Simple diffusion

Definition

Simple diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration without the need for energy input or assistance from transport proteins. This natural tendency of molecules to spread out evenly in a given space is crucial for maintaining cellular homeostasis and facilitating the movement of essential substances across cell membranes.

5 Must Know Facts For Your Next Test

1. Simple diffusion occurs spontaneously and does not require any cellular energy (ATP) to take place.
2. It is primarily involved in the movement of small, nonpolar molecules like oxygen and carbon dioxide across the cell membrane.
3. Factors such as temperature, molecular size, and surface area can affect the rate of simple diffusion.
4. Cell membranes are selectively permeable, meaning they allow some substances to diffuse freely while restricting others based on size or polarity.
5. Simple diffusion plays a critical role in processes such as gas exchange in lungs and nutrient absorption in intestines.

Review Questions

• How does the concept of a concentration gradient relate to simple diffusion?
  • A concentration gradient refers to the difference in concentration between two areas. In simple diffusion, molecules naturally move down this gradient from an area of higher concentration to an area of lower concentration. This movement continues until equilibrium is reached, where the concentrations become equal on both sides of the membrane. Understanding this gradient is essential for grasping how substances like oxygen and carbon dioxide move across cell membranes during respiration.
• Discuss the importance of permeability in the context of simple diffusion and cell membrane function.
  • Permeability is crucial for simple diffusion because it determines which substances can pass through the cell membrane and how easily they can do so. The lipid bilayer's structure allows small, nonpolar molecules to diffuse freely, while larger or charged molecules may require specific channels or carriers. This selective permeability is vital for maintaining cellular homeostasis, as it controls the entry and exit of essential nutrients and waste products.
• Evaluate how temperature and molecular size influence the rate of simple diffusion across a cell membrane.
  • Temperature and molecular size significantly impact the rate of simple diffusion. Higher temperatures increase kinetic energy, causing molecules to move faster and thus diffuse more quickly across membranes. Conversely, larger molecules face greater resistance when trying to move through the membrane, slowing down their diffusion rate. This interplay between temperature and size highlights the dynamic nature of diffusion and its dependence on physical factors, ultimately affecting how cells interact with their environment.

Related terms

concentration gradient:

A difference in the concentration of a substance across a space, which drives the movement of molecules during diffusion.

permeability: The ability of a membrane to allow substances to pass through it, influencing how effectively simple diffusion occurs.

osmosis:

The specific type of simple diffusion that involves the movement of water molecules across a selectively permeable membrane.