Factors Affecting the Rate of Diffusion

“Alright students, let’s delve into the factors that influence how quickly diffusion happens, which is referred to as the ‘rate of diffusion’. We can think of three big players in this game:

First up, we’ve got ‘Temperature’. Imagine you’ve just had a cup of tea; the heat from the tea makes you feel a bit more energetic, doesn’t it? Similarly, as the temperature goes up, particles gain more energy, causing them to move about faster. So, increasing the temperature means particles will diffuse faster.

Next, we have what’s called the ‘Concentration Gradient’. This is just a fancy way of talking about the difference in concentration between two places. The bigger the difference, the faster the diffusion. For instance, if there’s a lot of a particular substance outside a cell and not much inside, particles will hurry into the cell.

Lastly, there’s ‘Surface Area’. Think of it like the number of doors into a building. If there are more doors (or a larger surface area), more people (or particles) can go in and out at the same time. Therefore, a bigger surface area allows for faster diffusion.

Now, let’s talk size. Single-celled organisms like amoeba are quite small but have a massive surface area compared to their volume. That means they have a high ‘surface area to volume ratio’, which is super useful because they can rely on diffusion alone to get substances in and out.

Let’s imagine this with two cube-shaped organisms. If one cube has sides of 1 metre each, its surface area to volume ratio is 6:1. If the other cube is bigger, with sides of 2 metres each, its ratio drops to 3:1. What this shows is that as organisms get bigger, they face a challenge: their surface area isn’t growing as fast as their volume.

This can be a big deal. Imagine being in the middle of a crowded concert and trying to get some fresh air. It’s hard, right? Similarly, for big, multicellular organisms, many of their cells are too far from the surface, making it tricky for oxygen to reach them just by diffusion.

But nature is pretty smart. Big organisms, like us humans, have come up with solutions. Firstly, they have special structures, like our lungs, with huge surface areas for exchanging gases. And secondly, they have transport systems, like our blood, to carry substances all around the body.

And there we have it! The crucial factors and challenges of diffusion and how nature tackles them.”

The rate of diffusion is influenced by several factors. Three main factors are:

  • TemperatureIncreasing the temperature also increases the rate of diffusion. This is because the particles have more kinetic energy, so they move faster
  • Concentration Gradient (the difference in concentration) – Increasing the concentration gradient will increase the rate of diffusion. For example, if there is a higher concentration of a substance outside a cell than inside it, then the particles of the substance will diffuse into the cell.
  • Surface AreaAs you increase a membrane’s surface area, the diffusion rate also increases. This is because the same volume of substance has a greater area to diffuse across.

Surface Area to Volume Ratio

Single-celled organisms, such as amoeba, have huge surface areas for their volume. In other words, they have high surface area to volume ratios. So, they can use diffusion to transport substances in and out of their cell.

Calculating the surface area to volume ratio

Let’s imagine two organisms shaped like cubes. The length of each side is 1 metre for the first cube and 2 metres for the second.

For the first cube, the surface area to volume ratio is 6:1, while for the second cube, the ratio decreases to 3:1. So, as the size of the organism increases, the surface area to volume ratio decreases.

This poses a problem for multicellular organisms whose surface area is insufficient for their cell volume. Many cells are positioned too far from the surface for oxygen to diffuse into them effectively

Multicellular organisms solve this problem in two main ways:

  • They have unique gas exchange structures with very large surface areas
  • They have transport systems to carry substances around the body