Ch 2Breathing and Exchange of Gases — Class 12 Zoology, concept-first.

Every cell in the body constantly breaks down fuel molecules — glucose, amino acids, fatty acids — to release the energy it needs for its everyday activities.

Every living animal must take in oxygen and get rid of carbon dioxide, but the way this gas exchange is carried out is not the same across the animal kingdom.

The human respiratory system is a continuous passage that carries outside air deep into the lungs, where the actual exchange of gases happens.

Breathing is the mechanical process of moving air into and out of the lungs. It has two stages: inspiration, in which outside air is pulled in, and expiration, in which the air inside the alveoli is p…

When we breathe in and out, the amount of air moved is not always the same — a quiet breath moves only a little air, while a forced breath moves a great deal more.

Once air reaches the alveoli, the gases must move between air and blood, and later between blood and the body's tissues.

Blood is the medium that carries respiratory gases around the body — oxygen from the lungs to the tissues, and carbon dioxide from the tissues back to the lungs.

Oxygen does not travel through the blood on its own; most of it is carried bound to a special pigment inside the red blood cells.

Carbon dioxide produced by the tissues has to be carried back to the lungs to be breathed out. Unlike oxygen, it is transported in more than one way, and its movement is closely tied to the same press…

Breathing is not fixed at one steady pace — the body constantly adjusts it to match what the tissues need at the moment, whether at rest or during exertion.

The respiratory system, like any other, can be affected by disorders that reduce its ability to move air and exchange gases. Three are highlighted here.

Cells use oxygen to carry out metabolism and generate energy, and in the process they produce carbon dioxide, a harmful waste that must be removed.

Higher-order thinking / exemplar-style practice problems.