NCERT Class 7 Science Chapter 6 Respiration in Organisms: Notes and Solutions (Free PDF)

NCERT Class 7 Science Chapter 6 on Respiration in Organisms is an extension of some concepts in CBSE Class 6 Science Chapter 4: Getting to know Plants and Chapter 6: The Living Organisms- Characteristics and Habitats. Also, this chapter should be read in continuity with Class 7 Science Chapters 2 and 3. When you start browsing through the notes, you will learn about respiration and breathing in human beings, cockroaches, earthworms, and plants. In addition, our subject experts have also provided answers to writing questions following this chapter. Let’s start!!

Download NCERT Science Class 7 Science Chapter 6 Important Questions and Answers PDF

Explore all the Chapters of Class 7 Science: 

Chapter 1	Chapter 2	Chapter 3	Chapter 4	Chapter 5	Chapter 6
Chapter 7	Chapter 8	Chapter 9	Chapter 10	Chapter 11	Chapter 12
Chapter 13

Revise CBSE Notes Class 6 Science

Respiration

Before we start learning about Respiration as mentioned in the NCERT Class 7 Science Chapter 6 Respiration in Organisms, let us revise what we have learnt in Class 7 Science Chapter 2. In Chapter 2 we got to know that the cell is the smallest and most fundamental unit of a living organism. Also, cells assist in bodily functions such as nutrition, excretion, and reproduction. To carry out these functions, the cells require energy. The energy is derived from the food we intake as food has stored energy that is released during respiration. 

In respiration, we breathe the air around us. We inhale oxygen and exhale carbon dioxide. The air we inhale is carried throughout the entire body, reaching each individual cell. Within these cells, the oxygen from the air plays a crucial role in the process of breaking down food.

Cellular Respiration

The breakdown of food or glucose within cells releases energy. The food in the cell is broken down into water (H20) and carbon dioxide (CO2) in the presence of oxygen. This process is known as “cellular respiration”. It is a universal process occurring in the cells of all living organisms.

Aerobic and Anaerobic Respiration 

Now that we are familiar with cellular respiration, let us understand aerobic and anaerobic respiration.

Aerobic Respiration	Anaerobic Respiration
In aerobic respiration, glucose breaks down in cells with the help of oxygen.	In anaerobic respiration, glucose breaks down in cells without oxygen.
Glucose———–> CO2+H20+Energy (In the presence of oxygen)	Glucose————>Alcohol+CO2+Energy (In the absence of oxygen)
Organisms that perform aerobic respiration: Human beings, Cows, Buffaloes	Organisms that perform anaerobic respiration (aka Anaerobes): Yeast

Anaerobic Respiration in Human Beings:  Human muscle cells are capable of undergoing anaerobic respiration, but this can only occur briefly when there is a temporary shortage of oxygen. In situations such as intense exercise, like fast running, cycling, prolonged walking, or heavy weightlifting, the body’s energy demand is substantial. However, the available oxygen supply to generate this energy is restricted. In such cases, muscle cells resort to anaerobic respiration to meet the energy demand. Here is how human muscles gain energy through anaerobic respiration: Glucose———————————————> Lactic Acid+Energy (In the absence of oxygen) (in human muscles) Production of Lactic Acid due to partial breakdown of glucose results in muscle cramps caused during exercise or other physical activity. To get relief from cramps, it is advisable to take a massage or a hot water bath. Both hot water baths and massage improve blood circulation due to which the supply of oxygen increases in our muscles. Further, oxygen supply breaks down the glucose completely and converts lactic acid to CO2 and H2O. This in turn reduces cramp pains as well.

Also Read: Human Muscular System: Parts, Function, Organs, Facts

Breathing in Human Beings

The process of taking in air with high oxygen volume and giving out air with high CO2 content through the respiratory organs is known as breathing. Let us now dive into different concepts of breathing in human beings as mentioned in the NCERT Class 7 Science Chapter 6. 

Inhalation and Exhalation

• Inhalation: The process of taking in air rich in oxygen into the body is referred to as “inhalation”. 
• Exhalation: On the other hand, the act of giving out air rich in carbon dioxide from the body is known as “exhalation”.

Breathing Rate

The frequency at which an individual takes breaths within a minute is referred to as the “breathing rate”. Breathing involves the alternating processes of inhalation and exhalation. A single breath comprises one inhalation followed by one exhalation.

An adult human being has a breathing rate of 15 to 18, usually. However, during physical exercises, the rate can increase up to 25.

Mechanism of Breathing

Let us now walk through the respiratory system of the human body to understand the mechanism of breathing.

Respiratory System

• Nostrils: We inhale air through our nose via the two holes known as “nostrils”.
• Nasal Cavity: From the nostrils, the air is transferred to the respiratory system via the “nasal cavity”.
• Lungs: The nasal cavity transfers inhaled air to the pair of spongy, pinkish-grey organs known as the “lungs”. Both lungs are present in our “chest cavity”.
• Chest Cavity: The space in our chest that holds our lungs, heart, tissues, etc is known as “chest cavity”. This cavity is surrounded by ribs to protect our internal organs.
• Diaphragm: The muscular floor of the chest cavity is known as the “diaphragm”. 

Mechanism of Breathing

Now, let us understand the mechanism:

The process of breathing is facilitated by the coordinated movement of the diaphragm and the rib cage. When we inhale, the ribs expand upward and outward, while the diaphragm moves downward. These actions create more space in our chest cavity, allowing air to flow into the lungs, thereby filling them with air. 

Whereas, during exhalation, the ribs move downward and inward, and the diaphragm returns to its initial position by moving upward. This contraction of the chest cavity reduces its size, pushing air out of the lungs.

Also Read: Human Body Systems and Functions

Breathing in Other Animals

Furthermore, in NCERT Class 7 Science Chapter 6, we also learn about respiration in other living organisms like cockroaches and earthworms.

Cockroach

Cockroaches have small openings on their body. These openings are known as “spiracles”. 

Also, they have a network of air tubes known as “trachea”, which is used for the exchange of gases. In a cockroach, oxygen-laden air enters its body through spiracles. Thereafter, air from spiracles gushes into tracheal tubes. Now, the air diffuses into the body tissue of the cockroach and reaches each cell of this insect. 

Likewise, carbon dioxide-rich air from the cells travels to tracheal tubes. From there, the exhaled air moves out into the atmosphere through the spiracles. 

Earthworm

Earthworms breathe through their skin. These organisms inhale and exhale air via their warm and slimy skin. 

Check out: Breathing And Exchange of Gases – Class 11

Breathing under Water

Now, let us explore how fishes breathe underwater.

Fish utilize their gills to extract oxygen that is dissolved in water. Gills are extensions of the fish’s skin. Gills are equipped with an extensive network of blood vessels that facilitate the exchange of gases. This allows fish to extract oxygen from the water and release carbon dioxide. 

Breathing in Plants

Besides, NCERT Class 7 Science Chapter 6 on Respiration in Organisms also enables us to understand respiration in plants. 

Plants, like all other living organisms, engage in respiration to ensure their survival. They, too, absorb oxygen from the air and release carbon dioxide. Inside plant cells, oxygen is used to break down glucose into carbon dioxide and water, similar to the process in other organisms. 

Different parts of plants can individually take in oxygen from the air and release carbon dioxide. In plants, leaves possess small openings known as stomata, which are used for the exchange of oxygen and carbon dioxide. 

Also, just like all other living cells within plants, the cells in plant roots require oxygen to produce energy. Roots obtain air by absorbing it from the spaces found between the soil particles.

Also Read: Respiration in Plants

Explore all the Chapters of Class 7 Science: 

Chapter 1	Chapter 2	Chapter 3	Chapter 4	Chapter 5	Chapter 6
Chapter 7	Chapter 8	Chapter 9	Chapter 10	Chapter 11	Chapter 12
Chapter 13

NCERT Solutions Class 7 Science Chapter 6: Respiration in Organisms

Ques 1. Why does an athlete breathe faster and deeper than usual after finishing the race?

Ans: Athletes require a significant amount of energy during a race, and in order to access this energy, they must increase their breathing rate to get the necessary oxygen. This is why they breathe more rapidly than usual after completing a race.

Ques 2. List the similarities and differences between aerobic and anaerobic respiration.

Ans: Here are the differences between aerobic and anaerobic respiration:

Aerobic Respiration	Anaerobic Respiration
In aerobic respiration, glucose breaks down in cells with the help of oxygen.	In anaerobic respiration, glucose breaks down in cells without oxygen.
Glucose———–> CO2+H20+Energy (In the presence of oxygen)	Glucose————>Alcohol+CO2+Energy (In the absence of oxygen)

Ques 3. Why do we often sneeze when we inhale a lot of dust-laden air?

Ans: Inhaling air that contains dust particles can lead to irritation in the nose, prompting a reflexive response that results in sneezing to expel the dust.

Ques 5. Select the correct answer:

a. In cockroaches, air enters the body through

(i) Lungs

(ii) Gills

(iii) Spiracles

(iv) Skin

b. During heavy exercise, we get cramps in the legs due to the accumulation of

(i) Carbon dioxide

(ii) Lactic acid

(iv) Alcohol

(v) Water

c. Normal range of breathing rate per minute in an average adult person at rest is:

(i) 9 to 12

(ii) 15 to 18

(iii) 21 to 24

(iv) 30 to 33

d. During exhalation, the ribs

(i) Move outwards

(ii) Move downwards

(iii) Move upwards

(iv) Do not move at all

Ans:

a. Option (ii) Spiracles

b. Option (ii) Lactic Acid

c. Option (ii) 15 to 18

d. Option (iii) Move upwards

Ques 6. Match the items in Column I with those in Column II.

Column I	Column II
a. Yeast	(i) Earthworm
b. Diaphragm	(ii) Gills
c. Skin	(iii) Alcohol
d. Leaves	(iv) Chest cavity
e. Fish	(v) Stomata
f. Frog	(vi) Lungs and skin
	(vii) Trachae

Ans:

Column I	Column II
a. Yeast	(iii) Alcohol
b. Diaphragm	(iv) Chest cavity
c. Skin	(i) Earthworm
d. Leaves	(v) Stomata
e. Fish	(ii) Gills
f. Frog	(i) Earthworm

Ques 7. Which of the following statements are True or False:

a. During heavy exercise the breathing rate of a person slows down.

b. Plants carry out photosynthesis only during the day and respiration only at night.

c. Frogs breathe through their skins as well as their lungs.

d. The fishes have lungs for respiration.

e. The size of the chest cavity increases during inhalation.

Ans:

a. False

b. False

c. True

d. True

Ques 8. Given below is a square of letters in which are hidden different words related to respiration in organisms. These words may be present in any direction — upwards, downwards, or along the diagonals. Find the words for your respiratory system. Clues about those words are given below the square.

S	V	M	P	L	U	N	G	S
C	Z	G	Q	W	X	N	T	L
R	M	A	T	I	D	O	T	C
I	Y	R	X	Y	M	S	R	A
B	R	H	I	A	N	T	A	Y
S	T	P	T	B	Z	R	C	E
M	I	A	M	T	S	I	H	A
S	P	I	R	A	C	L	E	S
N	E	D	K	J	N	S	A	T

(i) The air tubes of insects

(ii) Skeletal structures surrounding the chest cavity

(iii) Muscular floor of chest cavity

(iv) Tiny pores on the surface of a leaf

(v) Small openings on the sides of the body of an insect

(vi) The respiratory organs of human beings

(vii) The openings through which we inhale

(viii) An anaerobic organism

(ix) An organism with a tracheal system

Ans:

(i) Trachea

(ii) Ribs

(iii) Diaphragm

(iv) Stomata

(v) Spiracles

(vi) Lungs

(vii) Nostrils

(viii) Yeast

(ix) Ant

S	V	M	P	(vi) L	U	N	G	S
C	Z	G	Q	W	X	(vii) N	(i) T	L
(ii) R	M	A	T	I	D	O	T	C
I	Y	R	X	Y	M	S	R	A
B	R	H	I	(ix) A	N	T	A	(viii) Y
S	T	P	T	B	Z	R	C	E
M	I	A	M	T	S	I	H	A
(iv S	P	I	R	A	C	L	E	S
N	E	(iii) D	K	J	N	S	A	T

Ques 9. The mountaineers carry oxygen with them because:

a. At an altitude of more than 5 km, there is no air.

b. The amount of air available to a person is less than that available on the ground.

c. The temperature of the air is higher than that of the ground.

d. The pressure of air is higher than that on the ground.

Ans: Option b. The amount of air available to a person is less than that available on the ground.

FAQs

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