1. Structure and Function of the
Cell Membrane

2. Cell Membrane
• Gatekeeper
• Regulates what comes in and out
of the cell
• Main components: proteins and
phospholipids
• The cell membrane is selectively
permeable
• Allows some things through without energy,
but not everything

3. Cell Wall
• Found only in plant cells and bacteria
cells
• Main function is support

4. Cell membrane parts
• phosopholipids
• made of two sides: head and tail
• the head is hydrophillic (able to
interact with water)
• the tail is hydrophobic (not able to
interact with water)

5. Cell membrane parts
• carrier proteins
• allow larger or difficult molecules to get
through the membrane
• sometimes they require energy to
open/close like a door
• other times they simply act as a tunnel

6. Diffusion
• The movement of molecules from
an area of high concentration to an
area of low concentration
• Molecules tend to “spread out”
• Requires no energy

7. Equilibrium
• When molecules are evenly
spread throughout a space

8. Osmosis
• The diffusion of water across a
membrane
• H2O molecules are able to go in
between the phospholipids based on
size and a slight electrical charge.
• Water will travel to where there is a
lower concentration
• If you add something like salt to the solution…

9. Rule for Osmosis:
Water will get sucked to
wherever there is a higher
concentration of salt.
The following slides illustrate what direction water
travels if a cell is placed in different solutions.

10. Cells In Different Solutions
"ISO" means the same; water stays in
equilibrium.

11. Hypo = less Cell fills with
water and may
burst, or
organelles called
“contractile
vacuoles”
remove excess
water

12. Hyper = more Cell will shrink or
die, plant leaves
wilt and droop.
Why is it
dangerous to
drink sea
water?
Why does
pouring salt
on a slug kill
it?

13. Passive Transport
• Requires no energy
• Diffusion & Osmosis
• Facilitated Diffusion: carrier
proteins “help” molecules
across the membrane like a
tunnel

14. ACTIVE TRANSPORT
• Requires the cell to use energy
• Carrier Proteins or Pumps found in
the membrane move materials across
• Open/close like a door

15. Endocytosis/Exocytosis
• Taking “in” or letting “out” large
molecules by the cell
• Phagocytosis = “phood”, taking in
food particles
• Pinocytosis = liquid substances