1. KEY CONCEPT The cell membrane is a barrierKEY CONCEPT The cell membrane is a barrier
that separates a cell from the externalthat separates a cell from the external
environment.environment.

2. Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.

3. Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane has two major functions.The cell membrane has two major functions.
cell membrane

4. Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane has two major functions.The cell membrane has two major functions.
o forms a boundary between inside and outside of the
cell
cell membrane outside cell
inside cell

5. Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane has two major functions.The cell membrane has two major functions.
– forms a boundary between inside and outside of the cell
– controls passage of materials
cell membrane outside cell
inside cell

6. Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.

7. cell membrane
Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane is made of a phospholipidThe cell membrane is made of a phospholipid
bilayer.bilayer.

8. cell membrane
Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane is made of a phospholipid bilayer.The cell membrane is made of a phospholipid bilayer.
• There are other molecules embedded in the membraneThere are other molecules embedded in the membrane..
protein
cholesterol
proteincarbohydrate
chain
protein channel

9. cell membrane
Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane is made of a phospholipid bilayer.The cell membrane is made of a phospholipid bilayer.
• There are other molecules embedded in the membrane.There are other molecules embedded in the membrane.
• TheThe fluid mosaic modelfluid mosaic model describes the membrane.describes the membrane.
protein
cholesterol
proteincarbohydrate
chain
protein channel

10. Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane is selectively permeable.The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.

11. Cell membranes are composed of twoCell membranes are composed of two
phospholipid layers.phospholipid layers.
• The cell membrane is selectively permeable.The cell membrane is selectively permeable.
Some molecules can cross the membrane
while others cannot.

12. KEY CONCEPT Materials move across membranes
because of concentration differences.
3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis
Concentration Gradient: when there is a
difference in concentration between two areas

13. Passive transport does not require energy input from a
cell.
• Molecules can move across the cell membrane
through passive transport.
• There are two types of
passive transport.
• osmosis
• diffusion
3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

14. Diffusion and osmosis are types of passive
transport.
• Molecules diffuse down a
concentration gradient.
• How would you define
DIFFUSION?!
3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

15. Diffusion and osmosis are types of passive
transport.
• Osmosis is the diffusion of water molecules across a
semipermeable membrane.
3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis

16. Diffusion and osmosis are types of passive transport.
• There are three types of solutions.
• isotonic
3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis
• hypotonic
• hypertonic

17. Some molecules can only diffuse through transport
proteins.
• Some molecules cannot easily diffuse across the cell
membrane.
• Facilitated diffusion is
diffusion through transport
proteins.
3.4 Diffusion and Osmosis3.4 Diffusion and Osmosis