Simple diffusion

Definition

Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration, occurring directly through a membrane without the need for energy input. This process is fundamental in maintaining cellular homeostasis, as it allows essential substances like oxygen and carbon dioxide to pass freely across cell membranes, facilitating vital physiological functions.

5 Must Know Facts For Your Next Test

1. Simple diffusion does not require any energy from the cell; it relies solely on the natural kinetic energy of molecules.
2. Small nonpolar molecules like oxygen and carbon dioxide typically pass through the membrane via simple diffusion due to their ability to dissolve in the lipid bilayer.
3. The rate of simple diffusion is influenced by factors such as temperature, size of molecules, and the concentration gradient.
4. Cell membranes are selectively permeable, meaning they allow certain substances to diffuse through while blocking others.
5. Simple diffusion plays a crucial role in cellular respiration and gas exchange in living organisms.

Review Questions

• How does simple diffusion contribute to maintaining cellular homeostasis?
  • Simple diffusion is essential for maintaining cellular homeostasis by allowing the passive transport of vital substances like oxygen and carbon dioxide across cell membranes. This movement occurs without energy expenditure, ensuring that cells can continuously obtain necessary nutrients and eliminate waste. By balancing concentrations of various molecules inside and outside the cell, simple diffusion helps maintain optimal conditions for cellular functions.
• Compare and contrast simple diffusion with facilitated diffusion in terms of mechanisms and types of molecules involved.
  • While both simple and facilitated diffusion are passive transport processes that move substances along their concentration gradients without using energy, they differ significantly in their mechanisms. Simple diffusion allows small nonpolar molecules to pass directly through the lipid bilayer, while facilitated diffusion requires specific carrier proteins to assist larger or polar molecules. This distinction means that facilitated diffusion can transport a broader range of substances compared to simple diffusion.
• Evaluate the impact of temperature on the rate of simple diffusion and explain why this effect is significant for cellular processes.
  • Temperature has a significant impact on the rate of simple diffusion; as temperature increases, so does the kinetic energy of molecules, leading to faster movement and a higher rate of diffusion. This is important for cellular processes because efficient gas exchange and nutrient uptake are vital for maintaining life. If temperatures are too low, diffusion rates may decrease, potentially leading to inadequate supply of essential substances or hindered removal of waste products.

Related terms

osmosis: A specific type of passive transport where water molecules move across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration.

facilitated diffusion: A process that allows molecules to cross the cell membrane with the assistance of special proteins, enabling substances that cannot easily pass through the lipid bilayer to enter or exit the cell.

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