This document discusses passive transport mechanisms in cell membranes. It defines passive transport as the movement of molecules or ions across the cell membrane without requiring energy. There are three main types of passive transport: diffusion, facilitated diffusion, and osmosis. Diffusion is the random movement of molecules from an area of higher concentration to lower concentration. Facilitated diffusion uses carrier proteins to transport molecules across the membrane. Osmosis is the diffusion of water across the membrane, moving from an area of lower solute concentration to higher concentration.

1. This content is only for education purpose
Dr. Poonam Bansal
Assistant Professor
Maharishi Markandeshwar (Deemed to Be University)
Mullana
PASSIVE TRANSPORT

2.  Cell membrane is also called as plasma
membrane.
 Separates the interior of the cell to the outside
environment
 Consist of lipid bilayer
 It is selectively permeable.
 Regulates the transport of mineral ions in and
out of the cell
Cell Membrane

3. Transport across Cell Membrane
Passive Transport Active Transport
Doesn't use energy Cells does uses energy
Is of three types: Is of two types:
a) Diffusion a) Primary
b) Facilitated Diffusion b) Secondary
c) Osmosis

4. Passive Transport
 It does not require expenditure of metabolic energy.
 Molecules or ions move from an area of higher concentration to area of lower
concentration.
 Molecules move randomly.

5. Diffusion
 Diffusion is the process of movement
of molecules under a concentration
gradient.
 Diffusion helps in the movement of
substances in and out of the cells.
 The molecules move from a region of
higher concentration to a region of
lower concentration until the
equilibrium is achieved.

6. Facilitated Diffusion
 Facilitated diffusion is a passive movement of
molecules across the cell membrane from the
region of higher concentration to the region of
lower concentration by means of a carrier
molecule.
 Carrier Proteins are specific – they select
only certain molecules to cross the membrane
 Transports larger or charged molecules
 Examples: transport of glucose, amino acids,
galactose, etc. in the peripheral cells

7. Factors affecting Facilitated Diffusion
1. Temperature
Temperature increases the movement of the molecules increases due to an increase in energy.
2. Concentration
The movement of the molecules takes place from the region of higher concentration to lower concentration.
3. Diffusion Distance
The diffusion rate is faster through smaller distance than through the larger distance. For eg., gas diffuses much
faster through a thin wall than through a thick wall.
4. Size of the molecules
The smaller molecules are lighter and hence diffuse faster than the larger molecules.

8. Osmosis
It is the movement of solvent
molecules from the region of lower
concentration to the region of higher
concentration through a
semipermeable membrane.

9. Osmotic Solution
1. Isotonic solution
one that has the same concentration of solutes both
inside and outside the cell.
2. Hypertonic solution
one that has a higher solute concentration outside the
cell than inside.
3. Hypotonic solution
one that has a higher solute concentration inside the
cell than outside.

10. Types of Osmosis
•Endosmosis
When a substance is placed in a hypotonic
solution, the solvent molecules move inside the
cell and the cell becomes turgid or undergoes
deplasmolysis. This is known as endosmosis.
•Exosmosis
When a substance is placed in a hypertonic
solution, the solvent molecules move outside
the cell and the cell becomes flaccid or
undergoes plasmolysis. This is known as
exosmosis.

11. Difference between Diffusion and Osmosis
Parameters Osmosis Diffusion
Type of substance
solvent can move from a
region of lower concentration
to higher concentration.
Any type of substance can move
from an area of higher
concentration to lower
concentration.
Semi-permeable
membrane
It requires a semi-permeable
membrane.
It has no need of a semi-permeable
membrane.
Medium
It takes place only in a liquid
medium.
It takes place in any medium-
solid, liquid, or gas.
Concentration
The solvent’s concentration
does not become equal on
both of the membrane sides.
The diffusion substance’s
concentration equalizes to fill the
space available.