How does a steeper concentration gradient affect the rate of diffusion?

A steeper gradient increases the rate of diffusion. This is because a larger difference in concentration between two areas creates a stronger 'driving force' for the net movement of particles.

What is the difference between simple diffusion and facilitated diffusion?

Simple diffusion occurs when small or non-polar molecules pass directly through the cell membrane. Facilitated diffusion involves larger or polar molecules passing through specific protein channels or carriers.

Why does increasing the temperature speed up diffusion?

Higher temperatures provide particles with more kinetic energy. This causes them to move faster and collide more often, resulting in a quicker spread from high to low concentration areas.

What happens to the net movement of particles when dynamic equilibrium is reached?

The net movement becomes zero. While individual particles continue to move randomly in all directions, there is no overall change in concentration because the movement is balanced.

What is a common misconception regarding particle movement at equilibrium?

A common error is thinking that particles stop moving entirely. In reality, they continue to move due to their kinetic energy, but they remain evenly distributed.

How does the thickness of a membrane affect the rate of diffusion?

The rate of diffusion is inversely proportional to the thickness of the membrane. A thicker membrane increases the distance particles must travel, which slows down the overall rate of exchange.

Why is a large surface area beneficial for gas exchange in the lungs?

A large surface area provides more space and 'entry points' for gas molecules to cross the membrane. This maximizes the number of molecules that can diffuse at any given time.

What is the difference between diffusion and active transport?

Diffusion is a passive process that moves substances down a concentration gradient without energy. Active transport requires energy (ATP) to move substances against a concentration gradient.

How does particle mass influence the rate of diffusion?

Smaller, lighter particles generally diffuse faster than larger, heavier ones. This is because, at a given temperature, lighter particles achieve higher velocities than heavier ones.

What error occurs if you confuse 'diffusion' with 'osmosis' in an exam?

The error is failing to specify the substance; osmosis refers strictly to the movement of water molecules across a partially permeable membrane, while diffusion applies to any particle.

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Factors that Affect Diffusion

Summary

Diffusion is the passive net movement of particles from a region of higher concentration to a region of lower concentration. The rate at which this process occurs is governed by several physical and environmental variables, including the steepness of the concentration gradient, the thermal energy of the system, and the physical dimensions of the exchange surface.

1. Definition & Core Concepts

Diffusion is defined as the net movement of particles (atoms, ions, or molecules) from an area of high concentration to an area of low concentration until they are evenly distributed.
It is a passive process, meaning it does not require an external energy source like ATP; instead, it relies on the intrinsic kinetic energy of the particles themselves.
The movement is described as 'net' because while individual particles move randomly in all directions, the overall flow is toward the area of lower concentration.
This process continues until dynamic equilibrium is reached, where particles are spread evenly but continue to move with no further change in concentration.

Diagram showing a concentration gradient with particles moving from a high-density area to a low-density area across a boundary.

2. The Concentration Gradient

The concentration gradient refers to the difference in the number of particles between two adjacent regions.
A steeper gradient (a larger difference in concentration) results in a faster rate of diffusion because there is a higher probability of particles moving into the less crowded area.
Mathematically, the rate of diffusion is often considered proportional to the gradient: $Rate \propto \Delta C$ .
As the concentrations on both sides become more similar, the gradient 'flattens,' and the rate of net movement slows down.

3. Temperature and Kinetic Energy

4. Surface Area and Diffusion Distance

5. Key Distinctions

6. Exam Strategy & Tips