The document outlines the structure and function of cell membranes, emphasizing their role as gatekeepers that regulate material flow and maintain homeostasis. It discusses passive transport mechanisms like diffusion, facilitated diffusion, and osmosis, as well as active transport that requires energy to move substances against the concentration gradient. Additionally, it explains the concepts of hypertonic, hypotonic, and isotonic solutions, and the processes of endocytosis and exocytosis for transporting large molecules.

1. P.Syamjith M Pharm
Associate Professor
Head Department of Pharmacology
Sanjo CPS -Palakkad

2. Cell Membrane (Transport)
Cell Membrane and Cell Wall:
• ALL cells have a cell membrane made of proteins and lipids
Cell
Membrane
lipid bilayer
protein channel
protein pump
Layer 1
Layer 2
• SOME cells have cell membranes and cell walls – ex: plants, fungi
and bacteria
Cell
Membrane
Cell Wall

3. Function of the Cell Membrane:
• Cell membrane separates the components of a cell
from its environment—surrounds the cell
• “Gatekeeper” of the cell—regulates the flow of
materials into and out of cell—selectively permeable
• Cell membrane helps cells maintain homeostasis—
stable internal balance

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

7. • 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

8. DIFFUSION
Diffusion is a
PASSIVE process
which means no
energy is used to
make the
molecules move,
they have a
natural KINETIC
ENERGY

9. DIFFUSION OF LIPIDS

10. DIFFUSION THROUGH A MEMBRANE
Solute moves DOWN the concentration gradient. (HIGH
to LOW)

11. DIFFUSION
HIGH to LOW concentration

12. • 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

13. • DIFFUSION OF WATER
ACROSS A MEMBRANE
– Moves from HIGH
water concentration
to LOW water
concentration
• Water is attracted
to solutes (like salt)
so it will also travel
to areas of low
solute
concentration to
high solute
concentration.

17. • 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

20. Facilitated Diffusion
Molecules will randomly move through the pores in
Channel Proteins.

22. Types of Transport Proteins
• Channel proteins are
embedded in the cell
membrane & have a pore
for materials to cross
• Carrier proteins can
change shape to move
material from one side of
the membrane to the
other

23. Facilitated Diffusion
• Some carrier proteins do not extend through
the membrane.
– They bond and drag molecules through the lipid bilayer
and release them on the opposite side.

24. Hypertonic Solutions: contain a high concentration of solute
relative to another solution (e.g. the cell's cytoplasm). When
a cell is placed in a hypertonic solution, the water diffuses
out of the cell, causing the cell to shrivel.
Hypotonic Solutions: contain a low concentration of solute
relative to another solution (e.g. the cell's cytoplasm). When
a cell is placed in a hypotonic solution, the water diffuses
into the cell, causing the cell to swell and possibly explode.
Isotonic Solutions: contain the same concentration of solute
as another solution (e.g. the cell's cytoplasm). When a cell is
placed in an isotonic solution, the water diffuses into and
out of the cell at the same rate. The fluid that surrounds the
body cells is isotonic.

27. Active Transport
Active transport is the movement of molecules from LOW to HIGH
concentration.
Energy is required as molecules must be pumped against the
concentration gradient.
Proteins that work as pumps are called protein pumps.
Ex: Body cells must pump carbon dioxide out into the surrounding
blood vessels to be carried to the lungs for exhale. Blood vessels are
high in carbon dioxide compared to the cells, so energy is required
to move the carbon dioxide across the cell membrane from LOW to
HIGH concentration.
outside of cell
inside of cell
Carbon Dioxide
molecules

28. Active Transport
• Active Transport
– Requires energy or ATP
• Moves materials from
LOW to HIGH
concentration
•AGAINST
concentration
gradient

32. Active Transport
• Examples: Pumping Na+
(sodium ions) out and K+
(potassium ions) in—
against concentration
gradients.
–Called the
Sodium-
Potassium
Pump.

34. Sodium-Potassium Pump
• 3 Na+ pumped in for every 2 K+ pumped
out; creates a membrane potential.

35. Active Transport--Exocytosis
Exocytosis
Type of active transport
Moving things OUT
Molecules are moved out of
the cell by vesicles that fuse
the with the plasma
membrane.
This is how many hormones
are secreted and how nerve
cells communicate with
each other.

36. Food is moved into the
cell by Endocytosis
Wastes are moved out
of the cell by
Exocytosis
• Endocytosis and Exocytosis is the mechanism by which
very large molecules (such as food and wastes) get into
and out of the cell

39. Ex: White Blood Cells, which are part of the immune
system, surround and engulf bacteria by endocytosis.

41. OUT
IN
OUT IN