What are the differences between diffusion and active transport?

“Active transport is the movement of molecules across a membrane from a region of lower concentration to a region of higher concentration against the concentration gradient, often assisted by enzymes and requires energy”
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Difference Between Active And Passive Transport
Active Transport
Passive Transport
Key Points on Active and Passive Transport

“Passive transport is the movement of ions and molecules across the cell membrane without requiring energy.”

Active and passive transport are the two main biological processes that play a crucial role in supplying nutrients, oxygen, water and other essential molecules to the cells along with the elimination of waste products. In essence, active and passive transport work for the same goals/ purposes, but with different movement.

Let us see how active and passive transport are different from each other.

Difference Between Active And Passive Transport

Following are the important difference between active and passive transport:

Active Transport	Passive Transport
Requires cellular energy.	Does not require cellular energy.
It circulates from a region of lower concentration to a region of higher concentration	It circulates from a region of higher concentration to a region of lower concentration
Required for the transportation of all the molecules such as proteins, large cells, complex sugars, ions, etc.	Required for the transportation of all soluble molecules, including oxygen, water, carbon dioxide, lipids, sex hormones, etc.
It transports various molecules in the cell.	It is involved in the maintenance of the equilibrium level inside the cell.
Active transport is a dynamic process.	Passive Transport is a physical process.
It is highly selective.	It is partly non-selective
Active transport is a rapid process.	Passive transport is a comparatively slow process.
Transpires in one direction.	Transpires bidirectionally.
Active transportation is influenced by temperature.	Passive transportation is not influenced by temperature.
In active transport, carrier proteins are required	In passive transport, carrier proteins are not required
This process reduces or halts as the oxygen content level is reduced.	This process is not affected by the level of oxygen content.
Metabolic inhibitors can influence and stop active transport.	Passive transportation is not influenced by metabolic inhibitors.
Different types of Active Transport are – Exocytosis, endocytosis, sodium-potassium pump	Different types of Passive Transport are – Osmosis, diffusion, and facilitated diffusion

Active Transport

This is the biological process in which molecules move against the concentration gradient and require chemical energy to move biochemical compounds from a lower region to the high region. Therefore, this process uses ATP – Adenosine triphosphate to pump molecules through a concentration gradient. Complex sugar, ions, large cells, proteins and other particles are transported in this process. There are two types of Active transport:

Primary Active transport
Secondary Active transport

Exocytosis, endocytosis and sodium-potassium pump are a few examples of active transport. The process of endocytosis and exocytosis are utilized by all the cells for transportation of molecules which cannot passively permeate via the membrane.

Endocytosis is the process of active transportation of molecules into the cells by the action of engulfing it along with its membrane.
Exocytosis produces a counter function thereby forcing molecules out of the cell. The process of homeostasis facilitates an equal flow of molecules in and out of a cell which confers that the number of molecules that enter the cell through endocytosis equates to the number of molecules that exits a cell through the process of exocytosis. Both the processes assure that nutrients and wastes are balanced for the smooth functioning of the cells.

Main Article: Active Transport.

Passive Transport

In this biological process, energy is not required for transporting the molecules, as the biochemicals move from a region of higher concentration to a region of lower concentration. All particles which are easily soluble are transported through passive transport. This process is carried out to maintain the balance and the equilibrium level in a cell. All the waste molecules including, water and carbon dioxide is separated and moved out of the cell using passive transport. Meanwhile, nutrients like oxygen that are functional for the cell are diffused in this process. Osmosis, diffusion and facilitated diffusion are some of the examples of passive transport.

Main Article: Passive Transport

Key Points on Active and Passive Transport

Active transport requires energy for the movement of molecules whereas passive transport does not require energy for the movement of molecules.
In active transport, the molecules move against the concentration gradient whereas in passive transport, the molecules move along the concentration gradient.
Uptake of glucose in the human intestine works on the principle of active transport.
Simple diffusion, facilitated diffusion, osmosis and filtration are examples of passive transport.

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Related Links:

Diffusion
Transportation In Plants
Facilitated Diffusion

Active transport moves molecules and ions from lower concentration to higher concentration with the help of energy in the form of ATP. On the other hand, passive transport moves molecules and ions from a higher concentration to lower concentration without any energy.

ATP hydrolysis provides energy for the movement of molecules and ions across a concentration gradient. The movement of molecules occurs either inside the cells (endocytosis) or out of the cells (exocytosis).

Examples of active transport include sodium-potassium pump, uptake of mineral ions by the roots of the plants, etc. Whereas, the examples of passive transport include the exchange of gases in the alveoli of the lungs and the exchange of nutrients in the kidneys.

Active and passive transport regulate the entry and exit of ions and molecules in a cell. These processes allow only specific materials to cross spontaneously through the cell membrane. Rest need a carrier to pass through the membrane.

Passive transport can be of the following different types:

Simple diffusion
Osmosis
Facilitated diffusion

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Living cells need to take up raw materials and nutrients to carry out complex biochemical reactions. At the same time, waste products need to be disposed of in the cell to prevent toxicity to the living cells. These substances move in and out of the cells by different transport processes such as diffusion, osmosis and active transport, which occur through the cell plasma membrane. The semi-permeable cell membrane and the properties of the substances determine whether diffusion, osmosis, or active transport is involved in the movement of different substances across the cell plasma membrane.

To identify the differences between these three transport processes, consider (1) what are the substances involved, (2) how do these substances move, and (3) whether energy is required in and for each of these processes. This 3 minute-read will provide you with the quick revision you need on the what’s and how’s that spell out the differences between diffusion, osmosis, and active transport.

What is Diffusion, Osmosis and Active Transport?

Diffusion is the movement of a substance down a concentration gradient. Diffusion can happen with or without passing through a semi-permeable membrane (cell plasma membrane is semi-permeable).
Osmosis is the diffusion of water molecules down a concentration gradient through a semi-permeable membrane.
Active transport is the movement of a substance against a concentration gradient.

What are the Substances Involved?

Examples of substances transported by diffusion across the cell plasma membrane are gases such as oxygen and carbon dioxide, glucose, and urea.
Osmosis refers specifically to the movement of water molecules across a semi-permeable membrane.
Active transport involves substances such as mineral ions (uptake by plant root) and glucose (taken up in the small intestine).

How do the Substances Move?

In diffusion, the substance moves down the concentration gradient, from high to low concentration (from a region of high substance concentration to a region with low substance concentration).

Water molecules in osmosis also move down the concentration gradient (from a region where water molecules are high in concentration, to a region with low concentration of water molecules) through a semi-permeable membrane. The concentration of water molecules is high in a diluted solution while the water concentration is low in concentrated solutions. In other words, during osmosis, water molecules move from a diluted solution to a high concentration solution.

Both diffusion and osmosis act to balance the concentration of substances in a solution.

In active transport, the substance moves against the concentration gradient (from a region where the substance concentration is low to a region with a high concentration of the substance).

Do All these Processes Require Energy?

Broadly speaking, transport across plasma membrane can be passive or active in terms of energy requirement. Passive transport does not require energy while active transport needs energy to take place.

Both diffusion and osmosis do not require energy because the substances move down the concentration gradient, from high to low concentration. The net flow of the substances is caused by random movement of the substances owing to the energy level of the substances.

However, active transport requires energy as the substances involved move against the concentration gradient, from low to high concentration. This energy is derived from ATP (adenosine triphosphate), energy-rich molecules in living cells.

Summary Table: Differences between Diffusion, Osmosis, and Active Transport