Passive Diffusion

Definition

Passive diffusion is a type of transport mechanism in which molecules or ions move across a cell membrane from an area of higher concentration to an area of lower concentration, without the expenditure of cellular energy. This process occurs naturally and is driven solely by the concentration gradient.

5 Must Know Facts For Your Next Test

1. Passive diffusion is a spontaneous process that does not require the input of energy, such as ATP, to occur.
2. The rate of passive diffusion is directly proportional to the concentration gradient and the permeability of the cell membrane to the substance.
3. Passive diffusion is an important mechanism for the absorption of nutrients, such as glucose and amino acids, during the digestive process.
4. Substances that are small, uncharged, and lipid-soluble tend to have a higher rate of passive diffusion across cell membranes.
5. Passive diffusion plays a crucial role in the regulation of pH, water balance, and the movement of waste products out of cells during digestion.

Review Questions

• Explain how the concentration gradient drives the process of passive diffusion.
  • The concentration gradient is the difference in the concentration of a substance on either side of a cell membrane. Passive diffusion occurs when a substance moves from an area of higher concentration to an area of lower concentration, without the expenditure of cellular energy. The greater the concentration gradient, the faster the rate of passive diffusion. This process continues until the concentrations on both sides of the membrane are equal, and the system reaches equilibrium.
• Describe the role of passive diffusion in the absorption of nutrients during the digestive process.
  • Passive diffusion is a crucial mechanism for the absorption of nutrients, such as glucose and amino acids, during the digestive process. As food is broken down in the digestive tract, these small, uncharged, and lipid-soluble molecules are able to passively diffuse across the cell membranes of the intestinal epithelial cells. This allows the nutrients to be absorbed into the bloodstream and transported to the cells throughout the body, where they can be utilized for energy production and other metabolic processes.
• Analyze the importance of passive diffusion in the regulation of pH, water balance, and the movement of waste products during digestion.
  • Passive diffusion plays a vital role in the regulation of pH, water balance, and the movement of waste products during the digestive process. For example, the movement of hydrogen ions (H+) and bicarbonate ions (HCO3-) across cell membranes through passive diffusion helps maintain the appropriate pH levels in the digestive tract. Similarly, the passive diffusion of water molecules across cell membranes, known as osmosis, is essential for the absorption of water and the regulation of fluid balance. Finally, the passive diffusion of waste products, such as urea and carbon dioxide, out of cells and into the bloodstream allows for their elimination from the body, which is a critical aspect of the digestive system's function.

Related terms

Concentration Gradient: The difference in the concentration of a substance across a barrier, such as a cell membrane, which creates a driving force for the movement of that substance.

Permeability: The ease with which a substance can pass through a cell membrane, which depends on factors like the size, charge, and solubility of the substance.

Osmosis: The passive diffusion of water molecules across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.