How does a concentration affect the movement of molecules across the membrane?
Answer Hello Jessica, consider a container with a watery solution of, e.g., sugar or salt. Due to diffusion the concentration of the dissolved substance becomes the same at each place in the container a short while after introducing the substance; the individual sugar or salt particles travel in random directions which ultimately results in a uniform distribution. Introducing a membrane which divides the container into two compartments means building a barrier the particles cannot cross. Now, if you add some substance (sugar or salt, as before) into one compartment, the concentration in this compartment increases while the concentration in the other one stays the same. This results in a ‘difference of potential’, meaning the compartment with the higher concentration is in a state of higher energy than the other compartment – the particles ‘long for’ crossing the membrane in order to balance the concentration difference. However, while the sugar or salt particles cannot cross, water mol
