NCERT Exemplar Solutions Class 7 Science Respiration in Organisms

Multiple Choice Questions

Question 1:   Sometimes when we do heavy exercise, anaerobic respiration takes place in our muscle cells. What is produced during this process?

(a) alcohol and lactic acid

(b) alcohol and CO₂

(c) lactic acid and CO₂

(d) lactic acid only 

Solution 1:  (d) lactic acid only

Oxygen is used up more rapidly during exercise, so our body switches to anaerobic respiration to fulfil the oxygen demand because of which lactic acid is formed instead of pyruvic acid.

Question 2:  Yeast is used in the wine and beer industries because it respires

(a) aerobically producing oxygen.

(b) aerobically producing alcohol.

(c) anaerobically producing alcohol.

(d) anaerobically producing CO₂. 

Solution 2:  (c) anaerobically producing alcohol.

To generate ethanol and CO₂, yeast breathes anaerobically because of this characteristic; it is used in the manufacture of ethanol and alcoholic beverages.

Question 3:  During the process of exhalation, the ribs move

(a) down and inwards.

(b) up and inwards.

(c) down and outwards.

(d) up and outward. 

Solution 3:  (a) down and inwards.

The diaphragm goes up during exhalation and the ribs move backward and upward, reducing the gap in the chest cavity, raising the weight of the breath within the lungs and pushing the air out of the lungs.

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?

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (i) and (iii)

(d) (ii) and (iv) 

Solution 4:  (c) (i) and (iii)

Breathing is a mechanism in which oxygen-free air is drawn into the lungs and, with the aid of respiratory organs, carbon-di-oxide rich air is expelled from the body.

Question 5:  Fish breathe with the help of gills which are richly supplied with blood vessels. The gills help the fish to

(a) take in oxygen from the air.

(b) take in oxygen dissolved in water.

(c) absorb nutrients present in water.

(d) release waste substances in water. 

Solution 5:  (b) take in oxygen dissolved in water.

For the exchange of fluids, fishes use gills. It runs through the gills as the water reaches through the mouth. In the gills, capillaries absorb oxygen trapped in water and tend to remove CO2 from the body as well.

Question 6:  Earthworms and frogs breathe through their skin because of which the skin of both the organisms is

(a) moist and rough.

(b) dry and rough.

(c) dry and slimy.

(d) moist and slimy. 

Solution 6:  (d) moist and slimy. 

In earthworms and frogs, gas exchange takes place through diffusion across the wet body, so their skin looks 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.

(b) Frogs can breathe through their skin as well as lungs.

(c) Insects have spiracles on the lower surface of the body.

(d) Exhaled air has more percentage of CO₂ than inhaled air. 

Solution 7: 

a) False- Within the cells of animals, oxygen breaks down glucose.

b) True

c) False- Insects are on the sides of the body like spiracles.

d) True

Question 8:  Fill in the blanks with suitable words.

(a) The roots of a plant take up oxygen from the ______ trapped between the ________ particles.

(b) Diaphragm forms the ___________ of the chest cavity.

(c) Exchange of gases in the leaves takes place with the help of __________.

(d) Cockroaches breathe with the help of air tubes called ___________. 

Solution 8:

(a) The roots of a plant take up oxygen from the air trapped between the soil particles.

(b) The diaphragm forms the floor of the chest cavity.

(c) Exchange of gases in the leaves takes place with the help of stomata.

(d) Cockroaches breathe with the help of air tubes called tracheae.

Short Answer Questions.....................

Question 9:  Pick the odd-one-out from each of the groups given below on the basis of respiratory organs. Give a reason for your answer.

(a) cockroach, grasshopper, snail, ant

(b) lizard, cow, earthworm, snake

(c) crocodile, whale, dolphin, fish

(d) snake, tadpole, crow, goat 

Solution 9:

a) Snail

Cockroach, grasshopper and ants breathe by the trachea but snail does not breathe by trachea.

b) Earthworm

Lizard, cow and snake breathe through their lungs while earthworm breathes through its skin as it does not have lungs.

c) Fish

Fishes breathe by their gills as they don’t have lungs.

d) Tadpoles

Since tadpoles have no lungs so they breathe by their gills.

Question 10:  Which gas present in the air is essential for aerobic respiration? What is the role of oxygen during respiration? 

Solution 10:   For the aerobic respiration process, atmospheric oxygen is essential. Respiration is vital because food is broken down by oxygen and releases steam.

Question 11:  On 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.

Solution 11:  Sleeping > watching T.V. > brisk walk > cycling

Breathing becomes quicker when a person does a physical exercise. The cells need more fuel to provide more energy because of this. 

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. 

Solution 12:   If the atmosphere is cool, the warm and humid air we exhale condenses into mist when it comes into contact with the cold ambient air. It looks like smoke is coming out of your mouth.

Question 13:  Whenever we feel drowsy or sleepy, we start yawning. Does yawning help us in any way? 

Solution 13:     

The sleepy rate of respiration slows down as we sense it. Because of this, we don't get enough air from our lungs and we yawn. Yawning fills the lungs with additional oxygen which allows them to stay alive.

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? 

Solution 14:

(i) On the sides of the insect's body, spiracles are present, while stomata are present on the lower surface of the stems.

(ii) Spiracles are less in number if compared to stomata.

(iii) Spiracles add to a large network of a tracheal structure that is absent from the 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?

(b) Why did she feel comfortable after a massage? 

Solution 15:

a) The build-up of lactic acid in her tissues may be due to pain in her thighs. Cells breathe anaerobically, releasing lactic acid during vigorous physical exercise.

b) As it raises blood pressure, the massage gave her relief, leading to increased oxygen supply to the muscle cells, which helps to incompletely break down lactic acid into CO₂ and water.

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?

(b) In which jar, will the amount of CO₂ be the lowest and why? 

Solution 16:

a) The volume of CO₂ in jar C will be the largest so mice will breathe out CO₂ in jar C, resulting in CO₂ accumulation in jar C.

b) The volume of CO₂ in jar A will be the lowest so plants will use CO₂ in jar A for breathing.

Question 17:  Observe Figure 10.2 carefully and answer the following questions.

(a) Which process is being tested in the activity?

(b) What is the result of the activity? Give reasons. 

Solution 17:

a) This procedure is used to test the mechanism of exhalation during respiration.

b) In test tube B, lime water becomes milky and test tube A stays unchanged when CO₂ blends with lime water in 'B' in the exhaled air and makes it milky.

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

(a) Why did the dough rise?

(b) Why did the dough smell sour?

(c) Why was sugar added to the dough?

(d) What would have happened if the dough was kept in the refrigerator, soon after it was prepared? 

Solution 18:

a) The CO₂ produced by yeast during respiration lifts the dough.

b) Alcohol is produced during anaerobic respiration by yeast. This gives the dough a sour smell.

c) Sugar behaves as food for yeast.

d) Yeast cannot breathe and replicate while held in the oven, and the dough does not rise and does not create a bad scent.

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 the process of exhalation?

(b) In the figure label the arrows and indicate the direction of

(i) movement of air

(ii) movement of diaphragm

(iii) movement of ribs 

Solution 19:

a) Figure (A) indicates the process of inhalation.

     Figure (B) indicates the process of exhalation.

Question 20:  Match the names of organisms in Column I with their organs of breathing given in Column II.

Solution 20: