Passive transport is the fundamental movement of ions and other molecular substances within the cells along the concentration gradient, without any external energy. It is also known as passive diffusion.
Types Of Passive Transport
There are four types of passive transport: They are:
- Simple Diffusion: It is the movement of substances from a region of higher concentration to a lower concentration. The difference in the concentration of the two areas is termed as concentration gradient and the process of diffusion continues until this gradient neutralizes. Diffusion occurs in liquids and gases because their particles move randomly from one place to another. It is an important process in living things required for different life processes. The substances move in and out of the cells by simple diffusion.
- Facilitated Diffusion: Facilitated diffusion is the passive transportation of ions or molecules across the cell membrane through specific transmembrane integral proteins. This process does not require any cellular or external energy. Glucose transporter, ion channels, and aquaporins are some of the examples of facilitated diffusion. The cell membrane is permeable only to a few molecules that are smaller in size and non-polar. Therefore, facilitated diffusion with the help of transmembrane proteins is important.
- Filtration: Filtration is the process of separating solids from liquids and gases. The selective absorption of nutrients in the body is an example of filtration. This process does not require any energy and takes place along the concentration gradient. The kidneys are an example of a biological filter. The glomerulus filters the blood and the necessary molecules are reabsorbed. In the process of filtration, the cell membrane permits only those substances which are soluble and could easily pass through its pores.
- Osmosis: It affected by the concentration gradient and temperature. The greater the concentration gradient, the faster is the rate of osmosis. Also, the rate of osmosis increases with the increase in temperature. There is a theory of conflict about the process of osmosis. Few biologists suggest that osmosis is an active transport and not passive transport.
Examples Of Passive Transport
- Ethanol enters our body and hits the bloodstream. This happens because the ethanol molecules undergo simple diffusion and pass through the cell membrane without any external energy.
- Reabsorption of nutrients by the intestines by separating them from the solid waste and transporting the nutrients through the intestinal membrane into the bloodstream.
- When a raisin is soaked in water the water moves inside the raisin by the process of osmosis and it swells.