1. The Plasma Membrane
Maintaining a Balance

2. The Plasma Membrane
The plasma membrane is a SELECTIVELY PERMEABLE membrane that allows nutrients and wastes to enter and exit the cell
Homeostasis: maintaining balance in the cell

3. Selective Permeability
Selective Permeability – allows some molecules to pass through and keeps others out
E.g. Screen on a window
Water can freely enter and exit the cell. Other particles such as Na+ and Ca+ ions are only allowed in at certain times (selective permeability)

5. Phospholipid
The plasma membrane is composed of a PHOSPHOLIPID BILAYER (double layer)
A phospholipid molecule is a lipid which is composed of a glycerol, a phosphate, and two fatty acids
The two fatty acid tails of the phospholipid are NONPOLAR (not attracted to water) whereas the head of the phospholipid molecule is POLAR (attracted to water)

7. Polar Head
(glycerol + phosphate)
Nonpolar Tail
(fatty acids)

8. Phospholipid Bilayer
The two layers of phospholipid molecules make a sandwich with the fatty acid tails forming the interior of the membrane and the phospholipid heads facing the watery environments found inside and outside the cell

14. Cholesterol and Transport Proteins
Cholesterol is mixed into the plasma membrane and helps keep the fatty acid tails
from sticking together
Transport proteins span across
the plasma membrane and move
larger molecules through the
membrane

17. Cellular Transport

18. Diffusion
Water can pass freely through the plasma membrane by DIFFUSION
Diffusion – the movement of particles from an area of higher concentration to an area of lower concentration
Like gravity  High to Low
E.g. Perfume spreads from point of origin to evenly disperse around the room

21. Gas spreads out by diffusion!

22. Water
In the cell, WATER always moves to reach an equal concentration of both sides of the membrane
The diffusion of water across a semi- permeable membrane is called OSMOSIS

23. Osmosis
If two solutions with different solute concentrations are separated by a selectively permeable membrane (i.e. the plasma membrane), the water molecules will move from the solution with HIGHER WATER (lower solute) CONCENTRATION to the solution with LOWER WATER (higher solute) CONCENTRATION.
The solute doesn’t move; only the WATER moves

25. 90% Water
70% Water
80% Water
80% Water

26. Water moves from high concentration of water
to lower concentration of water
15% Sugar
(85% H2O)
H2O
H2O
30% Sugar
(70% H2O)
Cell
H2O
H2O
Environment

27. Facilitated Diffusion
Facilitated Diffusion – transport of materials across a membrane with the aid of transport proteins (no energy)
Proteins act like a gate or channel that opens and closes to let materials in and out

29. Osmotic Solutions
Isotonic Solution – the concentration of water is EQUAL on both sides of the membrane. Water moves in and out of the cell equally
Hypotonic Solution – the solute concentration is higher inside the cell than outside the cell. Water will move into the cell by osmosis and the cell will SWELL in size
Hypertonic Solution – the solute concentration is lower inside the cell than outside the cell. Water will move out of the cell by osmosis and cell will SHRINK in size

32. Concentration Gradient
CONCENTRATION GRADIENT - When there is an unequal concentration of solutes on different sides of a membrane
WITH concentration gradient
AGAINST concentration gradient

33. Passive Transport
PASSIVE TRANSPORT - Particles naturally move WITH the concentration gradient
High  Low
NO ENERGY is needed
Diffusion = passive
Osmosis = passive
Facilitated Diffusion = passive

34. Active Transport
Active Transport – moves materials AGAINST the concentration gradient
Low  High
REQUIRES ENERGY!
Active transport uses TRANSPORT PROTEINS + ENERGY to move materials from low concentration to high concentration

35. ENERGY!

37. Endocytosis/Exocytosis
Endocytosis – the whole cell engulfs something
Exocytosis – the whole cell ejects something