Some ion channels control the amount of ions going in and out of the cells by having gates that can open and close. Other functions of the proteins include providing receptor sites for hormonal binding, pumping energy to move water-soluble molecules and ions and enzymes that can help to speed up the chemical reactions happening around the membrane.
Concentration Gradient.
Before getting into the types of transport across a cell, it is important to know about the concentration gradient. A concentration gradient is the movement of molecules from an area of higher number of particles to a lower number of particles until they are evenly distributed (Study.Com 2003).
1) Diffusion.
Firstly, Diffusion is the movement particles from higher concentration to a lower concentration. We can experience diffusion in our everyday life. From the way the scent of your perfume spreads all around the room to the diffusing of the sugar in your tea. However the most important examples of diffusion occurs in our body. This process occurs throughout our body and without it cells and body tissues cannot get important nutrients that are essential for our survival. .
Lungs.
The human lungs approximately have 300 million alveoli in each lung. Alveoli is the tiny air sacs in the lungs that are only one cell thick. (Simmons n.d) Our lungs are made in a way that can maximize the surface area to increase gas diffusion. When the blood arriving at the alveoli has a higher concentration of Carbon Dioxide, (as a result of respiration by the body cells) than the alveoli, the carbon dioxide diffuses out of the blood and into the alveolar air. Likewise, when the air in the alveoli has a higher concentration of Oxygen, they move into the blood capillaries by diffusion and combine with the hemoglobin in the red blood cells to form oxyhemoglobin. (Gaseous Exchange in Lungs 2013).
2) Osmosis.
Another form of transport between the cells is Osmosis.