(a) Smoking is very injurious for the respiratory system. It harms lungs.
(i) It causes blockage in the respiratory tract.
(ii) It leads to lung cancer.
(iii) It can cause disease like asthma and heart diseases.
(b) Yes, smoking affects people who are passive smokers, i.e. those present nearby smokers.
(c) Yes, the people should bot smoke in public areas as it can cause discomfort to others. The values we understand are obedience, respect elders and healthy habits.

The fishes have special type of organs for respiration called gills. These gills absorbs oxygen dissolved in water and through blood vessels, this oxygen is passed to all the parts of the body. The amount of dissolved oxygen is comparatively less in water than the amount of oxygen in air. Therefore, the rate of breathing is also high in aquatic animals.
If we add warm water, to the aquarium the dissolved oxygen will dissociate and move into the atmosphere again, leaving the least percentage of oxygen into the water (as it is known that the solubility of gases in water goes down as the temperature rises). Therefore, fishes will have difficulty in breathing in the absence of oxygen and will die.

(a) Due to extensive exercise, formation of lactic acid occurred as muscles starts to respire anaerobically.
(b) Yes, breathing rate will be faster. Normally we are breathing at a slower rate but during physical activities, to make sufficient amount of O₂ reaching cells we breathe faster.
(c) The body starts respiring anaerobically in the absence of sufficient oxygen. Glucose is partially broken into lactic acid which causes body cramps. Values learned - We should not force ourselves exercise but not over burn yourself discipline.

(a) Animals that can breathe only through skin are earthworm and leech.
(b) Animals that can breathe through skin as well as through lungs are frogs.
(c) Animals that can breathe through lungs are buffaloes, human, and dolphins.
(d) Animals that can breathe through gills are tadpole and fish.
(e) Animals that can breathe through spiracles and tracheae are grasshopper, cockroaches, ants, housefly and mosquito.

(a) Figure A indicates inhalation and figure B indicates exhalation.
(b) Movement of air, diaphragm and ribs are indicated in below figure

(a) Respiration is the process of breakdown of food to produce energy for performing various functions. It involves two major steps:
(i) Inhalation is the process of taking in of air which is rich in oxygen, inside our body.
(ii) Exhalation is the process of giving out of air which is rich in carbon dioxide from our body to the external environment.
(b) The number of times a person breathes, in a minute is called as breathing rate. An adult human being can inhale or exhale 15-18 times in a minute. It is the average breathing rate of an adult human being. Breathing rate is not constant always.

(a) Exhalation process of respiration is being tested in the activity.
(b) The lime water in test tube B turns milky but water in test tube A remains unchanqed Because CO₂ is present in the exhaled air, it mixes with lime water in test tube B and turns it milky.

During day, plants photosynthesise in the presence of sunlight and uses CO₂ produced during respiration. During this process O₂ is released as a byproduct and a balance between O₂ and CO₂ is maintained in the atmosphere. But in the night. plants do not photosynthesise. Plants are unable to use CO2 during night and produces CO₂ and takes O₂ during respiration. This leads to the increase in the proportion of CO₂ in the air.
So, if one sleeps under a tree at night. he will have problems in breathing as the amount of CO₂ in the air around will certainly be more than oxygen. Therefore, it is not advisable to sleep under trees during night because the person will suffer from suffocation and feel excess weight on chest.

(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 anaerobic respiration in the muscle cells after heavy exercise or running. After heavy exercise, we require large amount of energy.
To produce more energy to meet the oxygen requirement of muscles, muscle cells perform anaerobic respiration for a short duration. Lactic acid is formed due to partial breakup of glucose. It gets accumulated in the muscle cells and causes pain and muscle cramps.
(b) The massage or hot water bath gives the relief from muscle cramp or pain, because it improves the circulation of blood leading to increase supply of oxygen to the muscle cells . It helps in complete breakdown of lactic acid into carbon dioxide and water

(a) The plants do not possess any respiratory system still plants respire. The various parts of the plants like leaves, roots, etc., carry out respiration independently.
These parts take in oxygen from air in different manner and utilise it to obtain energy and give out CO₂, The leaves of plants possess tiny pores on their surface which is called as stomata. The gaseous exchange during respiration takes place through their stomata.
(b) Roots of the plants respire under the ground. Root cells get oxygen from the air present in the space between the soil particles.
There are several root hairs present on the roots of a plant.
The oxygen from the air (between soil particle) diffuses into root hair and reaches to the cells of the roots. This oxygen is utilised for respiration.