Passive diffusion

Definition

Passive diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration without the need for energy input. This process is essential in the absorption mechanisms and nutrient transport within biological systems, allowing for the natural flow of substances across cell membranes and facilitating vital physiological functions.

5 Must Know Facts For Your Next Test

1. Passive diffusion occurs spontaneously and does not require ATP or any other form of energy, making it a cost-effective method for cells to regulate their internal environment.
2. Lipid-soluble substances, such as oxygen and carbon dioxide, easily pass through cell membranes by passive diffusion due to their ability to dissolve in the lipid bilayer.
3. Factors influencing the rate of passive diffusion include temperature, molecular size, and the steepness of the concentration gradient; higher temperatures and steeper gradients increase the rate.
4. In biological systems, passive diffusion is critical for processes like gas exchange in the lungs and nutrient absorption in the intestines.
5. While passive diffusion is efficient for small and nonpolar molecules, larger molecules often rely on facilitated diffusion or active transport to enter cells.

Review Questions

• How does passive diffusion differ from active transport in terms of energy requirements and molecule movement?
  • Passive diffusion operates without energy expenditure, moving molecules along their concentration gradient from high to low concentration. In contrast, active transport requires energy to move substances against their concentration gradient, allowing cells to accumulate nutrients or expel waste. This fundamental difference highlights how cells utilize energy efficiently to maintain homeostasis and regulate their internal environments.
• What role does selective permeability play in the process of passive diffusion within cellular membranes?
  • Selective permeability is crucial for passive diffusion as it determines which substances can cross the membrane. Membranes are designed to allow small, nonpolar molecules to diffuse freely while restricting larger or charged particles. This selective barrier ensures that essential nutrients can enter the cell via passive diffusion while maintaining control over harmful substances, contributing to the overall balance and function of cellular activities.
• Evaluate the impact of factors such as temperature and concentration gradient on the efficiency of passive diffusion in nutrient transport.
  • The efficiency of passive diffusion in nutrient transport is significantly influenced by factors like temperature and concentration gradient. Higher temperatures increase molecular motion, thus enhancing the rate of diffusion. Additionally, a steeper concentration gradient accelerates the movement of molecules from high to low concentration. Together, these factors create optimal conditions for cells to efficiently absorb nutrients and maintain metabolic processes, demonstrating how environmental variables can directly affect physiological functions.

Related terms

Concentration gradient: The difference in concentration of a substance between two regions, which drives the movement of molecules during passive diffusion.

Selective permeability: The property of cellular membranes that allows certain molecules to pass through while blocking others, crucial for regulating what enters and exits a cell.

Facilitated diffusion: A type of passive transport that involves specific carrier proteins to help move larger or polar molecules across a membrane without using energy.