Why do human beings have difficulty breathing at high elevations?A) O2 makes up lower percentage thereB) The temperature is higher thereC) The barometric pressure is higher thereD) Pressure of O2 is lower there.

Human beings have difficulty breathing at high elevations due to the lower pressure of oxygen (Option D). Here’s a detailed explanation:

At higher altitudes, the atmospheric pressure decreases. While the percentage of oxygen in the air remains about 21%, the total air pressure is lower, which results in a lower partial pressure of oxygen. The partial pressure of oxygen refers to the amount of oxygen available for the body to absorb from the air. As the partial pressure of oxygen decreases, the body receives less oxygen with each breath. This is why people experience difficulty breathing, feel short of breath, or may suffer from altitude sickness at high elevations.

To clarify the options: A) O2 makes up a lower percentage there - Incorrect. The percentage of oxygen in the air remains constant at 21%, no matter the elevation. B) The temperature is higher there - Incorrect. Temperature varies, but it’s not the primary factor affecting oxygen levels at high altitudes. C) The barometric pressure is higher there - Incorrect. At high elevations, barometric pressure is lower, not higher. D) Pressure of O2 is lower there - Correct. The lower atmospheric pressure at high altitudes leads to a reduced partial pressure of oxygen, which is the main cause of difficulty in breathing.