Facilitated diffusion is performed by various types of proteins that are embedded within the cell membrane. While there are hundreds of different proteins throughout the cell, only two types are found associated with facilitated diffusion: channel proteins and carrier proteins.

Which of the following is an example of facilitated diffusion? water moves out of the cell passing through channel proteins in the cell membrane.

Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins.

passive transport

The net flow of molecules by facilitated diffusion, through either carrier proteins or channel proteins, is always energetically downhill in the direction determined by electrochemical gradients across the membrane. In many cases, however, the cell must transport molecules against their concentration gradients.

The carrier proteins involved in facilitated diffusion simply provide hydrophilic molecules with a way to move down an existing concentration gradient (rather than acting as pumps). Channel and carrier proteins transport material at different rates.

Facilitated diffusion is diffusion along transport proteins. It is passive. Examples are aquaporins and neurotransmitters.

Channel proteins

For example, GLUT1 is a named carrier protein found in almost all animal cell membranes that transports glucose across the bilayer. Other specific carrier proteins also help the body function in important ways. Cytochromes operate in the electron transport chain as carrier proteins for electrons.

Active transport is not the same as facilitated diffusion. Both active transport and facilitated diffusion do use proteins to assist in transport. However, active transport works against the concentration gradient, moving substances from areas of low concentration to areas of high concentration.

Active transport is usually associated with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants.

During active transport, a protein pump uses energy, in the form of ATP, to move molecules from an area of low concentration to an area of high concentration. An example of active transport is the sodium-potassium pump, which moves sodium ions to the outside of the cell and potassium ions to the inside of the cell.

Substances that can move via bulk transport are like hormones, polysaccharides, etc. An example of this is the engulfing of pathogens by phagocytes (endocytosis), then the release of the hydrolysed pieces of the pathogen outside the cell by exocytosis.

Endocytosis vs exocytosis: a comparison

Some examples of cells using exocytosis include: the secretion of proteins like enzymes, peptide hormones and antibodies from different cells, the flipping of the plasma membrane, the placement of integral membrane proteins(IMPs) or proteins that are attached biologically to the cell, and the recycling of plasma …

Vesicles or other bodies in the cytoplasm move macromolecules or large particles across the plasma membrane. There are two types of vesicle transport, endocytosis and exocytosis (illustrated in the Figure below). Both processes are active transport processes, requiring energy.

Facilitated diffusion takes place due to a difference in concentration on both sides of the membrane, in the direction of the lowest concentration, and does not require energy.

Endocytosis is the process of actively transporting molecules into the cell by engulfing it with its membrane. They sort the received molecules into the other components in the pathway through trans vesicular compartments such as endosomal carrier vesicles or multivesicular bodies. …

Pinocytosis

Golgi apparatus. Golgi apparatus. The stacks of flattened membranous vesicles are called Golgi apparatus. It basically stores, packs and modifies the products in vesicles. It temporarily stores protein that moves out of the cell through the vesicles of the Golgi apparatus.

The Golgi apparatus is a series of membranes shaped like pancakes. The single membrane is similar to the cell membrane in that it has two layers. Because the Golgi complex absorbs vesicles from the rough ER, you will also find ribosomes in those pancake stacks.