Question

Consider the idealized animal in Figure 40.4. At which sites must oxygen cross a plasma membrane in traveling from the external environment to the cytoplasm of a body cell?

Short answer

An oxygen molecule passes through a plasma membrane while entering the body at the respiratory exchange surface, circulatory entering, and exterior surface. The other site also includes interstitial fluid to the cytoplasmic fluid of a cell and exchanges chemicals with the surroundings.

Step-by-step solution

Plasma membrane

The plasma membrane refers to a biological membrane, and transported material is first to adhere to protein receptors on the exterior environment of the plasma membrane. The extracellular fluid eliminates the material that is required by the cell.

Simple diffusion 

The transportation of oxygen and carbon dioxide across the cell membrane is facilitated by simple diffusion in the direction of a concentration gradient.

Simple diffusion does not require any energy input and allows oxygen to diffuse out of the lungs' air sacs into the blood as the concentration of oxygen is more in the lungs than in the blood.

Interstitial fluid

Interstitial body fluid is the fluid that fills the spaces around cells, and this fluid helps in exchanging surfaces with cells in the biological tissue and the blood. The interstitial fluid is exchanged between the circulatory fluid such as blood to extract nutrients and eliminate toxic wastes.

The oxygen passing through the plasma membrane can be respiratory sites where an exchange of surfaces occurs, the circulatory site, and the exchange of chemicals between interstitial fluid and cytoplasmic fluid.