2. Passive transport
The movement of molecules across the plasma
membrane from an area of high concentration
to an area of low concentration.
A process requiring no energy
Made up of three processes:
– Diffusion
– Facilitated Transport
– Osmosis
3. Diffusion
The movement of molecules from an area of high
concentration to an area of low concentration
A natural process requiring no energy
Some molecules enter and leave cells through the
plasma membrane by diffusion.
Such molecules are:
1. Small noncharged molecules like urea
2. Water
3. Gases like oxygen and carbon dioxide.
4. Osmosis
The movement of water molecules across a semi-
permeable membrane, from an area of high water
concentration to an area of low water concentration
A natural process requiring no energy
An area of high water concentration has low solute
concentration, while an area of low water concentration
has high solute concentration
Solution tonicity (how relatively concentrated)
1. Isotonic: No water movement
2. Hypertonic: Water moves in.
3. Hypotonic: Water moves out
5. Facilitated transport
The movement of molecules from an area of high
concentration to an area of low concentration
A natural process requiring no energy
Unlike diffusion, a carrier or channel protein is required.
Such molecules are:
1. Some sugars
2. Water
3. Some amino acids
Note that these molecules are generally too big to simply diffuse on their own
6. Active Transport
The movement of molecules across the plasma
membrane from an area of low concentration
to an area of high concentration.
A process that requires energy
Made up of three processes:
– Active transport
– Endocytosis
– Exocytosis
7. Active Transport
The movement of molecules from an area of low
concentration to an area of high concentration. This is
also known as going against the concentration
gradient.
A process that requires energy
A protein carrier is also required.
Such molecules are:
1. Ions like Na+, K+ and Cl-
2. Some sugars
3. Some amino acids
8. Exocytosis
A process where very large molecules
(macromolecules) leave the cell by the formation
of vesicles from the plasma membrane. Molecules
like:
Digestive enzymes: Ex, Produced in the pancreas
and released in the small intestine.
Hormones: Ex, Insulin, produed in the pancreas,
released into the blood to regulate sugar levels.
9. Endocytosis
A process where very large molecules
(macromolecules) or even entire cells enter
the cell by the invagination of the plasma
membrane. Things like:
Cholesterol: Travels in the blood in protein-
lipid “bubbles” which enter cells by
endocytosis.
Bacteria: Are “eaten” by white blood cells
(the body’s “soldiers”) by endocytosis.
10. Endocytosis
A process where very large molecules
(macromolecules) or even entire cells enter
the cell by the invagination of the plasma
membrane. Things like:
Cholesterol: Travels in the blood in protein-
lipid “bubbles” which enter cells by
endocytosis.
Bacteria: Are “eaten” by white blood cells
(the body’s “soldiers”) by endocytosis.
