(i) The cramps occur when muscle cells respire anaerobically. The partial break down of glucose produces lactic acid, accumulation of which causes muscle cramps.
(ii) Hot water bath improves circulation of blood. As a result, the supply of oxygen to the muscle cells increases and complete breakdown of lactic acid occurs to form carbon dioxide and water.
(iii) Apart from his profession Mr. Sharma is caring and conscious about his son, so he gave the perfect advice to him to get relief from fatigue.

We take air through our nostrils. When we inhale air, it passes through our nostrils into the nasal cavity. From nasal cavity the air reaches our lungs through the wind pipe. Lungs are present in the chest cavity. This cavity is surrounded by ribs on the sides. A large muscular sheet called diaphragm forms the floor of the chest cavity. Breathing involves the movement of the diaphragm and the rib cage

In Yeast: Yeast gets energy through anaerobic respiration. In the absence of oxygen, glucose breaks down into alcohol and carbon dioxide
GIucose\(\xrightarrow{in\ the\ absence\ of\ oxygen}\) Alcohol + Carbon dioxide + Energy
In Muscles: Our muscles can also respire anaerobically, but only for a short time. During heavy exercise, anaerobic respiration takes place in which glucose broken into lactic acid and energy.
Glucose\(\xrightarrow[of\ O_2]{absence}\)Lactic acid + Energy

The human respiratory system have following organs:
A- Ribs
B- Trachea
C- Pharynx
D - Diaphragm
E- Lungs
F- Nasal passage
G- Oral cavity

(a) The amount of CO₂ will be the highest in jar C. It is because the mice kept under the jar will breathe out CO₂ continuously increasing its amount in the jar.
(b) The amount of CO₂ will be the lowest in jar A. It is because in jar A, CO₂ released during respiration is used by the plants, i.e. during the process of photosynthesis.

When we work hard or perform physical activity (like running, swimming, cycling), we need more energy. To fulfil the energy requirement, we breathe faster. Fast breathing helps in supply of more oxygen to our cells. Due to this, rate of breakdown of food increases and more energy is released. The rapid breakdown of food makes us to feel more hungry.

(a) Snail, as it does not breathe by means of trachea.
(b) Earthworm, because it breathes through its skin and it (does not have lungs.
(c) Fish as most fish breathe through their gills and do not have lungs.
(d) Tadpole, as it breathes through hills and do not have lungs.

Test tube A will have higher concentration of CO₂, This experiment shows the relationship between plants and animals. During breathing, snail inhales dissolved oxygen from water and releases CO_2.
Water-plant along with respiration performs another important function called photosynthesis. During photosynthesis, water-plant absorbs CO₂, prepares food and releases oxygen.
Therefore, test tube Band C have less amount of CO₂ concentration as compared to test tube A.

When we inhale dust-laden air, dirt-particles are captured within the nostrils. Sometimes, they get past the nostril hair in the nasal cavity and irritate the lining of the cavity, as a result, we sneeze. Sneezing expels these foreign particles from the inhaled air and a dust free, clean air enters in our body