Cell BoundariesKeeping the world out of our cell

What are the boundaries?• 2 TYPES- cell membrane & cell wall• All cells are surrounded by a thin, flexible

barrier known as the cell membrane. • Many cells also produce a strong

supporting layer around the membrane known as a cell wall.

Cell Membrane

• What does it do???– The cell membrane regulates what comes in and out

of the cell.

• The composition of nearly all cell membranes is a double-layered sheet called a lipid bilayer. – Its made of lipids and it has two layers (bilayer)Called SELECTIVELY PERMEABLE

This means some things come in and other things are kept out.Usually bigger substances have to enter through a special protein doorway

This is a lipid bilayer

Cell Wall

• Why do we need a wall in the first place?

– The main function of the cell wall is to provide support and protection for the cell.

• Hmmm…• Cell walls are found in plants, algae, fungi, and many

prokaryotes.• The cell wall lies outside the cell membrane. • Most cell walls are porous enough to allow water, oxygen,

carbon dioxide, and certain other substances to pass through easily

Cellular Transport

Moving things on a cellular level

Passive Transport

• Two types – Diffusion– Osmosis

• How is that possible?• The cell membrane regulates movement of

dissolved molecules from the liquid on one side of the membrane to the liquid on the other side.

Diffusion

• Particles move from an area of HIGH concentration to LOW concentration– This process is called diffusion. – When the concentration of the solute is the

same throughout a system, the system has reached equilibrium (aka equal level)

AND DON’T FORGET NO ENERGY IS USED!!!

Diffusion at its best….

Remember High Concentration to Low Concentration

Facilitated Diffusion

• DIFFUSION with HELP

• Cell membranes have protein channels that act as carriers, making it easy for BIG molecules to cross.

• Hundreds of different protein channels have been found that allow particular substances to cross different membranes.

Osmosis• Osmosis is the diffusion of water (HIGH to

LOW) through a selectively permeable membrane.

Hypo vs. Hyper

• Water tends to diffuse from a highly concentrated region to a less concentrated region.

• If you compare two solutions, the more concentrated solution is hypertonic (“above strength”).

• The more dilute solution is hypotonic (“below strength”).

Isotonic

• Oh the bliss…

When concentrations of solutions are the same on both sides of a membrane, the solutions are isotonic (“same strength”).

• But always remember…is the water or the particles what’s moving???

THE WATER

Active Transport

• Sometimes cells move materials in the opposite direction from which the materials would normally move (low to high) This process is known as active transport.

• Active transport requires energy.

Endocytosis and Exocytosis

–  Endocytosis• process of taking material into the cell by means of

infoldings, or pockets, of the cell membrane. – TWO KINDS- Phagocytosis and Pinocytosis

» Phagocytosis- surround and package» Pinocytosis- surround and pinch off

– Exocytosis• Forces contents out of the cell