Reading: Cell Transport

Week 4: Cell Transport Processes and Homeostasis

Imagine a house without windows or doors – nothing can come in or out
Imagine a house with holes instead of windows and doors – everything could go in and out without your control
A house with windows and doors allows you to control what comes in and out of the house, just like the plasma membrane of the cell

Passive Transport

-Simple diffusion
-Osmosis
-Facilitated diffusion

Active Transport

-Protein pumps – ie the sodium-potassium pump
-Vesicle transport: exocytosis, endocytosis

Vocab

Homeostasis: Process of maintaining a stable environment inside a cell or an entire organism.
Concentration Gradient: A measurement of how much the concentration of a substance changes across a distance.
Passive Transport: Substances cross the cell membrane without the cell providing energy.
Diffusion: A substance moves through a membrane from an area of high concentration to an area of low concentration.
Osmosis: The diffusion of water molecules across a membrane.
Facilitated Diffusion: Diffusion with the help of transport proteins.
Transport Protein: Special proteins in the membrane.
Active Transport: A substance moves against the concentration gradient (uses energy from cells).
Sodium-Potassium Pump: When this pump is in operation, sodium ions are pumped out of the cell, and potassium ions are pumped into the cell. Both ions move from areas of lower to higher concentration.
Vesicle Transport: Type of transport in which very large molecules cross the cell membrane.
Endocytosis: Type of vesicle transport that moves a substance into the cell. The plasma membrane completely covers the substance, a vesicle pinches off from the membrane, and the vesicle carries the substance into the cell.
Exocytosis: Type of vesicle transport that moves a substance out of the cell. A vesicle containing the substance moves through the cytoplasm to the cell membrane. Then, the vesicle membrane fuses with the cell membrane, and the substance is released outside the cell.