they release O2 as a result of this process which is used by rest of the organisms.

Question: The process of fermentation is based on which principle?

Answer: Anaerobic respiration.

Question: When oxygen enters our body it combines with haemoglobin to form a new substance. What is that new product.

Answer: Oxyhaemoglobin.

Respiration in Organisms NCERT – Question: Is the rate of breathing same for all the respiring organism?

Answer: No, different organisms respire at different rate because they all perform different activities at all times.

Question: Which gas present in air is essential for aerobic respiration? What is the role of this gas during respiration?

Answer: Oxygen present in air is essential for aerobic respiration. Oxygen breaks down food and releases energy during respiration.

Question: 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 assumed and wondered how it happened. Help them to find the answer.

Answer: On a cold day, the warm and moist air exhaled by us condenses into moist when it comes in contact with the cold air of the atmosphere, this looks like white smoke.

Question: Pick the odd one out from each of the groups given below on the basis of respiratory organs. Give reason for your answer.

  1. Cockroach, grasshopper, snail, ant
  2. Lizard, cow, earthworm, snake
  3. Crocodile, whale, dolphin, fish
  4. Snake, tadpole, crow, goat


  1. Snail, as it does not breathe by means of trachea.
  2. Earthworm, because it breathes through its skin and it does not have lungs.
  3. Fish, as most fish breathe through their gills and do not have lungs.
  4. Tadpole, as it breathes through gills and do not have lungs.

Question: 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?

Answer: Pores present on the sides of insects are called spiracles while pores present on the surface of leaves are called stomata. These structures are responsible for the exchange of gases with the atmosphere.
Differences between these two are as follows

  • Spiracles are fewer in number as compared to stomata.
  • Spiracles lead to an extensive network of tracheal system which is absent in the leaves.

Question: Frogs are amphibians. They survive on land and water, do they have any respiratory issue? How does frog breathe when they are in water? Do they possess lungs? Explain the role of lungs in frogs.

Answer: Frog breathe by their moist skin and through lungs also. So, they do not have any, respiratory issue.
When frog enters into water, the skin of frog helps in respiration.

The oxygen rich air enters through the skin. When the frog is on land, a pair of lungs helps in respiration.

The lungs take the oxygen rich air through the nostrils from where the oxygen is absorbed by the blood and carried throughout the body. The carbon dioxide from the blood is diffused back through the skin and lungs into the atmosphere.

Respiration in Organisms NCERT – Question: After we work hard or perform physical activity, we feel hungry. Explain why.

Answer: When we work hard or perform physical activity (like running, swimming, cycling), we need more energy. To fulfill the energy requirement, we breathe faster. Fast breathing helps in supply of more oxygen to our cells. Due to this, rate of breakdown of food increases and more energy is released. The rapid breakdown of food makes us to feel more hungry.

Question: Name one organism who respires anaerobically. How does this organism help in beverage and baking industry?

Answer: Yeast is a single celled organism. During anaerobic respiration (also called fermentation), yeast produces ethanol or alcohol as a byproduct which is used in making wine and beer. The carbon dioxide produced by yeast is used in the bread making industry. The CO2 gas released during this process causes the bread dough to rise.

Question: Smoking is considered harmful due to certain effects. Explain in brief.

Answer: Lungs are very delicate organs and essential for breathing, thus beeping us alive. Smoking tobacco in the form of beedi, cigarette or cigar damages our lungs gradually and causes ill health. While smoking, smoke along with chemicals present in tobacco enters our body. These chemicals present in tobacco damages the lungs in many ways tike breathing becomes difficult causes lung cancer, heart diseases, etc. Smoking also affects people around smokers as they also inhale air containing tobacco. This is called passive smoking .
Refer to text on page 141.

Question: Respiration can occur in two different manners. Briefly explain the process of aerobic respiration. How does it differ from anaerobic respiration?


Types of Respiration: On the basis of the presence or absence of oxygen, respiration is classified into two types:

1. Aerobic Respiration: When breakdown of glucose occurs with the use of oxygen, it is called aerobic respiration. During aerobic respiration, glucose is completely broken down into carbon dioxide and water and energy is released. Aerobic respiration takes place in mitochondria. It can be shown by the following equation:

Aerobic respiration is seen in most of the organisms such as humans (man), dogs, cats, lions, elephants, cows, buffaloes, goats, snakes, earthworms, frogs, fishes, etc.

2. Anaerobic Respiration: When breakdown of glucose takes place without using oxygen, it is called anaerobic respiration. The glucose is not completely broken down into carbon dioxide and water. An intermediate compound is formed with the release of less amount of energy during this process. It can be shown as follows:

Yeasts such as Saccharomyces cereviseae and certain bacteria carry out anaerobic respiration. These organisms that carry out respiration in the absence of oxygen are called anaerobes.

Question: Breathing rate of a person is not always constant. Give the reason for your answer.

Answer: The number of times a person breathes in a minute is termed as breathing rate. An adult human being can inhale and exhale 15-18 times in a minute. It is the average breathing rate of an adult human being.

Breathing rate of a person is not always constant. It changes according to the oxygen requirement of the body. Breathing rate is somewhat faster in women than in men and in children it is higher (20-30 times/min) than adults. Breathing rate is slowest while sleeping (as less energy is required) while maximum during heavy exercise like running, weight lifting, etc. (much energy is required). Increased breathing rate provides greater amount of air entry into the lungs, hence blood can absorb oxygen at a faster rate. Faster breathing supplies more oxygen to the body cell for producing more energy, required for heavy exercises.

During heavy exercise the breathing rate can increase upto 25 times per minute. Because of this, food gets broken down at a faster rate and thus make us feel hungry.

When we feel drowsy, sleepy or tired, we yawn (i.e. open our mouth wide to take a long and deep breathe, of air), because our breathing rate slows down and body do not receives sufficient oxygen.

Question: Whenever we feel drowsy or sleepy, we start yawning. Does yawning help us in anyway?

Answer: When we feel drowsy, sleepy or tired, we yawn (i.e. open our mouth wide to take a long and deep breathe, of air), because our breathing rate slows down and body do not receives sufficient oxygen.

Question: Respiration in fish is different from humans. Explain in brief how fishes can breathe through gills?

Answer: Fishes are the aquatic animals that live in water. These have a special organ for breathing called gills. The oxygen dissolved in water enters through the gills. Gills are actually the projections of skin and have blood vessels for the exchange of respiratory gases. The fishes breathes by taking in water through its mouth and sending it over the gills. The oxygen dissolved in the water is extracted by the gills and the extracted oxygen is absorbed by the blood.


This oxygen is then carried to all the parts of fishes for respiration. The carbon dioxide produced during respiration is brought back by the blood into the gills and expelled into the surrounding water.

Question: There are three animals named A, B and C. Among them A can stay on land as well as in water. When it stays at land is respire through lungs but when it goes into water, it respires through its moist skin. Animal B has specific organs to respire in the water which is not found in any other water animal. While animal C is a water animal which respires through nostrils and lungs. Now give the name of animal A, B and C.

Answer: Animal A can live on land as well as in water and can respire through lungs as well as moist skin. The animal is frog.

Animal B lives in water and respires through a specific organ called gills. These are found in the tadpoles besides fishes. The animal B is a fish.

Animal C is also an aquatic animal which lives in sea water and respires through nostrils and lungs not by the gills. The animal is whale.

Question: When breathe is released after holding it for few minutes. What happens and give reason for its occurrence?

Answer: Releasing breathe after holding it for sometime results in rapid breathing. It occurs to maintain a healthy balance between intake of O2 and release of carbon dioxide.

Question: Whales and dolphins are seen many times releasing a fountain of water sometimes at the surface of water. Why do they do so?

Answer: Sea animals like dolphins and whales live in water but unlike fishes, they do not possess gills for respiration. These possess nostrils which are called blow holes. There blow holes are located on the upper parts of their heads. These animals breathe in through their nostrils and lungs. Dolphins and whales comes to the surface of sea-water from time to time to breathe in air, sometimes whales release a function of water that moves upwards like a spray. This is because when a whale breathes air out of its blow hole it appears as a spray or misp, also called as spont. It can be seen from many miles away. Blow holes are surrounded by muscles that keep the holes closed when the whales or dolphins are under water and opens it when the animal is at the surface and needs to breathe.

Human cannot survive under water because they do not possess any gills to make use of oxygen dissolved in water for breathing. When we go under water we have to take oxygen gas cylinders for breathing.

Question: Observe the given diagram of human respiratory system. List the organs from (A) to (G).

Human respiratory system

Answer: The human respiratory system have following organs:

  1. Ribs
  2. Trachea
  3. Pharynx
  4. Diaphragm
  5. Lungs
  6. Nasal passage
  7. Oral cavity

Question: A girl was suffering from cold and was sneezing continuously. She joined her family at dinner and suddenly started sneezing without covering her nose, thus sending particles all over the place. On realizing her mistake, said sorry and next time covered her nose.

  1. During sneezing, what are the precautionary steps to be followed?
  2. Can infections be passed from one person to another via sneezing?
  3. Is sneezing a respiration process?
  4. What values do we pick from this situation?


  1. When sneezing, you should cover your nose so that the particles expelled by you would not be inhaled by others.
  2. Yes.
  3. No, it is process to remove / clear the particles harmful for us resulting in clean, fresh air to enter the lungs.
  4. Cleanliness and hygiene maintenance.

Question: 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 few hours, the dough had risen. There was a sour smell too.

  1. Why did the dough rise?
  2. Why did the dough smell sour?
  3. Why was sugar added to the dough?
  4. What would have happened if the dough was kept in the refrigerator, soon after it was prepared?


  1. The dough rises due to the release of carbon dioxide during anaerobic respiration by yeast cell.
  2. Yeast, during anaerobic respiration also produces alcohol which results in the sour smell of dough.
  3. Sugar is added into the dough, because it acts as a food for yeast. Yeast upon incomplete breakdown of sugar or food produces CO2, alcohol and energy (in less amount).
  4. If the dough is kept in the refrigerators after it was prepared, then dough will neither raise nor become sour. Yeast requires high temperature to grow, multiply and to respire. At low temperature, the yeast will not respire to produce the byproducts of anaerobic respiration.


  1. Plants lack a specialized respiratory system. How do they carry out respiratory process? Explain.
  2. The plant roots being underground respire by using which mechanism?


  1. The plants do not possess any respiratory system still plants respire. The various parts of the plants like leaves, roots, etc., carry out respiration independently.
    These parts take in oxygen from air in different manner and utilise it to obtain energy and give out C02. The leaves of plants possess tiny pores on their surface which is called as stomata. The gaseous exchange during respiration takes place through their stomata.
  2. Roots of the plants respire under the ground. Root cells get oxygen from the air present in the space between the soil particles.
    There are several root hairs present on the roots of a plant.
    The oxygen from the air (between soil particle) diffuses into root hair and reaches to the cells of the roots. This oxygen is utilized for respiration.

Question: 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.

  1. What can be the possible reasons for the pain in her legs?
  2. Why did she fell comfortable after a massage?


  1. Paheli had cramps in her leg muscles after running. She felt pain in her legs because of accumulation of lactic acid in the leg muscles. Lactic acid is formed due to anaerobic respiration in the muscle cells after heavy exercise or running. After heavy exercise, we require large amount of energy.
    To produce more energy to meet the oxygen requirement of muscles, muscle cells perform anaerobic respiration for a short duration.
    Lactic acid is formed due to partial breakup of glucose. It gets accumulated in the muscle cells and causes pain and muscle cramps.
  2. The massage or hot water bath gives the relief from muscle cramp or pain, because it improves the circulation of blood leading to increase supply of oxygen to the muscle cells. It helps in complete breakdown of lactic acid into carbon dioxide and water.

Question: It is not wise to sleep under a tree during night. Why?

Answer: During day, plants photosynthesis in the presence of sunlight and uses CO2 produced during respiration. During this process O2 is released as a byproduct and a balance between O2 and CO2 is maintained in the atmosphere.

But in the night, plants do not photosynthesis. Plants are unable to use CO2 during night and produces CO2 and takes O2 during respiration.

This leads to the increase in the proportion of CO2 in the air.

So, if one sleeps under a tree at night, he will have problems in breathing as the amount of CO2 in the air around will certainly be more than oxygen. Therefore, it is not advisable to sleep under trees during night because the person will suffer from suffocation and feel excess weight on chest.

Question: Observe the figures carefully and answer the following questions.

  1. Which process is being tested in the activity?
  2. What is the result of the activity? Give reasons.


  1. Exhalation process of respiration is being tested in the activity.
  2. The lime water in test tube B turns milky but water in test tube A remains unchanged. Because CO2 is present in the exhaled air, it mixes with lime water in test tube B and turns it milky.

Respiration in Organisms NCERT – Question:

  1. Respiratory process occurs in two phases, what are those two major steps of respiration? Describe each one.
  2. Define the term breathing rate.


  1. Respiration is the process of breakdown of food to produce energy for performing various functions. It involves two major steps:
    • Inhalation is the process of taking in of air which is rich in oxygen, inside our body.
    • Exhalation is the process of giving out of air which is rich in carbon dioxide from our body to the external environment.
  2. The number of times a person breathes, in a minute is called as breathing rate.
    An adult human being can inhale or exhale 15-18 times in a minute. It is the average breathing rate of an adult human being. Breathing rate is not constant always.

Respiration in Organisms NCERT – Question: Observe the given figures as A and B and answer the following questions.

  1. Among both figures identify which A or B indicates the process of inhalation and which shows the process of exhalation?
  2. In the figure label the arrows and indicate the direction of
  • movement of air
  • movement of diaphragm
  • movement of ribs


  1. Figure A indicates inhalation and figure B indicates exhalation.
  2. Movement of air, diaphragm and ribs are indicated in below figure:

Mechanism of breathing in human beings

Respiration in Organisms NCERT – Question: List some animals around you. Now group them as follows:

  1. Animals that can breathe only through skin.
  2. The animal that can breathe through skin as well as through lungs.
  3. The animal that can breathe through lungs.
  4. Animals that can breathe through gills.
  5. Animals that can breathe through spiracle and tracheae?


  1. Animals that can breathe only through skin are earthworm and leech.
  2. Animals that can breathe through skin as well as through lungs are frogs.
  3. Animals that can breathe through lungs are buffaloes, human, and dolphins.
  4. Animals that can breathe through gills are tadpole and fish.
  5. Animals that can breathe through spiracles and tracheae are grasshopper, cockroaches, ants, housefly and mosquito.

Question: Palak wants to be a great cyclist. She cycles daily for about 2 hours followed by some exercises. Today, she thought she will cycle for longer and managed it for 41/2 hours. Now she is feeling cramped up and her breathing is disturbed. Her mother took her to hospital where the doctor examined and told her not to push herself more than necessary. Palak understood and promised herself to move show and steadily.

  1. Why did Palak had cramps in her legs?
  2. Is breathing rate also affected after doing long hour of exercise. Why?
  3. When there is not enough oxygen supply,

what happens to body and process of respiration? What values you learn from this?


  1. Due to extensive exercise, formation of lactic acid occurred as muscles starts to respire anaerobically.
  2. Yes, breathing rate will be faster. Normally we are breathing at a slower rate but during physical activities, to make sufficient amount of O2 reaching cells we breathe faster.
  3. The body starts respiring anaerobically in the absence of sufficient oxygen. Glucose is partially broken into lactic acid which causes body cramps.
    Values learned – We should not force ourselves exercise but not over burn yourself discipline.

Question: A person put some warm water in an aquarium having fish during winter season. He thought that fish will be more comfortable in luke warm water than cold water. But he observed that fishes in the aquarium died. Why the fishes died in warm water?

Answer: The fishes have special type of organs for respiration called gills. These gills absorbs oxygen dissolved in water and through blood vessels, this oxygen is passed to all the parts of the body. The amount of dissolved oxygen is comparatively less in water than the amount of oxygen in air.

Therefore, the rate of breathing is also high in aquatic animals.

If we add warm water, to the aquarium the dissolved oxygen will dissociate and move into the atmosphere again, leaving the least percentage of oxygen into the water (as it is known that the solubility of gases in water goes down as the temperature rises). Therefore, fishes will have difficulty in breathing in the absence of oxygen and will die.

Question: A group of people were smoking cigarettes in a restaurant. The atmosphere was full of smoke. An old man sitting next to the group asked them to stop smoking while sitting in the premise or move out. They agreed to do so and promised not to repeat then mistake.

Answer the following questions.

  1. Write any three hazards of smoking.
  2. Can smoking also affect the person who does not smoke?
  3. Do you support the group’s decision to not smoke in public or individually. What values do we understand from here.


  1. Smoking is very injurious for the respiratory system. It harms lungs.
    • It causes blockage in respiratory tract.
    • It leads to lung cancer.
    • It can cause disease like asthma and heart diseases.
  2. Yes, smoking affects people who are passive smokers, i.e. those present nearby smokers.
  3. Yes, the people should bot smoke in public areas as it can cause discomfort to others.

The values we understand are obedience, respect elders and healthy habits.

Fill in the Blanks: Respiration in Organisms NCERT

  1. The roots of a plant take up oxygen from the ………….. trapped between the ………….. particles.
  2. Diaphragm forms the ………….. of the chest cavity.
  3. Exchange of gases in the leaves takes place with the help of …………..
  4. Cockroaches breathe with the help of air tubes called …………..
  5. ………….. is an essential phenomenon for the survival of living organisms.
  6. During aerobic respiration the food is broken down into ………….. and ………….. and releases a lot of …………..
  7. Taking in of air rich in O2 inside the body is called …………..
  8. Breathing rate of a person is not ………….. always …………..
  9. Unwanted particles like smoke, dust, pollen, etc., are called …………..
  10. Lungs are very ………….. organ.


  1. air, soil
  2. floor
  3. stomata
  4. tracheae
  5. Breathing
  6. carbon dioxide, water, energy
  7. inhalation
  8. constant
  9. allergen
  10. delicate

True / False

  1. Oxygen breaks down glucose outside the cells of organisms.
  2. Frogs can breathe through their skin as well as lungs.
  3. Insects have spiracles on the lower surface of the body.
  4. Exhaled air has more percentage of CO2 than inhaled air.
  5. Living organism respire to get energy from food.
  6. Plants respire through leaves and roots.
  7. Cell is the smallest structural and functional unit of the body.
  8. We take deep breathes after we hold on breath for the one minute.
  9. The exchange of gases in plants takes place through stomata.
  10. The balance between CO2 and O2 is maintained by the plants.


  1. 1. False, oxygen breaks down glucose inside the cells of organisms.
    2. True
    3. False, insects have spiracles on the sides of the body.
    4. True
    5. True
    6. True
    7. True
    8. True
    9. True
    10. True

Question: Match the names of organisms in Column I with their organs of breathing given in Column II.

Column I Column II
(a) Butterfly (i) Lungs
(b) Earthworm (ii) Gills
(c) Sparrow (iii) Spiracles
(d) Fish (iv) Skin


  1. (a)-(iii)
  2. (b)-(iv)
  3. (c)-(i)
  4. (d)-(ii)

Respiration in Organisms NCERT – Question: Match the items in Column I with those in Column II.

Column I Column II
(a) Plant (i) Earthworm
(b) Cell (ii) Stomata
(c) Frog (iii) Single celled
(d) Lungs (iv) Lungs
(e) Skin (v) Spiracles
(f) Yeast (vi) Oxygen
(g) Mammals (vii) Structural and functional unit of body
(h) Leaves (viii) Chest cavity
(i) Inhalation (ix) Lungs and moist skin
(j) Cockroaches (x) Stomata, lenticels and roots


  1. (a)-(x)
  2. (b)-(vii)
  3. (c)-(ix)
  4. (d)-(viii)
  5. (e)-(i)
  6. (f)-(iii)
  7. (g)-(iv)
  8. (h)-(ii)
  9. (i)-(vi)
  10. (j)-(v)

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