Diffusion:
Diffusion is the passive movement of particles or molecules from an area of higher concentration to an area of lower concentration, down the concentration gradient. It is the random motion of particles. This process continues until equilibrium is reached, resulting in an even distribution of particles throughout the available space.
In biological systems, molecules exhibit constant movement. Whether they are part of a gas, liquid, or dissolved in a solution like sugar in water, molecules tend to spread out evenly to fill all available space due to this movement. This fundamental process is known as diffusion. In organisms, where substances often need to traverse cell membranes, diffusion plays a crucial role
For instance, consider a scenario where a cell has a higher concentration of molecules, such as oxygen, outside compared to inside. This concentration gradient prompts the molecules to diffuse into the cell until equilibrium is achieved. However, whether diffusion occurs depends on the permeability of the cell membrane. Fortunately, small molecules like water (H2O), carbon dioxide (CO2), and oxygen (O2) can easily pass through the cell membrane, facilitating diffusion and balancing the concentration of these molecules inside and outside the cell.
Importance of Diffusion:
Gasses:
Oxygen Uptake in Respiration:
Most living organisms require a constant supply of oxygen for respiration. Oxygen moves into organisms through diffusion down a concentration gradient.
Small animals with a high surface area to volume ratio can absorb oxygen through their body surface, while larger animals utilize specialized gas exchange organs such as lungs or gills. These organs provide a large surface area for efficient gas exchange.
A circulatory system is essential for larger animals to transport oxygen from gas exchange organs to cells throughout the body.
Similarly, carbon dioxide, a byproduct of aerobic respiration, is removed from organisms by diffusion.
Photosynthesis in Plants:
Photosynthetic plants require carbon dioxide for the synthesis of carbohydrates. Carbon dioxide diffuses through stomata in the leaves into the air spaces in the mesophyll, reaching the palisade cells where photosynthesis primarily occurs.
Oxygen produced during photosynthesis, as well as water vapor from the transpiration stream, diffuses out of the leaf through stomata.
Rates of Diffusion:
Molecules and ions in liquids and gasses exhibit random movement driven by kinetic energy derived from their motion. The rate of diffusion through a cell wall or membrane is influenced by various factors, including:
Surface area available for diffusion
Temperature
Difference in concentration inside and outside the cell
Distance the molecules need to travel.
Surface Area:
Surface area refers to the total area available for diffusion to occur. In biological systems, a larger surface area provides more space for molecules to interact and diffuse. For example, in organisms with specialized gas exchange organs like lungs or gills, an increased surface area allows for efficient exchange of gasses such as oxygen and carbon dioxide between the organism and its environment. Similarly, in cells, microvilli and other cellular protrusions increase the surface area of the cell membrane, facilitating the uptake of nutrients and removal of waste products through diffusion.
