This document summarizes membrane transport mechanisms in cells. It describes passive transport mechanisms like diffusion, facilitated diffusion, and osmosis which move molecules down concentration gradients without requiring energy. Active transport mechanisms like ion pumps use ATP energy to move molecules against concentration gradients. Passive transport includes the movement of oxygen, glucose, and water across membranes. Active transport examples provided are ion transport across membranes and vesicle trafficking processes in cells like exocytosis.

1. Membrane transport
by
E.ANANTHARAJ,1st msc ,cas in botany
University of madras
Introduction;
The plasma membrane is a selectively permeable barrier
between the cell and the extracellular environment.
Its permeability properties ensure that
essential molecules such as ions, glucose, amino acids, and
lipids readily enter the cell, metabolic intermediates remain
in the cell, and waste compounds leave the cell.
Movement of
virtually all molecules and ions across cellular membranes
is mediated by selective membrane transport proteins embedded
in the phospholipid bilayer.

2. Passive transport

3. Passive Transport
A process that does not require energy to move
molecules from a HIGH to LOW concentration
 Diffusion
 Facilitated Diffusion
 Osmosis

4. • Diffusion is the movement of small particles across a
selectively permeable membrane like the cell membrane
until equilibrium is reached.
These particles move from an area of high concentration
to an area of low concentration.
outside of cell
inside of cell

5. • Facilitated Diffusion is the movement of larger
molecules like glucose through the cell membrane –
larger molecules must be “helped”
Proteins in the cell membrane form channels for large
molecules to pass through
Proteins that form channels (pores) are called protein
channels
outside of cell
inside of cell
Glucose molecules

6. • Osmosis is the diffusion of water through a selectively
permeable membrane like the cell membrane
Water diffuses across a membrane from an area of high
concentration to an area of low concentration.
Semi-permeable
membrane is
permeable to water,
but not to sugar

7. Active Transport
• Cells may need to move molecules against concentration
gradient
– shape change transports solute from
one side of membrane to other
– protein “pump”
conformational change
– “costs” energy = ATP
low
ATP
high
“The Doorman”

8. Active transport
• Many models & mechanisms
ATP
ATP
antiport
symport

9. summery
Passive Transport
Process
Energy Source
Example
Simple diffusion
Kinetic energy
Movement of O2 through
membrane
Facilitated
diffusion
Kinetic energy
Movement of glucose into cells
Osmosis
Kinetic energy
Movement of H2O in & out of
cells
Filtration
Hydrostatic
pressure
Formation of kidney filtrate

10. Active Transport
Process
Energy Source
Example
Active transport of solutes
ATP
Movement of ions across
membranes
Exocytosis
ATP
Neurotransmitter secretion
Endocytosis
ATP
White blood cell phagocytosis
Fluid-phase endocytosis
ATP
Absorption by intestinal cells
Receptor-mediated
endocytosis
ATP
Hormone and cholesterol
uptake
Endocytosis via caveoli
ATP
Cholesterol regulation
Endocytosis via coatomer
vesicles
ATP
Intracellular trafficking of
molecules

11. REFERENCES
Books ;
.1.Molecular cell biology 5th edition .Lodish et.al
2.p.s verma &v.k agarwal
Online source;
1,www.biology junction.com
2,www.uma.maine.edu
3,www.ocuy.org.