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Page No 120:

Question 1:

In insects, exchange of gases takes place through

(a) spiracles
(b) gills
(c) lungs
(d) stomata

Answer:

(a) spiracles
Spiracles are the openings present on the bodies of insects through which exchange of gases takes place.

Page No 120:

Question 2:

Through which tubes does air enter the lungs from the windpipe?

(a) bronchi
(b) bronchioles
(c) alveoli
(d) trachea

Answer:

(a) bronchi
Windpipe branches into two small tubes known as bronchi, through which the air enters the lung.

Page No 120:

Question 3:

Where in the respiratory system does oxygen from the air breathed in pass into the blood?

(a) trachea
(b) bronchi
(c) bronchioles
(d) alveoli

Answer:

(d) alveoli
Oxygen from the air breathed in pass into the blood from alveoli in the lungs, which are surrounded by blood vessels.

Page No 120:

Question 4:

Which of these is not true about cellular respiration?

(a) It releases energy
(b) It occurs only during the day
(c) It utilizes oxygen and liberates carbon dioxide
(d) It occurs in all living things

Answer:

(b) It occurs only during the day
Cellular respiration is not dependent on light. It occurs all the time, both day and night.



Page No 121:

Question 1:

What is 'oxidation'?

Answer:

Oxidation is the breakdown of food (glucose) into carbon dioxide and water to release energy in the presence of oxygen.

Page No 121:

Question 2:

Why should we not overwater potted plants?

Answer:

We should not over-water potted plants because water will replace the air present in the soil and roots won't be able to breathe.

Page No 121:

Question 3:

What do you mean by the 'stomatal apparatus'?

Answer:

Stomatal apparatus refers to the stomata along with its nearby guard cells and other associated cells.

Page No 121:

Question 4:

What are the main organs of the respiratory system?

Answer:

The main organs of the human respiratory system are nostrils, trachea, bronchi and lungs.

Page No 121:

Question 5:

What happens during cellular respiration?

Answer:

During cellular respiration, the food is broken down in presence of oxygen into carbon dioxide and water to give energy.

Page No 121:

Question 6:

Why does the breathing becomes faster while doing exercise?

Answer:

Breathing becomes faster during exercise because more oxygen is inhaled and supplied to the cells. This increases the rate of breakdown of food and gives more energy that is needed for exercise.

Page No 121:

Question 5:

Which of these is true about anaerobic respiration?

(a) Oxygen is utilized
(b) Carbon dioxide is given out
(c) Amount of energy released is more than in aerobic respiration
(d) Sometimes it occurs in the human body also

Answer:

(b) Carbon dioxide is given out.
In anaerobic respiration, glucose is broken down into alcohol and carbon dioxide in the absence of oxygen.

Page No 121:

Question 6:

Exchange of gases in plants takes place through the

(a) stomata
(b) roots
(c) buds
(d) entire leaf surface

Answer:

(a) stomata
Stomata are tiny pores present on the surface of leaves through which gaseous exchange takes place in plants.

Page No 121:

Question 7:

During which process is energy released?

(a) external respiration
(b) internal respiration
(c) inhalation
(d) exhalation

Answer:

(b) internal respiration
Internal respiration, also known as cellular respiration, uses oxygen to break down food and release energy.

Page No 121:

Question 8:

Which of these is not true?

(a) Combustion is a faster process than respiration.
(b) Combustion occurs at a higher temperature than respiration.
(c) In combustion, energy is released in several steps, whereas in respiration it is released in a single step.
(d) Combustion can occur anywhere but respiration only occurs in living cells.

Answer:

(c) In combustion, energy is released in several steps, whereas in respiration, it is released in a single step.
Combustion releases energy in a single step in the form of light and heat. Whereas in respiration, energy is released in steps and is stored in the form of ATP.

Page No 121:

Question 1:

Give one-word for 'the process of release of energy by oxidation of food'.

Answer:

Cellular respiration is the process of release of energy by oxidation of food.

Page No 121:

Question 2:

Name the flap that closes the windpipe when you swallow food.

Answer:

Epiglottis is the flap that closes our windpipe when we swallow food.

Page No 121:

Question 3:

Which muscular part of the body present in the chest cavity helps air to be breathed in and out?

Answer:

Diaphragm is the muscular part of the body present in the chest cavity that helps air to be breathed in and out.

Page No 121:

Question 4:

Taking in oxygen and giving out carbon dioxide is called ___________or ____________ respiration.

Answer:

Taking in oxygen and giving out carbon dioxide is called breathing or external respiration.

Page No 121:

Question 5:

Name the pores in the stems and leaves of plants through which exchange of gases takes place.

Answer:

Stomata are the pores in the stems and leaves of plants through which exchange of gases takes place.

Page No 121:

Question 6:

In Amoeba, exchange of gases occurs by ________ through the cell membrane.

Answer:

In Amoeba, exchange of gases occurs by diffusion through the cell membrane.

Page No 121:

Question 7:

Exchange of gases on fishes occurs through gills. True of false?

Answer:

True.
In fishes, exchange of gases occurs through gills.

Page No 121:

Question 8:

During cellular respiration, the sugar molecules in food are _________ to form carbon dioxide and water.

Answer:

During cellular respiration, the sugar molecules in food are oxidised to form carbon dioxide and water.

Page No 121:

Question 9:

Respiration without oxygen is called aerobic respiration. True of false?

Answer:

False.
Respiration without oxygen is called anaerobic respiration.

Page No 121:

Question 10:

Trace the path of oxygen in humans during respiration by filling in the blanks with the main organs of the respiratory system: Nostrils and nasal cavity →__________ → __________ → lungs → __________ → __________ → cells

Answer:

Path of oxygen in humans during respiration:
Nostrils and nasal cavity  pharynx  trachea and bronchi  lungs  bronchioles and alveoli  blood  cells.

Page No 121:

Question 11:

The substance present in blood which transpotrs oxygen is _________

Answer:

The substance present in blood which transports oxygen is haemoglobin.



Page No 122:

Question 7:

What chemical reaction occurs during anaerobic respiration in yeast?

Answer:

The chemical reaction that occurs during anaerobic respiration in yeast is:
Glucose No Oxygen  Alcohol + Carbon dioxide + Energy

Page No 122:

Question 8:

An athlete suffers from muscular cramps while running a race. How can you help him overcome the cramps?

Answer:

The cramps can be overcome by massaging the affected part or having hot water bath. These methods increase the blood circulation and the supply of oxygen in the body.

Page No 122:

Question 1:

Name and explain in one sentence each, the two main processes of respiration.

Answer:

The two main processes of respiration are as follows:

  1. Breathing or external respiration: This is the process of taking in oxygen-rich air and giving out carbon dioxide-rich air.
  2. Cellular respiration or internal respiration: This is the process of breakdown of food in the presence of oxygen into carbon dioxide and water to release energy.

Page No 122:

Question 2:

How does exchange of gases occur in the following:

(a) fish
(b) cockroach

Answer:

(a) Fish: The exchange of gases in fishes takes place through gills. Gills have large number of filaments supplied with thin blood capillaries. Water enters through the mouth and passes over the gills. Oxygen is absorbed by blood in the capillaries and carbon dioxide is given out through its walls.

(b) Cockroach: The exchange of gases takes place through spiracles. Oxygen-rich air enters the body through spiracles and reaches all parts of the body via trachea (respiratory tube). Trachea is further branched into tracheoles.

Page No 122:

Question 3:

How do the nostrils contribute to the process of breathing?

Answer:

When we breathe in air, it passes through our nostrils. The slimy mucus present in it moistens the air. The inner lining of nose secretes mucus. The blood circulating in the nose makes the air warm. The mucus and hair present in the nostril catch the dirt, dust and disease-causing germs. Thus, they cannot enter respiratory system.

Page No 122:

Question 4:

Draw a labelled diagram of the apparatus you will use to show that heat is produced during respiration in seeds. Why are two flasks used in the experiment?

Answer:

Two flasks are used in the experiment (one containing the germinating seeds and other containing the boiled seeds) to show that heat is produced during respiration. Respiration occurs in germinating seeds, but not in boiled seeds. The thermometer inserted in the flask containing germinating seeds shows higher temperature than the one inserted in the flask containing boiled seeds. This shows heat is produced during respiration.


Page No 122:

Question 5:

What happens to the air breathed in, once it reaches the lungs?

Answer:

Once the air is breathed in, it reaches the lungs and passes in to bronchioles (small tubes). At the end of bronchioles, tiny air sacs called alveoli are present. Air from bronchioles reaches the alveoli. Alveoli are surrounded by blood vessels. Here, exchange of gases between blood and air sacs takes place. The oxygen present in the breathed air enters the blood present in blood vessels and carbon dioxide present in the blood goes out into the alveoli. Thus, exchange of gases takes place in the air once it reaches the lungs.

Page No 122:

Question 6:

Explain, with the help of a diagram, the structure of human lungs, and how exchange of gases occurs in the lungs.

Answer:

Human lungs consist of small tubes, bronchioles and tiny air sacs known as alveoli (about 300 million in each lung).


 
Exchange of gases in lungs:
The air breathed in reaches the air sacs that are surrounded by blood vessels. These blood vessels transfer the oxygen present in the air to the blood. The carbon dioxide present in the blood passes to the air sacs.

Page No 122:

Question 7:

How are combustion and cellular respiration similar to each other? In what ways are they different?

Answer:

Combustion and cellular respiration are similar to each other because at the end of both processes heat and energy are released.

Differences between them:

Combustion Respiration
It is a fast process. It is a slow process.
It takes place only at high temperature. It takes place at body temperature.
It can happen anywhere. It can take place only in living cells.
It is a single-step process, and energy is released in the form of heat and light. It is a multi-step process, and energy is stored in the form of ATP.

Page No 122:

Question 8:

How will you show that exhaled air has more carbon dioxide than inhaled air?

Answer:

Carbon dioxide turns lime water milky. Based on this principle, experiment can be designed to show that exhaled air has more carbon dioxide than inhaled air.

  • Take two test tubes half filled with lime water.
  • With the help of glass tubes, clips and stoppers having two holes, set up an apparatus as shown below:
  • The middle rubber tube is used to breath in and out through the mouth.
  • Suck air through the rubber tube and open clip X and close clip Y. The inhaled air passes through the lime water present in test tube A. Now, exhale through the tube again and close clip X and open clip Y. The exhaled air passes through the lime water in test tube B.
  • The lime water in test tube B turns milky. This shows that exhaled air has more carbon dioxide.

Page No 122:

Question 9:

What is the difference between breathing and cellular respiration?

Answer:

Differences between breathing and cellular respiration:

Breathing Cellular Respiration
It is a physical process in which exchange of gases takes place. It does not involve any chemical reaction. It is oxidation of food, thus involves a chemical reaction.
It occurs outside the cells. It occurs inside the cells.
No energy is liberated in the process. Energy is liberated during the process.

Page No 122:

Question 10:

What is anaerobic respiration? Does it occur in the human body also?

Answer:

The breakdown of glucose to obtain energy in the absence of oxygen to give carbon dioxide and alcohol is termed as anaerobic respiration. Several organisms such as yeast and bacteria can live without oxygen as they carry out anaerobic respiration.
Yes, anaerobic respiration occurs in the human body also. During strenuous activities, body needs more energy but cannot get enough oxygen. Thus, anaerobic respiration occurs in the muscle cells to provide additional energy.

Page No 122:

Question 11:

Why do we sometimes suffer from muscle cramps while exercising?

Answer:

Cramps occur while exercising because of accumulation of lactic acid in the muscle cells. During exercise, body needs more energy, but it cannot get more oxygen for oxidation of food and for providing energy. The additional energy in muscle cells is provided by anaerobic respiration in which partial breakdown of glucose into lactic acid takes place. This lactic acid accumulates in muscle cells and causes cramps.

Page No 122:

Question 1:

Is it wise to sleep under a tree

(a) during the day
(b) at night

Give reasons

Answer:

(a) It is wise to sleep under a tree during the day. During day, plants take up carbon dioxide for photosynthesis and give out oxygen. Humans require oxygen for respiration. Therefore, while sleeping under a tree during daytime, one gets oxygen-rich air.

(b) On the other hand, during night, plants also respire. They take up oxygen and give out carbon dioxide. Therefore, if one sleeps under a tree during night, he/she will get oxygen-deficient air.

Page No 122:

Question 2:

A person put warm water in an aquarium, thinking that the fish would be more comfortable in it. However, the fish died. What can be the reason for this?

(HINT: the solubility of a gas in water goes down as its temperature increases)

Answer:

A fish needs the dissolved oxygen in water for respiration. Upon an increase in temperature, the solubility of oxygen in water decreases. The fish cannot get enough oxygen for respiration and hence dies.

Page No 122:

Question 3:

When you run, your breathing becomes faster as you need more oxygen. But why does your rate of heartbeat also increase?

Answer:

Body needs more oxygen during running and oxygen is carried by blood to all the parts of the body. Heart needs to pump more blood, carrying oxygen, to all the body parts during running. In order to supply more blood, the heart rate also increases during running.

Page No 122:

Question 4:

Why do plants not need a respiratory system?

Answer:

Plants have tiny pores called stomata on the surface of their leaves and stems. The exchange of gases in plants occurs through these pores. Thus, they do not need a respiratory system.

Page No 122:

Question 5:

If you hold your breath for some time and then release it, you have to breathe heavily after that. Why?

Answer:

The supply of oxygen in the body is withheld if we hold our breath. Body needs oxygen for oxidation of food in order to provide energy for all other processes. Holding our breath cuts down the supply of oxygen. After releasing it, we need to breathe heavily in order to take more oxygen which is needed by our body.

Page No 122:

Question 6:

Why do you think we yawn when we are sleepy or drowsy?

Answer:

When we are sleepy or drowsy, we need more energy and hence more oxygen. In order to draw more oxygen, we yawn.

Page No 122:

Question 7:

Why do mountaineers climbing high mountains carry oxygen cylinders with them?

Answer:

As one goes up from plains to mountains, the amount of oxygen present in the air decreases. On mountains, one cannot get enough oxygen through the normal breathing process. Thus, mountaineers need to carry oxygen cylinders with them to get continuous supply of oxygen.



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