Question

A resting adult requires about \(240 \mathrm{~mL}\) of pure oxygen per minute and breathes about 12 times every minute. If inhaled air contains 20 percent oxygen by volume and exhaled air 16 percent, what is the volume of air per breath? (Assume that the volume of inhaled air is equal to that of exhaled air.)

Short answer

Each breath has a volume of 500 mL.

Step-by-step solution

Calculate Oxygen Used Per Breath

The resting adult requires 240 mL of pure oxygen per minute. Breathing 12 times per minute means each breath must provide \( \frac{240}{12} = 20 \) mL of pure oxygen.

Determine Oxygen Intake from Inhaled Air

Inhaled air contains 20% oxygen. Let \( V \) be the volume of air per breath; then, \( 0.2V \) represents the volume of oxygen in the inhaled air.

Calculate Oxygen in Exhaled Air

Exhaled air is said to contain 16% oxygen. Thus, \( 0.16V \) is the volume of oxygen in the exhaled portion of the same breath.

Calculate Oxygen Consumed from the Breath

The oxygen consumed from each breath is the difference between the oxygen inhaled and exhaled: \( 0.2V - 0.16V = 0.04V \).

Equate Oxygen Consumed to Required Oxygen

Since each breath needs to supply 20 mL of pure oxygen, set up the equation \( 0.04V = 20 \) mL to find \( V \).

Solve for V

Divide both sides of the equation by 0.04: \( V = \frac{20}{0.04} = 500 \) mL.

Key concepts

Oxygen Consumption

Oxygen consumption refers to the utilization of oxygen by the body's cells for metabolic processes. Our bodies need oxygen to produce energy from the food we eat. This energy is crucial for maintaining basic bodily functions, even while at rest. For a resting adult, approximately 240 mL of pure oxygen is consumed every minute. This amount reflects the oxygen demands necessary for various bodily functions.

Understanding how much oxygen is consumed helps in determining how much air an individual needs to inhale per minute. This, in turn, can be essential for calculating medical requirements such as oxygen therapy or fitness assessments. It's also pivotal for analyzing metabolic rates and the efficiency of respiratory function.

• Provides energy required for resting metabolic functions.
• Determines the amount of air needed for sustaining life at resting states.

Breathing Rate

The breathing rate is the number of times a person inhales and exhales in a minute. For the average resting adult, this rate is about 12 breaths per minute. The breathing rate is an essential factor in determining how much oxygen is taken up by the lungs. By knowing the breathing rate, one can estimate the volume of air entering the lungs per breath.

Breathing rate can vary based on several factors like physical activity, age, health status, and emotional state. A higher rate might indicate increased demands for oxygen during exercise or stress. Conversely, a lower rate might suggest a relaxed or deep rest state. Monitoring it can give insights into a person's health and fitness level.

• Averages around 12 breaths per minute for resting adults.
• Impacts total oxygen uptake and carbon dioxide expulsion.

Inhaled Air Composition

Inhaled air comprises several gases, but oxygen is of primary interest due to its essential role in respiration. Ambient air typically contains about 21% oxygen by volume, although this figure might reduce slightly indoors.

However, for calculation purposes, inhaled air is assumed to be around 20% oxygen in most scientific and academic exercises. This composition means that when a person inhales, only 20% of the volume is oxygen that can be used by the body. This standard assumption simplifies the calculation of how much oxygen one would receive per breath, by multiplying the volume of inhaled air by the percentage of oxygen present.

• Oxygen makes up approximately 20% of inhaled air.
• Other gases include nitrogen and trace amounts of other components.
• Determines the initial oxygen available for consumption.

Exhaled Air Composition

Exhaled air differs from inhaled air primarily in its oxygen and carbon dioxide content. After gas exchange occurs in the lungs, the oxygen concentration diminishes, and carbon dioxide concentration increases.

The exhaled air usually contains around 16% oxygen. This reduction indicates that approximately 4% of the oxygen from the inhaled air is absorbed by the alveoli in the lungs for metabolic processes. Exhaled air's oxygen concentration helps calculate how much oxygen has been utilized in the body.

• Oxygen concentration in exhaled air is typically around 16%.
• Indicates respiration efficiency and metabolic activity.
• Used to calculate oxygen uptake and consumption.