In normal breathing, inspiration is an active process as it is brought about by the contraction of diaphragm and external intercostal muscles, while expiration is a passive process as it simply involves relaxation of inspiratory muscles.

Larynx is often called as Adam's apple. It is more prominent in males than females.

Haemoglobin consists of a protein globin and pigment haem. The four portions of iron in haem combine with molecule of oxygen. It is an easy reversible reaction to form oxyhaemoglobin
\(Hb+O_{ 2 }\rightleftharpoons HbO_{ 2 }\) 
Whereas, the complex formed by the reaction of carbon monoxide and haemoglobin is incredibly strong
Hv +CO \(\rightarrow\) HbCO
(Haemoglobin)   (Carboxy haemoglobin)
As a rsult of this strong bonding between the haemoglobin and carbon monoxide, the haemoglobin looses its affinity to oxygen thus, may lead to choking or even death.

Marine mammals (e.g, seals and whales) can make long underwater dives as they have
(i) more blood per kg of body weight
(ii) can store more oxygen in blood and muscles
(iii) have a large spleen with blood
(iv) can reduce O₂ consumption rate when underwater

At hills, the pressure of air falls and the person cannot get enough oxygen in the lungs for diffusion into the blood.Due to deficiency of oxygen, the person feels breathlessness, headche, dizziness, nausea, mental fatigue and a bluish colour on the skin, nails and lips.