NCERT Exemplar Problems Class 7 Science – Respiration in Organisms

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 C0₂
(c) Lactic acid and C0₂
(d) Lactic acid only
Answer:
(d) During heavy exercise, anaerobic respiration takes place in our muscle cells. This happens as the oxygen gets used up faster in our muscle cells than can be supplied by the blood.
To produce extra energy for exercise, the muscle cells shift to anaerobic respiration.

Question 2:
Yeast is used in wine and beer industries because it respires
(a) aerobically producing oxygen
(b) aerobically producing alcohol
(c) anaerobically producing alcohol
(d) anaerobically producing CO2
Answer:
(c) Yeast is used in wine and beer industries because it respires
(a) aerobically producing oxygen (b) aerobically producing alcohol (c) anaerobically producing alcohol (d) anaerobically producing CO2

The alcohol is used in wine and beer industry, while the CO₂ is used in bread making.

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 outwards
Answer:
(a) During exhalation, ribs move down and inwards, while diaphragm move upwards and relaxes. This reduces the size of the chest cavity and air is pushed out of the lungs.

Question 4:
Breathing is a process that
(a) provides 0₂ to the body
(b) breaks down food to release energy
(c) helps the body to get rid of C0₂
(d) produces water in the cells
Answer:
(c) Breathing is a process by which air rich in oxygen is taken inside the body and air rich in carbon dioxide is expelled from the body, with the help of respiratory organs.
It is a continuous process which goes on all the time and throughout the life of an organism.

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 air
(b) take in oxygen dissolved in water
(c) absorb nutrients present in water
(d) release waste substances in water
Answer:
(b) Fish has special organs called gills that help it to use oxygen dissolved in water. Gills are projections of the skin that are well supplied with blood vessels for exchange of gases.

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
Answer:
(d) Earthworms and frogs have moist and slimy skin that helps them to absorb the oxygen for respiration.

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 C0₂ than inhaled air.
Answer:
(a) False, Oxygen breaks down glucose inside the cells of organisms.
(b) True
(c) False, Insects have spiracles on the sides of the body.
(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…………………
Answer:
(a) air; soil
(b) floor
(c) stomata
(d) tracheae

Short Answer Type 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
(b) Lizard, cow, earthworm, snake
(c) Crocodile, whale, dolphin, fish
(d) Snake, tadpole, crow, goat
Answer:
(a) Snail is the odd one, as it does not breathe by means of tracheae.
(b) Earthworm is the odd one, because it breathes through its skin and it does not have lungs.
(c) Fish is the odd one, as most fish breathe through their gills and do not have lungs.
(d) Tadpole is the odd one, as it breathes through gills and do not have lungs.

Question 10:
Which gas present in air is essential for aerobic respiration? What is the role of this gas during respiration?
Answer:
Oxygen gas present in air is essential for aerobic respiration. It breaks down food and releases energy during respiration.

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 reason for your answer.
Sleeping, cycling, brisk walk, watching TV.
Answer:
In order of increasing breathing rates, the activities are:
Sleeping < Watching TV < Brisk walk < Cycling
This is because whenever, a person does an activity, the breathing rate increases depending on the nature of the activity. With strenuous work to provide more oxygen to cells for more energy, the breathing rate further increases.
Therefore, sleeping has minimum breathing rate, while cycling (a physical exercise) has maximum rate.

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

Question 13:
Whenever we feel drowsy or sleepy, we start yawning. Does yawning help us in anyway?
Answer:
Yawning is the action of opening one’s mouth wide while taking a long and deep breath of air. It is caused by insufficient oxygen in the body.
It usually occurs when we are drowsy or sleepy because our breathing rate slows down during these situation. The lungs do not get enough oxygen from the air for respiration. Yawning helps in bringing more oxygen into the body through the wide open mouth.

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?
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:
(i) Spiracles are fewer in number as compared to stomata.
(ii)Spiracles lead to an extensive network of tracheal system, which is absent in the leaves.
(iii)Spiracles are present on the sides of insect’s body while stomata are present on the surface of leaves.

Long Answer Type Questions

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 situation.
(a) What can be the possible reasons for the pain in her legs?
(b) Why did she fell comfortable after a massage?
Answer:
(a) 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 the anaerobic respiration in the muscle cells after heavy exercise or running.
During heavy exercise, we require large amount of energy that is provided by muscle cells through anaerobic respiration (Oxygen present is used up for energy, so there is lack of oxygen).
Due to the partial breakup of glucose lactic acid is formed. It gets accumulated in the muscle cells and causes pain and muscle cramps.
(b) The massage or hot water bath gives relief from muscle cramps or pain, because it improves the circulation of blood leading to increased supply of oxygen to the muscle cells. It helps in complete breakdown of lactic acid into carbon dioxide and water.

Question 16:
Observe the given figures carefully and answer the following questions.
(a) The amount of C0₂ be the highest in which jar. Why?
(b)The amount of C0₂ be the lowest in which one and why?

Answer:
(a) The amount of C0₂ will be the highest in jar C. It is because the mice kept under the jar will breathe out C0₂ continuously increasing its amount in the jar.
In other jars, the C0₂ present inside will be used up by the plants for photosynthesis.
So, its So, amount will decrease.
(b) The amount of CO2 will be the lowest in jar A. It is because in jar A, C0₂ released during respiration is used by the plant for the process of photosynthesis.
In jar B, the C0₂ is continuously released by the rats. So, its amount will remain same. In jar C, C0₂ released by rats is not used up at all as there is no plant.

Question 17:
Observe the figure 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.
Answer:
(a) Exhalation, a part of process of respiration is being tested in the activity.
(b) The lime water in test tube 6 turns milky, but water in test tube A remains unchanged. Because C0₂ present in the exhaled air, mixes with lime water in test tube B and turns 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?
Answer:
(a) The dough rose due to the release of carbon dioxide during anaerobic respiration by the yeast.
(b) Yeast, during anaerobic respiration also produces alcohol which results in the sour smell of dough.
(c) Sugar is added into the dough, because it acts as a food for yeast. Yeast on incomplete breakdown of sugar or food produces C0₂, alcohol and energy (in less amount).
(d) If the dough was kept in the refrigerator soon after it was prepared, then dough will neither rise nor become sour. Yeast requires high temperature to grow, multiply and to respire. At low temperature, the yeast will not multiply or respire and therefore, no C0₂ or alcohol would be formed.

Question 19:
Observe the given figures labelled as A and B and answer the following questions.
(b) Movement of air, diaphragm and ribs are indicated in below figures:

(a) Which of the figures, A or B indicates the process of inhalation and which shows 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.
Answer:
(a) Figure A indicates inhalation and figure 6 indicates exhalation. During inhalation, the ribs contract to move outward and upward, while during exhalation, the movement reverses, i.e. ribs relaxes to move inward and downward.

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

Answer:
The correct matching is as given:
(a)—(iii), (b)—(iv), (c)—(i), (d)—(ii)
(a)Butterfly is an insect, that has openings called spiracles on the sides of its body for taking in oxygen rich air.
(b)Earthworm breathes through its most and slimy skin.
(c) Sparrow (i.e. bird) has lungs and numerous air sacs for circulation of air.
(d)Fish has gills that are well supplied with blood vessels to use oxygen dissolved in water.