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Page No 137:

Question 1:

1. Before the air enters the trachea, it must pass through the _________________
(a) alveoli
(b) bronchi
(c) pharynx
(d) bronchioles


(c) pharynx

Pharynx is also called the throat. It is a common passage for food and air. Inhaled air passes from the nasal cavities to the trachea through the pharynx. 

Page No 137:

Question 2:

The place where exchange of gases takes place is the __________________.
(a) larynx
(b) alveoli
(c) trachea
(d) bronchi


(b) alveoli

Alveoli are balloon-like air pockets present in the lungs. These are also called miniature lungs. The exchange of gases takes place in the alveoli.

Page No 137:

Question 3:

In insects the exchange of gases takes place through _______________.
(a) spiracles
(b) gills
(c) lungs
(d) lenticels


(a) spiracles

Insects breathe through the holes on their bodies; these holes are called spiracles. Thus, the exchange of gases in insects takes place through the spiracles.

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Question 4:

The exchange of gases in roots take place through ________________.
(a) stomata
(b) gills
(c) general surface
(d) spiracles


(c) general surface

In plants, the exchange of gases in roots takes place through the general surface. 

Page No 137:

Question 5:

When do plants respire?
(a) only at night
(b) only during day time
(c) only at sunset and sunrise
(d) throughout the day and the night


(d) Throughout the day and night

Respiration in plants takes place during the day and night.

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Question 6:

Amoeba breathes through its ________________.
(a) lungs
(b) general surface
(c) alveoli
(d) vacuoles


(b) general surface

Amoeba does not have respiratory organs; oxygen and carbon dioxide diffuse in and out through the outer cell membrane or general surface.

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Question 7:

Tadpoles breathe through _______________.
(a) lungs
(b) skin
(c) gills
(d) both lungs and gills


(a) gills

Tadpoles breathe through gills. As tadpoles mature into frogs, they develop lungs. Frogs breathe through their lungs and moist skin.

Page No 137:

Question 8:

Which of the following do not carry out aerobic respiration?
(a) humans
(b) yeast
(c) dogs
(d) peepal tree


(b) Yeast

Yeasts do not carry out aerobic respiration. They respire anaerobically. Humans, dogs and peepal tree respire aerobically.

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Question 9:

Adult frogs have
A. lungs
B. gills
C. lenticels
D. spiracles

(a) only B is correct
(b) both B and D are correct
(c) only A is correct
(d) B, C, and D are correct


(c) Only A is correct.

Adult frogs respire through the lungs and the skin.

Page No 137:

Question 10:

Mark the following statements as true (T) or false(F). Rewrite the incorrect statements correctly.
(a) Insects breathe through gills.
(b) Bronchioles are wider than bronchi.
(c) Exhaled air has more dust than inhaled air.
(d) Alveoli are thin walled sacs.
(e) Anaerobic respiration requires oxygen.
(f) Earthworms take in oxygen through their moist skin.
(g) Plants do not have a respiratory system.
(h) Carbon dioxide and water are the two products given out during respiration.
(i) You can stop your breathing for hours at a time.
(j) The hairy and sticky lining in your nose filters out dust and germs.
(k) Yeasts respire aerobically.
(l) Plants respire only during daytime.
(m) Adult frogs respire through gills and lungs.
(n) Exhaled air is rich in carbon dioxide and dust particles.


(a) False
Insects respire through spiracles.

(b) False
Bronchioles are narrower than bronchi.

(c) False
Exhaled air has less dust than inhaled air.

(d) True

(e) False
Anaerobic respiration does not require oxygen.

(f) True

(g) True

(h) True

(i) False
You can stop breathing for a very short time.

(j) True

(k) False
Yeasts respire anaerobically.

(l) False
Plants respire throughout the day.

(m) False
Adult frogs respire through the skin and lungs.

(n) False
Exhaled air is rich in carbon dioxide, but it does not contain dust particles.

Page No 138:

Question 11:

Differentiate between the following pairs of words.
(a) respiration and burning
(b) breathing and respiration
(c) aerobic and anaerobic respiration



Respiration Burning
Respiration is a slow process. Burning is a fast process.
Energy released can be stored and used later. Energy is released in the form of heat and light and thus cannot be stored.
Respiration involves the use of certain enzymes for the oxidation of food. No enzymes are required in the process of burning.

Breathing  Respiration
Breathing is a mechanical process. Respiration is a chemical process.
Breathing does not result in the release of energy. Energy is released during respiration.

Aerobic Respiration Anaerobic Respiration
It takes place in the presence of oxygen. It takes place in the absence of oxygen.
Humans respire aerobically. Yeasts respire anaerobically.

Page No 138:

Question 12:

Define the following terms.
breathing, cellular respiration, anaerobic respiration


Breathing is taking in oxygen and giving out carbon dioxide.

Cellular respiration involves release of energy by the oxidation of food and conversion of the released energy into a biologically usable form.

Anaerobic respiration is the respiration that takes place in the absence of oxygen.

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Question 13:

Give four differences between photosynthesis and respiration.


Photosynthesis Respiration
In photosynthesis, carbon dioxide and water combine to form glucose in the presence of sunlight. In respiration, glucose is broken down into carbon dioxide and water with the help of respiratory enzymes.
It occurs in green plants only. In occurs in all organisms.
In photosynthesis, energy is consumed. In respiration, energy is released.
It takes place during the daytime. It takes place throughout the day.

Page No 138:

Question 14:

Explain how the diaphragm and ribs help in the process of breathing.


During inhalation, the diaphragm moves downwards and the ribs move upwards and outwards, thereby increasing the space in the chest cavity. This leads to the movement of air inside the lungs.

During exhalation, the diaphragm moves to its former position and the ribs move downwards and inwards, thereby reducing the size of the chest cavity. This leads to the movement of air out of the lungs.

Page No 138:

Question 15:

What is the importance of respiration in living organisms?


Respiration is the process in which energy is released. This energy can be stored and used later for various vital processes in living organisms. 

Page No 138:

Question 16:

Label the different parts of the respiratory system shown by arrows in the diagram.


(a) Nasal passage
(b) Pharynx
(c) Lungs
(d) Ribs
(e) Diaphragm

Page No 138:

Question 17:

(a) What is given out during respiration is used up during photosynthesis. Explain this statement.
(b) Complete the following word equation.
food(glucose) + oxygen ⟶ _______________ + ________________ + __________________


(a) During respiration, glucose is oxidised to give carbon dioxide and water along with energy.

Equation for respiration:
C6H12O6 +6O26CO2 + 6H2O+Energy

Photosynthesis is the process in which green plants synthesise their food (glucose) with the help of sunlight. In this process, carbon dioxide combines with water to form glucose.

Equation for photosynthesis:
6CO2 + 6H2O+Energy C6H12O6+6O2 

Hence, what is given out in respiration is used in photosynthesis.

(b) Food (Glucose)+OxygenCarbon dioxide+Water+Energy

Page No 138:

Question 18:

List the parts of the body in the order in which air flows through them starting from nostrils and ending with the alveoli.


Nostrils  Pharynx  Trachea  Larynx  Bronchi  Bronchioles  Alveoli

Page No 138:

Question 19:

What happens during swallowing? How is air kept separate from food in the digestive system?


Swallowing is the process in which food passes from the mouth to the stomach through the pharynx. If, somehow, the food goes through the trachea, choking may occur. Glottis is a thin tube-like structure that leads to the trachea or wind pipe. Adjacent to the windpipe lies the food pipe. When we swallow food, the epiglottis covers the glottis so that the food does not enter the windpipe through the glottis.

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Question 20:

Sneha was asked to explain what happens in our body during breathing. The paragraph that she wrote had several mistakes. Identify the mistakes she made and underline them. this is what she wrote.
During inhalation, the ribs move up and outward and the diaphragm moves in. this movement decrease the space in our chest cavity and the air rushes in. During exhalation, the ribs moves down and inward and the diaphragm moves up. This movement increases the space in our chest cavity and the air is pushed out.


During inhalation, the ribs move upwards and outwards and the diaphragm moves in. This movement increases the space in the chest cavity and allows the air to rush in. During exhalation, the ribs move downwards and inwards and the diaphragm moves out. This movement decreases the space in the chest cavity and pushes the air out.

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