Problem 10 - Biology: The Unity and Diversity of Life

Question

At high altitudes,____. a. nitrogen bubbles out of the blood b. hemoglobin has fewer oxygen-binding sites c. there are fewer \(\mathrm{O}_{2}\) molecules than at low altitudes d. both b and c

Step-by-Step Solution

Answer

The correct answer is c, there are fewer \(\mathrm{O}_{2}\) molecules at high altitudes.

Step 1: Understanding the Problem

We need to determine which statement about high altitudes is correct. Common effects of high altitude include changes in oxygen levels and their impact on the body.

Step 1: Analyze Option A

Option A suggests that nitrogen bubbles out of the blood at high altitudes. This is actually a concern for divers ascending from deep waters due to pressure changes, not for altitudes.

Step 2: Analyze Option B

Option B states that hemoglobin has fewer oxygen-binding sites. This is incorrect; the number of binding sites on hemoglobin molecules doesn't change with altitude. However, oxygen availability affects hemoglobin's ability to bind oxygen.

Step 3: Analyze Option C

Option C suggests that there are fewer \(\mathrm{O}_{2}\) molecules at high altitudes. This is correct because atmospheric pressure is lower at higher altitudes, resulting in fewer oxygen molecules being available for breathing.

Step 4: Analyze Option D

Option D states that both B and C are correct. Since we found that only C is correct, this option is partially incorrect.

Key Concepts

Oxygen Availability

As you ascend to higher altitudes, the availability of oxygen decreases. This is mainly due to the decrease in atmospheric pressure that occurs as elevation increases. At sea level, air pressure is higher, which means that oxygen molecules are more densely packed. However, as you go higher, the atmospheric pressure drops, leading to a reduced number of oxygen molecules per breath.
This reduction in oxygen molecules means that with each breath you take at a high altitude, your body receives less oxygen compared to what it would get at sea level. This can lead to hypoxia, a condition where the body or a region of the body is deprived of adequate oxygen supply.
To cope with the lower oxygen availability, the body may produce more red blood cells over time, which helps to carry more oxygen throughout the body. However, this process takes time, and initial exposure to high altitudes can make one feel dizzy or breathless.

Hemoglobin Function

Hemoglobin is a protein in red blood cells that is essential for oxygen transport in the body. One molecule of hemoglobin can carry up to four oxygen molecules, thanks to its four oxygen-binding sites. However, at high altitudes, although the number of binding sites remains the same, the lower oxygen pressure affects how hemoglobin functions.
When the body is exposed to lower oxygen levels, as seen in high altitudes, hemoglobin has a lower affinity for oxygen, enhancing its ability to release oxygen to tissues that need it most. This shift is beneficial because it ensures that even though there is less oxygen available, hemoglobin can more effectively deliver what oxygen there is to critical areas of the body.

• This adaptation does not involve a change in hemoglobin quantity but is more about how efficiently it releases oxygen.
• The body can increase its production of 2,3-bisphosphoglycerate (2,3-BPG), a molecule that helps hemoglobin release oxygen more readily to tissues.

Ultimately, these adjustments allow humans to adapt to environments where oxygen availability is naturally lower than what is required for typical activities at sea level.

Atmospheric Pressure

Atmospheric pressure is the force exerted by the weight of air in the atmosphere. It decreases with altitude due to the thinning of the air and the decrease in the column of air exerting pressure. This pressure drop has several implications for living organisms, especially regarding respiratory function.
At sea level, atmospheric pressure is about 101.3 kPa, which ensures that oxygen and other gases are sufficiently packed to meet human breathing requirements. As altitude increases, the pressure may decrease significantly, for example, dropping to about 70 kPa at 3,000 meters.

• This results in fewer oxygen molecules being available per unit volume of air, making respiration more challenging.
• Lower atmospheric pressure also means that air is less dense, which can affect the body’s ability to intake and utilize the required oxygen efficiently.

These conditions force the body to adapt by increasing breathing rate and, over time, physiological changes that assist in maintaining adequate oxygen levels, even in a decreased pressure environment.