Question

The cellular transport method which involves use of transmembrane proteins without energy expenditure is called

• A. diffusion
• B. facilitated diffusion
• C. active transport
• D. exocytosis

Answer 1

Answer: (B)

The diffusion of hydrophilic substances along the concentration gradient downhill transport through fixed membrane transport protein without involving energy expenditure, is called facilitated diffusion. This diffusion is highly specific as it allows cell to select substances for uptake. Two major types of transport proteins viz. carrier proteins and channel proteins are required for facilitated diffusion. Diffusion is the process of movement of particles from the region of higher concentration to the region of lower concentration. It does not require any special membrane proteins or expenditure of energy. Active transport is the movement of particles against their concentration gradient (uphill transport), which involves the use of Special membrane proteins as well as the expenditure of energy in the form of $ATP$. Exocytosis is a type of bulk transport in which materials are exported A-out of the cell via secretory vesicles. It involves energy expenditure in the form of $ATP$ but does not make use of transport proteins.