Structure and Function of the Cell Membrane

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

Cell Wall• Found only in plant cells and bacteria

cells• Main function is support

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)

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

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

Equilibrium• When molecules are evenly

spread throughout a space

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…

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.

Cells In Different Solutions

"ISO" means the same; water stays in equilibrium.

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

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?

Passive Transport• Requires no energy• Diffusion & Osmosis• Facilitated Diffusion: carrier

proteins “help” molecules across the membrane like a tunnel

ACTIVE TRANSPORT

• Requires the cell to use energy• Carrier Proteins or Pumps found in

the membrane move materials across• Open/close like a door

Endocytosis/Exocytosis

• Taking “in” or letting “out” large molecules by the cell

• Phagocytosis = “phood”, taking in food particles

• Pinocytosis = liquid substances