1. Movement Through a Membrane
The Cell: Part II

2. The cell membranes plays an important role in determining what enters and leaves the cell.
The cell/plasma membrane is made of a phospholipid bilayer. It can be selectively permeable.
Fluid mosaic model
Hydrophilic head
Hydrophobic tail

3. Passive Transport
Substances are moving from an area of high concentration to an area of low concentration
“going with the flow”
Does not require cell to use energy
Two types of passive transport are:
Diffusion
Osmosis

4. Diffusion is the movement of molecules across the membrane.

5. Osmosis is the diffusion of water across the membrane

6. Facilitated Diffusion
Movement of molecules with the aid of a carrier protein.

7. Types of solutions ISOTONIC solution- HypOtonic solution-
Same amount of water inside and outside of the cell membrane
Cell size remains the same
HypOtonic solution-
More water outside the cell than inside the cell membrane
Cell swells
Hypertonic solution-
More water inside the cell than outside the cell membrane
Cell shrinks

8. Active Transport
Substances are moving from an area of low concentration to an area of higher concentration
“going against the flow”
Active transport requires the input of energy from the cell

9. Endocytosis and Exocytosis
The engulfing of large particles into a cell is called endocytosis.
Special case – phagocytosis
The releasing of large particles out of a cell is called exocytosis.
Animation