Evidences of diffusion in plants

Answer 1

in mammals, where there is a synapse, a chemical is diffused across the gap between the neurones. :)

Answer 2

Diffiusion is the very natural movement of things (usually gasses or substances in solution, but really anything) from an area of higher concentration to an area of lower concentration. Most of what a plant does is through diffusion. For that matter, most of what goes on in your body or any organism's body is through diffusion.

Plants absorb water and nutrients from the soil into their roots by allowing the nutrients and water to diffuse from an area of higher concentration (recently watered rich soil) to an area of lower concentration (a plant that needs more water and nutrients). When a plant is not watered, it will dry up along with the soil. However, if a plant is overwatered, it will get droopy and wet-looking because, like the soil it is planted in, it will have a lot of water in it. Respiration in a plant is also by diffusion.

Really though, you work by diffusion too. There is more oxygen in the air than in your blood, so when you pull air into your lungs, which are basically just a two-cell-thick bag of air surrounded by blood vessels, the oxygen goes from the air (high concentraion) into your blood (low concentration); the reverse happens with carbon dioxide. When you eat, various enzymes break down food into tiny particles, usually just one molecule, which are then absorbed into your blood in the intestines for use by your body through a similar means as oxygen in the lungs: there is more sugar or amino or fatty acid in the food than in your blood, so it moves from an area of higher concentration to an area of lower concentration. Even getting drunk: the alcohol in beer (~5% alcohol) moves into your blood, which has a much lower concentration of alcohol (hopefully not much more than .5% or so).