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Q.1 Boojho noticed that when he released his breath after holding it for some time, he had to breathe heavily. Can you tell him why it was so? (Page 110)
Ans. Because we need extra energy. So, we need to breathe heavily after holding it for some time.
Q.2 Paheli wants to know why we yawn when we are sleepy or drowsy. (Page 111)
Ans. Because when we feel sleepy or drowsy our breathing rate slows down. Hence, we yawn at that time.
Q.3 Boojho wants to know how much air a person can hold in the lungs. (page 114)
Ans. The average total capacity of an adult male is around 6 litres of air.
Q.4 Boojho wants to know if cockroaches, snails, fish, earthworms, ants and mosquitoes also have lungs. (page 115)
Ans. Snails, fish have lungs but lungs are absent in earthworm, ants and Cockroach.
Q.5 Boojho has seen in television programmes that Whales and dolphins often come up to the water surface. They even release a fountain of water sometimes while moving upwards. Why do they do so? (Page 116)
Ans. Whales and dolphins take in air during inhalation. They exhale out the air on the surface. The water vapour condenses and we see the condensed water vapour as the fountain.
Q.6 Paheli wants to know whether roots, which are underground also take in oxygen? If so , how? (Page 116)
Ans. Yes, roots take up air from the air spaces present between the soil particles.
Q.1 Why does an athlete breathe faster and deeper than usual after finishing the race?
Ans. During the race,  an athlete has to run very fast. The demand for energy at that time increases, which increases the demand for more supply of oxygen. Thus, athlete has to breathe faster and deep to inhale more oxygen.
Q.2 List the similarities and differences between aerobic and anaerobic respiration?
Ans. Similarities : Both aerobic and anaerobic respiration produce energy and give out carbon dioxide.
Differences : Aerobic respiration require oxygen while anaerobic respiration does not require oxygen. In aerobic respiration large amount of energy is released while in anaerobic respiration small amount of energy is released.
Q.3 Why do we often sneeze when we inhale a lot of dust-laden air?
Ans. We sneeze to get rid of the unwanted particles like dust from air. It allows only clean and dust free air to enter our body.
Q 4 Take three test-tubes. Fill 3/4 of each with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of CO2?
Ans. Test- tube A.
Q.5 Tick the correct option :
(i) In cockroaches, air enters the body through:
(a) lungs (b) gills (c) spiracles (d) skin.
(ii) During heavy exercise, we get cramps in the legs due to the accumulation of:
(a) carbon dioxide (b) lactic acid 
(c) alcohol               (d) water.
(iii) Normal range of breathing rate per minute is an average adult person at rest is :
( a) 9-12 (b) 15-18 (b) 21-24 (d) 30-33.
(iv) During acceleration, the ribs :
(a) move outwards (b) move downwards 
(c) move upwards  (d) do not move at all.
Ans. (i) (c) ;(ii) (b); (iii) (b); (iv) (b).
Q.6 Match the items in Column I with those in Column II :
Column IColumn 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) Tracheae
Ans (a) (iii) ;(b) (iv); (c) (i); (d) (v); (e) (ii); (f) (vi).
Q.7 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) During heavy exercise the breathing rate of a person flows down. (T/F)
(ii) Plants carry out photosynthesis only during the day and respiration only at night. (T/F)
(iii) Frogs breathe through their skins as well as their lungs. (T/F)
(iv) The fishes have lungs for respiration. (T/F)
(v) The size of the chest cavity increases during inhalation. (T/F)
Ans. (i) False (F); (ii) False (F); (iii) True (T); (iv) False (F); (v) True (T).
Q.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, downward, or along the diagonals. Find the words for your respiratory system. Clues about those words are given below the square.
Table (Page no. 119)
(i) The air tubes of insects
(ii) Skeletal structures surrounding chest cavity
(iii) Muscular floor of chest cavity
(iv) Tiny pores on the surface of 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 tracheal system.
Ans. (i) Trachea; (ii) Rib; (iii) Diaphragm; (iv) Stomata; (v) Spiracles; (vi) Lung; (vii) Nostrils; (viii) Yeast; (ix) Ant.
Q.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 air is higher than that on the ground.
(d) The pressure of air is higher than that on the ground.
Ans. (b) The amount of air available to a person is less than that available on the ground.

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