Difference Between Active And Passive Transport: Examples, Types

Active And Passive Transport

Active and passive transport are primary ways through which living organisms, especially at a cellular level, maintain homeostasis and ensure that the cells work properly. Active transport refers to the transport of molecules against their concentration gradient; therefore it requires energy input usually in the form of ATP. In contrast, there is no need for external energy in passive transport since it runs through spontaneous diffusion processes, whereby substances move according to their concentration gradient.

These mechanisms of transport assume an important role in cellular functions such as nutrient uptake, waste removal, and maintenance of ion gradients. This is an energy-driven mechanism essential to maintain ion and other substance concentration differences between the inside and the outside of the cell.

Types Of Active Transport

The different types of active transport are:

Primary Active Transport

• Direct use of energy in transporting the molecules against their concentration gradient.

• Uses special proteins called pumps, which pump ions across the membrane.

• Sodium-Potassium Pump: Moves 3 sodium ions out of the cell and 2 potassium ions into the cell.

• It plays a key role in maintaining both the resting membrane potential of the cell and its volume.

Secondary Active Transport

• Uses the energy derived from primary active transport to transport other substances against their gradient.

• Symport: Molecules move in the same direction; for example, glucose and sodium.

• Antiport: Molecules move in opposite directions. Example: sodium-calcium exchanger.

Bulk Transport

The details are given below:

Endocytosis

• Mechanisms by which cells engulf extracellular material.

Types

• Phagocytosis: Engulfing large particles or cells.

• Pinocytosis: Intake of liquids and small molecules.

Exocytosis

• The vesicle merges with the cell membrane and opens up to the exterior, spilling its contents.

• Vesicles carrying substances merge with the plasma membrane, spilling their content into the extracellular space.

Characteristics and Examples

• Transport in the intestine cells takes place through secondary active transport coupled with sodium ions.

• Active transport also ejects waste products from cells to maintain homeostasis.

Types Of Passive Transport

In passive transport, there is no energy requirement for the movement of molecules across the plasma membrane.

It is the movement of molecules from an area with a higher concentration to an area with a lower concentration to form an equilibrium.

Simple Diffusion

• Diffusion across a lipid bilayer from high to low concentration.

• Examples: Oxygen and carbon dioxide diffuse across respiratory membranes.

Facilitated Diffusion

• The movement of molecules across a membrane is facilitated by specific transport proteins that do not expend energy.

• Allow larger or polar molecules to pass through the membrane when they cannot diffuse directly through the lipid bilayer, e.g., glucose through GLUT transporters.

Osmosis

• A type of facilitated diffusion in which water moves through a semipermeable membrane.

• Balances the water level in the cell and the turgor pressure, which is beneficial for the functioning and stability of the cell.

Characteristics and Examples

• Facilitated diffusion is the mechanism by which nutrients like amino acids and glucose are absorbed in the intestines.

• Oxygen and carbon dioxide diffuse across alveolar membranes in the lungs, down their concentration gradients.

Table: Active vs. Passive Transport

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