Respiration and Gas Transport

The placenta facilitates the exchange of materials between mother and fetus. While oxygen and nutrients move toward the fetus, metabolic waste products move from the fetus to the mother for excretion.

Obligate anaerobes cannot tolerate oxygen because they lack the enzymes necessary to neutralize toxic oxygen byproducts. Therefore, they require an environment with no oxygen.

Carbon monoxide binds to hemoglobin with much greater affinity than oxygen, effectively displacing O2 and reducing the blood's oxygen-carrying capacity. It doesn't shut down the nervous system, destroy the respiratory system, or kill red blood cells directly.

The process described is cellular respiration. Diffusion is simply the movement of molecules from an area of higher concentration to lower concentration.

Cellular respiration is the metabolic process where cells break down glucose using oxygen to produce energy, releasing carbon dioxide and water as byproducts.

Gas exchange occurs in the lungs between the alveoli (air sacs) and the surrounding pulmonary capillaries. Oxygen enters the blood and carbon dioxide leaves it.

When muscles work harder than the oxygen supply can support, they switch to lactic acid fermentation. The accumulation of lactic acid is associated with the burning sensation felt in muscles during intense exercise.

The prefix 'an-' means without, and 'aerobic' refers to oxygen. Thus, anaerobic respiration is the process of generating energy without the use of oxygen.

Blood is red because of hemoglobin, an iron-rich protein in red blood cells that binds to oxygen and reflects red light.

The lungs are highly efficient at removing volatile acids like carbonic acid; they can eliminate the equivalent of approximately 30 liters of carbonic acid per day through the expiration of CO2.

Carbonic acid (H2CO3) is a volatile acid. An excess of H2CO3 in the blood, typically caused by hypoventilation, leads to respiratory acidosis.

The bicarbonate buffer system maintains a normal arterial blood pH of 7.4 by keeping a ratio of 20 parts bicarbonate to 1 part carbonic acid.

Oxygen moves from the alveoli into the blood via simple diffusion, which is a type of passive transport that does not require energy.

In the alveoli, the oxygen is continuously absorbed by the blood and CO$ _{2}$ is continuously added by the blood. So, the alveolar air has more CO$ _{2}$ concentration than the expired air.

Inhaled air contains more oxygen used to create energy and less CO$ _2$. It contains 21% O$ _2$, 0.04% CO$ _2$ and 79% Nitrogen. Exhaled air contains 16% O$ _2$, 4% CO$ _2$ and 79% Nitrogen. Thus, option C is correct.