The cell membrane regulates the passage of small molecules via active and passive transport mechanisms, with endocytosis and exocytosis managing macromolecule transport. Passive transport occurs along the concentration gradient without energy, while active transport requires energy to move substances against this gradient. Endocytosis involves the uptake of materials into the cell, and exocytosis pertains to expelling materials from the cell.

1. CELL MEMBRANE
TRANSPORT

3. INTRODUCTION
• One of the main functions of the cell membrane is to regulate the passage of a variety of small
molecules across it.
• Biological membranes are semipermeable membranes through certain molecules move freely
across the membranes but the movement of the others is restricted because of size, charge or
solubility.
• There are two types of mechanisms :
1. Active Transport.
2. Passive Transport.
• Also, the transport of macromolecules across the plasma membrane is done by endocytosis and
exocytosis.

4. PASSIVE TRANSPORT (DOWNHILL MOVEMENT)
• Transport of substances is along the concentration gradient.
• It does not need energy as the substances move from region of higher concentration
to the region of lower concentration.
• Passive transport is like swimming in the direction of water flow in a river.
• There are different types of passive processes, such as
1. Simple Diffusion
2. Osmosis
3. Facilitated Diffusion

5. SIMPLE DIFFUSION
• A type of passive transport where molecules
diffuse unassisted.
• Concentration gradient results in the
movement of molecules from an area of
higher concentration to an area of lower
concentration.
• Apart from concentration gradient, kinetic
energy of molecules further fuels the
process.
• Example : passive transport of small
nonpolar molecules across the plasma
membrane.

6. OSMOSIS
• Osmosis is a specific type of diffusion; it is the passage of water from a
region of high water concentration through a semi-permeable membrane
to a region of low water concentration.

7. FACILITATED DIFFUSION
• Facilitated diffusion is the passive movement of molecules along the
concentration gradient.
• It is a selective process, i.e., the membrane allows only selective molecules
and ions to pass through it with the help of transport proteins.
• However, it prevents other molecules from passing through the
membrane.

11. ACTIVE TRANSPORT (UPHILL MOVEMENT)
• Active transport is the movement of
substances against the chemical or
electrical or gradient.
• Active transport requires energy, which is
obtained mainly by breakdown of high
energy compounds like adenosine
triphosphate(ATP).
• In fact, cells spend much of the energy
they harvest in metabolism to keep their
active transport processes running.
• Substances that are actively transported
+ +

12. SODIUM-POTASSIUM PUMP

13. TRANSPORT OF MACROMOLECULES ACROSS
THE PLASMA MEMBRANE
Endocytosis
• An active process that transports macromolecules such as proteins,
lipids, and small amounts of fluid into the cell.
• There are two types of endocytosis:
1. Pinocytosis (Cellular Drinking)
2. Phagocytosis (Cellular Eating)
• In endocytosis, the material to be internalized is surrounded by an area
of plasma membrane, which then buds off inside the cell to form a
vesicle containing the ingested material.
• The primary purpose is : Absorption of nutrients, eliminating old cells
and neutralizing pathogenic material

14. EXOCYTOSIS
• Exocytosis is the process of eliminating the material from
the cell into the external environment.
• The secretory vesicle fuses with the plasma membrane
• The primary purpose is : Eliminating cellular waste and
mode of cellular communication.