Diffusion is the movement of particle from outside to inside through a membrane cell of living thing, vice-versa, the movement of the particle is from an area which has a high concentration gradient to an area which has a low concentration gradient. There are three kind of diffusion first passive transport diffusion for a short passive transport diffusion or just called diffusion is same as the definition of diffusion above, second is diffusion of water across membrane or called osmosis, and the last is facilitated diffusion which need some protein channel to transfer hydrophilic particle across the hydrophobic site of membrane.
There are some understandings about each of diffusion, part of the cell, and some type of solution that make diffusion happen, below is the short definition of each part to understand diffusion:
1. Membrane cell of living things are made from glycoproteins and phospholipids. Phosphates are on the top of phospholipids membrane because it has hydrophilic trait and lipid are below of phospholipids membrane because it has hydrophobic trait.
2. Osmosis is the movement of water through a membrane from low concentration gradient to high concentration gradient. The reason that make osmosis has a force to recalcitrant the normal concentration gradient is the trait of membrane that called selective permeable.
3. Isotonic solution is the solution where the concentration of solution same as the concentration of fluid in living thing cell.
4. Hypotonic solution is the solution where the concentration of solution below the concentration inside of cell.
5. Hypertonic solution is the solution where the concentration of solution higher than concentration inside of cell.
6. Facilitated diffusion is same as normal diffusion, but sometimes there are some situation that need protein channel to transfer hydrophilic particle through a hydrophobic site of a membrane because the transfer will be so slow if the transfer doesn't through that protein. For example sugars, amino acid, ions and sometimes water.
Diffusion is the movement of particle through a membrane from hypertonic concentration to low concentration gradient, but if the concentration on the outside and inside membrane is same or called isotonic the exchange of particle still happens because there is no net exchange between particles, so the transfer of particle of diffusion doesn't need energy. Non-polar and hydrophobic material can be easily transferred into membrane because phospholipid tails as describe above are hydrophobic, for example the exchange of oxygen and carbon dioxide gasses in lung of living things use a diffusion transport because oxygen and carbon dioxide are nonpolar particle
Campbell et al.2008.Biology Concepts & Connection Sixth Edition. United States