Cellular Respiration and Human Breathing Explained

Cellular Energy Production

Cells use energy for all their reactions and processes. These vital processes include:

• Movement
• Making new substances from small molecules
• Growth and repair
• Active transport
• Nerve impulses
• Heat production

Aerobic Respiration: Energy with Oxygen

Aerobic respiration is the release of energy using oxygen. Oxygen is carried by the blood in red blood cells within hemoglobin and diffuses into cells. Glucose also travels to the cells in the blood.

In the cytoplasm of cells, there are specific organelles called mitochondria. Oxygen diffuses into the mitochondria and is used to react with glucose to produce carbon dioxide and water. The chemical energy is transferred to a substance called ATP, which stores a small amount of energy.

The word equation for aerobic respiration is:

Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)

Anaerobic Respiration: Energy Without Oxygen

Anaerobic respiration is the release of energy without oxygen. This process occurs when oxygen supply is limited, such as during intense physical activity.

Anaerobic Respiration in Humans

If a person runs fast, breathing might not bring in enough oxygen to meet the energy demands. The body still needs to move, so glucose is only partly broken down. Only a little of the energy can be transformed into ATP. Most of the energy is left in the remaining substance called lactic acid.

The word equation for anaerobic respiration in humans is:

Glucose → Lactic Acid + Small Amount of Energy (ATP)

Lactic acid is a metabolic byproduct that can make muscles feel tired. Too much lactic acid causes cramp and must be removed quickly. Oxygen debt occurs when the muscles need extra oxygen to convert lactic acid to carbon dioxide and water. This is why runners pant heavily at the end of a race.

Anaerobic Respiration in Plants and Microorganisms (Fermentation)

In plants and microorganisms, a different substance is released instead of lactic acid: alcohol. Humans have made use of this process of anaerobic respiration, which is commonly called fermentation.

The word equation for anaerobic respiration in plants and microorganisms is:

Glucose → Alcohol + Carbon Dioxide + Some Energy (ATP)

Ventilation and Gas Exchange

Ventilation is the process of getting air into and out of the lungs, while gas exchange is the movement of gases into or out of the blood.

The Process of Inhalation

When you inhale:

1. The diaphragm contracts and flattens.
2. The rib muscles contract, moving the ribs up and out.
3. The volume of the chest cavity increases, causing the air pressure inside to decrease.
4. The internal air pressure goes below atmospheric air pressure.
5. Air rushes from the higher pressure outside the mouth into the area of lower pressure inside the lungs.

The Process of Exhalation

To get the air out of the lungs again, both the diaphragm and the rib muscles must relax. This reduces the volume of the chest cavity, increasing the internal air pressure and forcing air out.

Gas Exchange in the Lungs

In the lungs, gases can diffuse between the air in the alveoli and the blood in the capillaries. This gas exchange depends on the concentrations of gases in the alveoli and the blood.

Factors Affecting Gas Diffusion

Efficient gas diffusion in the lungs depends on several key factors:

• Large Surface Area: The larger the surface area available, the more gas can diffuse.
• Steep Diffusion Gradient: A greater difference in concentration between two areas leads to faster diffusion.
• Short Diffusion Distance: A shorter distance for gases to travel across membranes allows for quicker diffusion.