The role of diffusion in and within cells

 

What is diffusion?

In scientific terms, DIFFUSION is the MOVEMENT OF PARTICLES from a region of HIGH CONCENTRATION to a region of LOW CONCENTRATION.

Diffusion is a passive process, it does not require any energy for it to happen.

 

The easiest kind of diffusion is when different gases diffuse through each other.  For example, it happens when a perfume smell spreads through out the air in an enclosed area.  Likewise, diffusion of gases also take place in the leaves.

 

 

Exchange of gases in the Lungs

 

Breathing is a gas exchange mechanism.  Your Lungs help to do just that!  They contain millions of  tiny air pockets called ALVEOLI (air sacs)  which are adapted to maximise the diffusion of carbon dioxide and oxygen (see diagram below).  Alveoli  are good at gas exchange because they have:

• a large surface area.  If all the air sacs were flattened out, they would cover an area of 100m2
• moist surface which speed up diffusion.
• very thin walls which makes diffusion quicker.
• lots of blood capillaries to carry the gasses.
• the blood capillaries help the diffusion O₂ and CO₂ as their walls are only one cell thick.

In the alveolus (single air sac) oxygen passes from a high concentration (loads of oxygen) through the thin wall into the blood capillary where there is a low concentration (very little oxygen) .  This is called diffusion, because oxygen is moving from high concentration to low concentration.  When blood returns to lungs it has high concentration of carbon dioxide, so CO₂ diffuses out of the blood into the alveolus.

 

Active Transport Uptake

 

⚗️ Knowledge Check: Diffusion

Test your understanding of how particles move and why it matters in biology.

1. Diffusion occurs because particles are always:

• Stationary and fixed
• Moving randomly due to kinetic energy
• Attracted to low-pressure zones

2. In which state of matter does diffusion happen most quickly?

• Solids
• Liquids
• Gases

3. Which of the following would DECREASE the rate of diffusion?

• Increasing the temperature
• Lowering the concentration gradient
• Increasing the surface area

4. In the lungs, oxygen moves from the alveoli into the blood. What is this an example of?

• Active Transport
• Gas Exchange via Diffusion
• Osmosis

5. What does 'Net Movement' mean in diffusion?

• Particles only move in one direction
• The overall movement of particles toward the lower concentration area
• Particles moving through a fishing net

Check Your Answers

1. Moving randomly (The movement is constant and random).
2. Gases (Particles in gases have more energy and space to move).
3. Lowering the concentration gradient (A smaller difference in concentration slows movement).
4. Gas Exchange (Specifically, oxygen moves from high concentration in lungs to lower in blood).
5. Overall movement (While individual particles move everywhere, the majority move toward the 'low' side).

 

Summary:

 

• Particles move from high to low concentrations by diffusion.
• Diffusion is a natural process that does not need energy.
• Oxygen, carbon dioxide and glucose diffuse in and out of cells.