Passive Transport

Passive transport is one of the techniques used for transportation in plants and animals. Transport usually occurs in two forms- Active transport and Passive transport. Active transport helps in the uphill movement of substances. On the other hand, passive transport helps in the downward movement of substances. There are four types of passive transport- diffusion, facilitated diffusion, osmosis, and filtration. In this article, we will study the definition of passive transport, types of passive transport, diagram, of passive transport, examples of passive transport, the difference between active transport and passive transport, and the importance of active transport.

Definition of Passive Transport

Passive transport is the process by which molecules are transported from one place to another along a concentration gradient. It does not require energy but sometimes carrier molecules assist in the movement process.

E.g If we spray a bottle of perfume at a single point, after a while the adjoining area also starts to smell like the perfume. This happens due to the movement of air molecules from a region of high concentration to a region of lower concentration.

What is Passive Transport?

Passive transport is the opposite of active transport. Cells move materials across a body through cell walls and cell membranes. The transport process is mainly of two types- Active transport and Passive Transport. Passive transport does not require any energy, the molecules just roll with the flow. Passive transport aids in the movement of nutrients like amino acids and glucose across an organism’s body.

In Active Transport, energy is needed to move molecules from one area to another. In active transport, molecules move from a region of low concentration to a high concentration with the help of the energy quotient, known as ATP. E.g. Nerve impulses are transmitted across the nervous system with the help of ATP.

Types of Passive Transport

Passive transport is mainly categorised into four types based on how the molecules move across a membrane. These are:

Simple Diffusion

In simple diffusion, molecules move on their own without any support along the concentration gradient. Particles move from a highly crowded region to a less crowded area. This movement occurs till the point an equilibrium is established. E.g. The exchange of oxygen and carbon dioxide in the lungs occurs with the help of diffusion.

Facilitated Diffusion

Facilitated diffusion is defined as the substances moving through the semi-permeable membrane from a region of higher concentration to a region of lower concentration with the help of transport proteins. These proteins form channels or carriers to allow the passage of the molecules. This movement is faster as compared to simple diffusion. E.g The movement of water molecules through the body occurs with the help of channel proteins known as aquaporins.

Osmosis

Osmosis is a type of facilitated diffusion that happens on the basis of water potential. In this, water moves from a region of low solute concentration to a region of high solute concentration across a semi-permeable membrane. The semi-permeable is selective in nature and allows only specific molecules to pass through it and blocks the others. Osmosis can be further divided into two types based on the direction of the movement of water. If the water moves towards the inside of the cell, the process is known as Endosmosis. If the water moves outside the cell, then the process is known as Exosmosis.

Filtration

Filtration involves the process of separation of solids from liquids and gases. This also does not involve the use of energy and works according to the concentration gradient. The membrane utilised for this process is selective in nature which allows soluble substances to pass through and stops the other molecules. E.g. In humans, the kidneys are responsible for the filtration process. The kidneys allow the body to absorb useful nutrients and water and the rest of waste material is excreted from the body.

Diagram of Passive Transport

Below is a diagram depicting the various types of passive transport:

Examples of Passive Transport

Some examples of Passive transport are:

• Water gets transported from the root to the upper parts of the plant through capillary action that is based on passive transport. The adhesive force of water works according to the concentration gradient.
• People who have damaged kidneys undergo dialysis. The dialysis machine helps the body to filter waste material and absorb useful nutrients.
• Fermentation process is used for making food products like yoghurt and bread. The bacterial membrane allows sugar molecules to enter through specific protein channels and lactic acid to exit. This utilizes the process of facilitated diffusion.
• The lungs help in the process of respiration by infusing the blood with oxygen and removing carbon dioxide. The lining of the alveoli helps oxygen to be diffused passively.
• Osmosis helps the plants to absorb minerals like nitrogen and phosphorus from the soil.

Active Transport vs. Passive Transport

As we know, transport is of two types- Active and Passive. Active transport uses ATP whereas passive transport does not. Active transport requires oxygen to operate whereas passive transport does not need oxygen. Active Transport is a type of transport system which requires energy to transport large molecules like protein, sugar etc. from lower concentration to higher concentration.

Importance of Passive Transport

Following points highlight the importance of passive transport:

FAQ’s – Passive Transport

1. What is the Difference between Active and Passive Transport?

The difference between active and passive transport is that active transport uses ATP to move molecules, whereas passive transport occurs on the basis of concentration gradient.

2. What is the Difference between Passive and Facilitated Diffusion?

Facilitated diffusion is a type of passive transport in which the molecules get transported across the concentration gradient with the help of carrier molecules.

3. Is passive Diffusion the same as Simple Diffusion?

Yes, passive diffusion is the same as simple diffusion. In simple diffusion, molecules move from a region of higher concentration to lower concentration.

4. Which method of Simple Transport is also known as Passive Diffusion?

Plasma membrane transport is also known as passive diffusion. The molecules move across the membranes based on their concentration gradient. In case of plasma membrane, the membrane is selectively permeable.

5. What is an Example of one Process that is a Type of Passive Transport?

The excretion carried out by the kidneys occurs through filtration, which is a type of passive transport. In filtration, the solid molecules are separated from the liquid and gas molecules.