7.2 The Plasma Membrane

Main Idea: The plasma membrane helps to maintain
homeostasis in the cell
Function of the Plasma
Membrane

The process of maintaining an organisms internal
environment is homeostasis

The plasma membrane is primarily responsible for
maintaining homeostasis
Plasma Membrane

Thin flexible boundary between a cell and its
environment
 Allows
nutrients into the cell and waste and other
products to leave the cell
Selective Permeability

The plasma membrane allows some substances
to pass through and keeps others out
Structure of the Plasma
Membrane

The plasma membrane is made of a phospholipid bilayer

This is 2 layers of phospholipids arranged tail to tail
Structure of the Plasma
Membrane

The heads of the phospholipids are hydrophilic


They like water
The tails are hydrophobic

They hate water
Structure of the Plasma Membrane

The hydrophobic lipids do not allow water
soluble substances to cross easily
 This
helps keep the environment outside and inside
the cell separate
Other components of the
plasma membrane

Proteins are found in 3 places in the plasma membrane

Outside the cell


Receptors- transmit signals to the inside of the cell
Inside the cell

Anchor the membrane to the inner support structure


Gives the cell its shape
Spanning the membrane

Moves substances through the membrane
Other components of the
plasma membrane

Cholesterol


Prevents the phospholipid bilayer from sticking together
Carbohydrates

Helps to identify chemical signals