Download Cell Theory`s 3 Main Ideas

Cell Theory’s 3 Main Ideas
1. All organisms are composed of one or
more cells
2. The cell is the basic unit of
organization of organisms
3. All cells come from preexisting cells
-a cell divides to form two identical cells
Two Basic Types of Cells
• Prokaryotes: Cells that lack internal
membrane-bound structures
– Usually unicellular organisms such as
bacteria
• Eukaryotes: Contains membrane-bound
structures called organelles
– Usually multi-cellular organisms such as
plants and animals
Prokaryotes
Eukaryotes
Cells Have Boundaries
• Both types of cells contain a plasma
membrane which creates a boundary
between the cell and its environment
• The membrane allows only certain
materials to enter or leave (Selective
Permeability). This helps the cells
maintain homeostasis
– Kind of like the screen in a window; It lets
air in but keeps bugs out
Structure of Plasma Membrane
• The membrane is composed of a
phospholipid bilayer which contains
hydrophobic (water fearing) fatty acid
tails and hydrophilic (water loving)
phosphate heads
– This is known as the fluid mosaic model
Fluid Mosaic Model
Cholesterol
Transport
Protein
The Bilayer Also Has…
• Cholesterol: Helps stabilize the
phospholipids by making sure they don’t
stick together
• Transport Proteins: Span the entire
membrane to allow larger molecules to
pass through
Osmosis
• Although the plasma membrane can
stop molecules that cannot pass freely
through it, it does not stop the
movement of water
• Diffusion of water across the membrane
is called Osmosis