Transportation is the process of movement or distribution of different materials or goods from one place to another. In general, we humans make use of different means of transportation. Similarly, living system, including plants, animals, and humans has an amazing network of the transportation system, involved in circulating food, minerals, hormones, oxygen, carbon dioxide, waste products, etc.
There are two types of transportation in our body viz. Active and Passive Transport, which help in the transportation of biochemical nutrients like water and oxygen to the cells.
Active transport: It is the biological process of movements of the molecules against the concentration gradient. Thus it requires chemical energy to transport the components from lower to higher concentrated area or body part.
Passive transport: It is the biological process of movements of the biochemical across the cell membranes and tissues without any external energy.
“Passive transport is the fundamental movements of ions and other molecular substances within the cells along the concentration gradient, without any external energy.”
There are four types of passive transport:
- Simple Diffusion
- Facilitated Diffusion
Types of Passive Transport
Diffusion is the movement of substances from a region of higher concentration to 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 liquid 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.
Also Refer: Diffusion
Facilitated diffusion is the passive transportation of ions or molecules across the cell membrane through specific transmembrane integral proteins. The molecules, which are large and insoluble require a carrier substance for their transportation through the plasma membrane. 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.
Also Read: Facilitated Diffusion
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 blood is filtered by the glomerulus 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.
In the process of osmosis, water and other molecules pass through a selectively permeable membrane in order to balance the concentration of other substances.
Osmosis is 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.
Also Read: Osmosis
Examples of Passive Transport
Following are some of the 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.
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