Selective Permeable

Directions: Follow along and fill out your notes. Answer the questions on your own :)

Please start on this page

Balanced internal condition of cells

Also called equilibrium

Maintained by plasma or cell

membrane controlling what enters
& leaves the cell

2

Plasma Membrane

 The plasma membrane is

the flexible outer layer of
cells.

(inside of cell wall if present)
 Has three main jobs:

1.

Separate cells from the
outside

2.

Protect cells from the
environment

3.

Decides what can enter
(or exit) the cell

Selective permeability: the ability that

allows some molecules to pass into the
cell while keeping others out

>> Check for Understanding

How does a window screen
show selective
permeability?

Directions: Use the following slides to help you complete this page. Ask for help if you need it :)

Please flip to this page

What are membranes made of?

Membranes are made up of molecules called

phospholipids.

Phosphate
and glycerol

What are membranes made of?

Hydrophillic:
Mixes with water

“HATES”
water →

​Hydrophobic:

What are membranes made of?

To keep their non-
polar tails away
from water,
phospholipids
form a two-sided
layer called a
bilayer.

Water

Water

No Water

Other Membrane Components

Turns out that the cell membrane is NOT

this simple:

Other Membrane Components

There are other parts to the membrane,

including cholesterol, proteins, and
carbohydrates

Cholesterol: Holding it Together

Cholesterol is mixed in with the phospholipids

to keep the tails from sticking together.

This gives the cells more stability

Transport Proteins: The Doors to
the Cell

Some molecules have trouble crossing the

membrane… Why???

Transport proteins help molecules enter or exit

the cell.

Other Parts: Sending Signals

Other proteins and carbohydrates stick out from

the cell; they act as signals for other cells to
read.

The Fluid Mosaic Model

The parts of the cell membrane are not held

in place; they flow around the cell like boats
in water. This is called the fluid mosaic
model.