Question

The type of diffusion in which substances move across the membrane along their concentration gradient in the presence of certain or transport proteins is called as
A) Simple diffusion
B) Facilitated diffusion
C) Osmosis
D) Active transport

Answer 1

Hint: Diffusion is a process in which molecules move from a region of higher concentration to a region of lower concentration. There is no expenditure of energy.

Complete Answer:
A) Simple diffusion: Simple diffusion is a process in which the molecules move through a semipermeable membrane from a region of higher concentration to a region of lower concentration without the help of any transport protein.
- It occurs without the expenditure of energy.
- Example – movement of oxygen through the cell membrane into each cell.

B) Facilitated diffusion: It is a process in which molecules move through a semipermeable membrane from a region of higher concentration to a region of lower concentration with the help of transport proteins.
- It also occurs without the expenditure of energy.
- Example- Movement of glucose molecules across a cell membrane.

C) Osmosis: It is a process in which solvent moves from a region of higher solvent concentration to a region of lower concentration gradient through a semi- permeable membrane.
- Example – movement of water inside the cell.

D) Active transport: It is a process in which movement of molecules takes place against the concentration gradient i.e. from a region of lower concentration to the region of higher concentration through a semipermeable membrane.
- It occurs with the help of energy i.e. ATP.
- Example- movement of glucose into the intestinal wall of humans.

Name of processes	Direction of movement	Expenditure of energy	Carrier proteins required required	Examples
Simple diffusion	From a region of higher concentration to a region of lower concentration	No expenditure of energy takes place.	No carrier proteins required.	Gases and liquids
Facilitated diffusion	From a region of higher concentration to a region of lower concentration	No expenditure of energy takes place.	Carrier proteins required.	Glucose
Osmosis	From a region of higher concentration to a region of lower concentration	No expenditure of energy takes place.	No carrier proteins required.	Water only
Active transport	From a region of lower concentration to a region of higher concentration	Expenditure of energy takes place.	carrier proteins and ATP energy required.	Ions, sugars, amino acids etc.

Therefore, the correct answer is option B.
Note: In case of facilitated diffusion there is no use of energy I.e. ATP. Also the proteins act as a carrier for the movement.