Transport in Cells

Keywords

Transport, cell, diffusion, osmosis, concentration gradient, ventilation, excretion, secretion, semi-permeable, membrane, ants.

Introduction

There are different methods that use a system of transport within organisms that move cells or molecules from one place to another.

Let's take a look at some of them in detail.

Diffusion/Osmosis

Diffusion and Osmosis go together. They are often confused with one another, as they do a similar function. They both equalise the concentration of two solutions. They are also both passive transport systems, requiring no energy to process.

Diffusion can occur in any mixture, whereas Osmosis does not not. It can only occur in a mixture that requires a semi-permeable membrane. So, what is diffusion?

Well, let's look at a cup of water first. Go get a cup, and put some cold water in it. Not much, but it is able to be consumed if you were to drink it, right?

Get another cup, and fill it with hot water. This one you coud drink (please don't!) but you might scold your throat, for being too hot.

Okay, you have a hot and cold cup of water. Great. Now, get some salt or sugar. Test each cup of water with a teaspoon of each. What happens?

I'd imagine in the hot cup, the salt or sugar would dissolve into the solution quite quickly. Whereas, in the cold cup, it would take longer to dissolve.

This experiment (that's right, you've just done one) shows you that mixture of salt [or sugar] and water becomes a solution. How is this diffusion?

Well, diffusion is the process that surrounds it. You can make another mixture by using salt and sand. No matter how much you mix it together, it doesn't become anything other than salt and sand mixed together. Whereas diffusion would allow some of the concentration of the salt mix with water (as in our experiment).

Diffusion can occur in humans. When we breathe, we process the carbon dioxide (which leaves our body when we breathe out) and oxygen (which enters our blood system via red blood cells) to become their own elements or molecules. We use the oxygen to fill red blood cells, which then is transported around our bodies to help create energy for it.

Diffusion also occurs in plants. The simple process of photosynthesis uses diffusion when it attracts the sunlight. It then converts the carbon dioxide to oxygen and releases it underneath the leaf through the stomata.

Ventilation

Ventilation works with concentration gradient. It is a mass flow of gases in the lungs, along with the continuous flow of blood in the capillaries, that helps ensure there is always a higher concentration of oxygen in the alveoli (in the lungs) than in the blood.

Our natural process of breathing allows us to refresh the air in the lungs to provide it with new oxygen, and remove the carbon dioxide. This is how ventilation works. It's a mass exchange of gases.

Excretion

Yes, it really does include poo. We make a lot of waste material that has to exit our body somehow. So, when you go to the toilet, whether you are doing either of the toilet habits, you are using the excretory system to remove your body of [potentially] harmful waste product that is no longer needed in your body.

Is that it? Well, no, actually. It's not just the feces and urine that is excretory. What about when you get hot, what happens then?

Your body, when it gets too hot, reacts by allowing you to sweat. You have little pores all over your skin that allow the organ to essentially breathe, and this also allows the sweat glands to release that often salty liquid from your body. It then cools down your body to an acceptable temperature.

End Note

We know that diffusion and osmosis are similar processes that allow the movement of molecules on a concentration gradient. We also know that ventilation is a process used by the lungs for mass gas exchange. And finally, we know that exretion is the removal of waste material from an organism, and is done through various processes.