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A cell membrane regulates, which substances can enter and leave the cell based on their size and polarity.
Ions cross the cell membrane through which of the following processes?
a) Simple diffusion
b) Active transport
c) Endocytosis
d) Osmosis
e) Facilitated diffusion

Last updated date: 20th Jun 2024
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Hint:-The cell membrane is mainly made up of phospholipids in a consecutive manner (a “bilayer”). In cell membranes, only small and nonpolar materials can move through the lipid bilayer.
All substances that move through the membrane, by either of the two methods, which are categorized based on the requirement of energy - ACTIVE & PASSIVE.

Complete answer:
Option a) Simple diffusion is the movement of particles from an area of greater or higher concentration to a region of lower concentration due to their own intrinsic kinetic energy. Simply put, it is a passive movement of molecules along their concentration gradient. If the particles are too small, simple diffusion can happen across cell membranes.
This option is incorrect.
Option b) In Active transport, molecules are carried from a region of lower concentration to a region of higher concentration against the concentration gradient with the utilisation of ATP. It uses ATP to provide energy to the proteins providing the transport.
This option is incorrect.
Option c) Endocytosis is a process in which there is inundation of material by the cell membranes’ invagination. It is a cellular process, in which the substances are carried into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a sac or vesicle, which contains the ingested material.
This option is incorrect.
Option d) Osmosis is the diffusion of water molecules through a semipermeable or a differentially permeable membrane along the concentration gradient. The cause of shifting of solvent molecules, is the concentration difference of solutes in the solutions.
This option is incorrect.
Option e) Facilitated diffusion is the passive movement of molecules along their concentration gradient with the help of membrane proteins known as channel proteins or carrier proteins.
It is called facilitated diffusion because the ions move across the cell membrane with the help of membrane proteins.
Thus, this is the correct option.

- Facilitated diffusion is also called - passive-mediated transport or facilitated transport.
- It does not directly require chemical energy from ATP hydrolysis, because facilitated transport is a passive process.
- The molecules and ions move down their concentration gradient, thus representing its diffusive nature.