Similarities Between Active Transport and Facilitated Diffusion

Active transport and facilitated diffusion are two ways of transport of ions and molecules through the cell membrane, executed through a membrane carrier.

What is Active Transport?

The movement of ions and molecules across a cell membrane, from a region with a lower concentration to a region with higher concentration is called active transport. It is executed against an obstructing factor (usually – a concentration gradient) and requires energy.

The active transport is related to the accumulation of high concentrations of different substances that the cell needs: ions, amino acids, glucose, etc. It is always done by carriers – proteins embedded in the cell membrane. The carriers in the active transport are called pumps. The speed at which they work may change. For example, when the ions are in concentrations, normal for the body, the operating speed of the ion pumps is approximately half its maximum speed.

In order to move molecules against a gradient, polar repulsion, or another obstructing factor the active transport uses energy. Depending on the source of energy used for the active transport, it is divided into two types:

• primary active transport,
• secondary active transport.

Primary active transport uses the energy of adenosine triphosphate (ATP), which degrades to adenosine diphosphate (ADP) and phosphate and releases energy.

Secondary active transport uses the energy of the electrochemical gradients instead of the chemical energy of ATP. In order to have a secondary active transport, it is necessary to have a primary one, to create gradients.

Example of active transport is the mineral ions uptake into plant roots. The plants need mineral salts from the soil for their development. The salts’ concentrations in the soil solution are very limited. Active transport enables root cells to extract the necessary minerals from the dilute solution against the concentration gradient.

What is Facilitated Diffusion?

Opposed to the active transport, the facilitated diffusion is a spontaneous process of passive transportation of ions or molecules across a biological membrane. It is carried out along concentration or electrochemical gradient and the process does not require energy from adenosine triphosphate. A membrane carrier is used for the transported substance. The carriers (as in the active transport) are proteins embedded in the cell membrane. The facilitated diffusion is faster than simple diffusion, but as the concentration of the transported substance increases, the carrier is saturated and the rate of facilitated diffusion stops increasing. The ions or molecules are transported with the carrier. The carrier undergoes spontaneous conformational changes of its molecule, during which the transported ion or molecule binds to the carrier at the higher concentration side of the membrane and is released on its other side.

Example for facilitated diffusion is the transport of glucose, chloride ions, and sodium ions. The lipid layer of the cell membrane is impermeable for them, so their transport needs to be facilitated. The carriers (proteins) span the cell membrane and provide an entrance for those ions and molecules.

Similarities Between Active Transport and Facilitated Diffusion

1. Active transport and facilitated diffusion are two ways of transport of ions and molecules through the cell membrane.
2. Both active transport and facilitated diffusion are executed through a membrane carrier (protein).
3. The active transport and facilitated diffusion share the same goal – to ensure the transport of substances across the cell membrane.
4. The speed of the active transport and facilitated diffusion depends on the concentration of the transported substance in the cell.

Summary:

• Active transport and facilitated diffusion are two ways of transport of ions and molecules through the cell membrane, executed through a membrane carrier.

• The movement of molecules across a cell membrane, from a region with a lower concentration to a region with higher concentration is called active transport. It is executed against a concentration gradient and requires energy.
• The facilitated diffusion is a spontaneous process of passive transportation of ions or molecules across a biological membrane, carried out along a concentration gradient and not requiring energy.

• The speed of the active transport and facilitated diffusion depends on the concentration of the transported substance in the cell.

• Example of active transport is the mineral ions uptake into plant roots; example for facilitated diffusion is the transport of glucose, chloride ions, and sodium ions.