Active and Passive Transport

Active Transport
Passive Transport

Active and passive transport are biological processes that move oxygen, water and nutrients into cells and remove waste products. Active transport requires chemical energy because it is the movement of biochemicals from areas of lower concentration to areas of higher concentration. On the other hand, passive trasport moves biochemicals from areas of high concentration to areas of low concentration; so it does not require energy.

Comparison chart

Active Transport

Passive Transport

Definition Active Transport uses ATP to pump molecules AGAINST/UP the concentration gradient. Transport occurs from a low concentration of solute to high concentration of solute. Requires cellular energy. Movement of molecules DOWN the concentration gradient. It goes from high to low concentration, in order to maintain equilibrium in the cells. Does not require cellular energy.
Types of Transport Endocytosis, cell membrane/sodium-potassium pump & exocytosis Diffusion, facilitated diffusion, and osmosis.
Types of Particles Transported proteins, ions, large cells, complex sugars. Anything soluble (meaning able to dissolve) in lipids, small monosaccharides, water, oxygen, carbon dioxide, sex hormones, etc.
Examples phagocytosis, pinocytosis, sodium/potassium pump, secretion of a substance into the bloodstream (process is opposite of phagocytosis & pinocytosis) diffusion, osmosis, and facilitated diffusion.
Importance In eukaryotic cells, amino acids, sugars and lipids need to enter the cell by protein pumps, which require active transport.These items either cannot diffuse or diffuse too slowly for survival. It maintains equilibrium in the cell. Wastes (carbon dioxide, water, etc.) diffuse out and are excreted; nutrients and oxygen diffuse in to be used by the cell.
Functions Transports molecules through the cell membrane against the concentration gradient so more of the substance is inside the cell (i.e. a nutrient) or outside the cell (i.e. a waste) than normal. Disrupts equilibrium established by diffusion. Maintains dynamic equilibrium of water, gases, nutrients, wastes, etc. between cells and extracellular fluid; allows for small nutrients and gases to enter/exit. No NET diffusion/osmosis after equilibrium is established.

Contents: Active and Passive Transport

Process

There are two types of active transport: primary and secondary. In primary active transport, specialized trans-membrane proteins recognize the presence of a substance that needs to be transported and serve as pumps, powered by the chemical energy ATP, to carry the desired biochemicals across. In secondary active transport, pore-forming proteins form channels in the cell membrane and force the biochemicals across using an electromagnetic gradient. Often, this energy is gained by simultaneously moving another substance down the concentration gradient.

Example of primary active transport, where energy from hydrolysis of ATP is directly coupled to the movement of a specific substance across a membrane independent of any other species.
Example of primary active transport, where energy from hydrolysis of ATP is directly coupled to the movement of a specific substance across a membrane independent of any other species.

There are four main types of passive transport: osmosis, diffusion, facilitated diffusion and filtration. Diffusion is the simple movement of particles through a permeable membrane down a concentration gradient (from a more concentrated solution to a less concentrated solution) until the two solutions are of equal concentration. Facilitated diffusion uses special transport proteins to achieve the same effect. Filtration is the movement of water and solute molecules down the concentration gradient, e.g. in the kidneys, and osmosis is the diffusion of water molecules across a selectively permeable membrane. None of these processes require energy.

Three different mechanisms for passive transport in bilayer membranes. Left: ion channel (through a defined trajectory); center: ionophore/carrier (the transporter physical diffuses through with the ion); right: detergent (non-specific membrane disruption).
Three different mechanisms for passive transport in bilayer membranes. Left: ion channel (through a defined trajectory); center: ionophore/carrier (the transporter physical diffuses through with the ion); right: detergent (non-specific membrane disruption).

Video explaining the differences

Here's a good video explaining the process of active and passive transport:

Examples

Examples of active transport include a sodium pump, glucose selection in the intestines, and the uptake of mineral ions by plant roots.

Passive transport occurs in the kidneys and the liver, and in the alveoli of the lungs when they exchange oxygen and carbon dioxide.

References

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