1. OSMOSIS and DIFFUSION

2. Molecules are always moving
Molecules move randomly and bump into each other and other barriers

3. Concentration gradient
Concentration Gradient - change in the concentration of a substance from one area to another.

4. Diffusion
Molecules in solution tend to slowly spread apart over time. This is diffusion.

5. Diffusion MOVEMENT OF LIQUID OR GAS MOLECULES
from high concentration to a low concentration until the substance is evenly spread out.
IMPORTANCE:
lets food and oxygen into a cell
waste products such as carbon dioxide out of the cell

6. Diffusion [High] [Low] concentrated, high energy molecules
diffuse, low energy molecules

7. Diffusion continues until equilibrium is reached.
Equal distribution of molecules throughout the space.
This is why food coloring moves throughout a beaker of water
why odors smell strong at first and then disappear over time.
Equilibrium, a result of diffusion, shows the uniform distribution of
molecules of different substances over time as indicated in the
above diagram.

8. Definition of Osmosis Osmosis is the movement of water molecules,
from a region of high water concentration
to a region of low water concentration
ACROSS A SELECTIVELY PERMEABLE MEMBRANE.
LEARN THIS !!!!

9. Selectively Permeable?
A selectively permeable membrane is a
membrane with holes in it small enough for WATER to go through it easily.
Big molecules like starch, proteins and carbs can not fit through easily
Remember!!
A membrane controls what goes in and out of the cell.
Permeable means it allows substances to go through it.
See next slide…

10. Model of a Selectively Permeable Membrane
Water
Starch
Small molecules, such as water can pass through it.
Large molecules like starch can not pass through the membrane
Diagram shows the net flow of water

11. Osmosis

12. Over time molecules will move across the membrane until the concentration of solutes is equal on both sides. This type of solution is called ISOTONIC.

13. Cells in an isotonic solution
= concentrations
Conc. Inside = conc. Outside
same rate
Cell retains normal
size/shape
pressure
H2O
H2O
Water Molecule
Dissolved Molecule

14. Cells in an isotonic solution

15. PASSIVE TRANSPORT occurs without expenditure of energy
NO ENERGY IS USED BY THE CELL
move using their own kinetic energy
Particles go DOWN OR WITH their concentration gradient.
Diffusion and osmosis are PT
allows cells to get water, oxygen and other small molecules that they need
allows the cell to get rid of waste such as carbon dioxide.

16. Passive Transport by proteins
Passive transport of materials across the membrane using transport proteins is called facilitated diffusion.
Channel proteins
Plasma membrane
Concentration gradient

17. Passive Transport by proteins
Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through.

18. Active Transport against a concentration gradient
requires energy from the cell.
Cellular energy
Carrier proteins
Plasma membrane
Concentration gradient
Cellular energy

19. Active vs. Passive Transport
Passive Transport – does not require energy. Particles move from high to low concentration.
Active Transport – does require energy because molecules are moving from low to high concentration

20. Transport of Large Particles
Endocytosis
Exocytosis
Endocytosis
Exocytosis

21. Endocytosis too large to pass through the cell membrane.
The cell membrane can surround a large particle located outside the cell.
1. The membrane forms a sac around the particle.
2. Then the sac opens inside the cell.

22. Exocytosis
Large particle leave the cell in sacs too. Inside the cell, a sac forms around large waste particles.
1. The sac moves to the membrane and then opens outside the cell.
2. Waste particle move OUTSIDE the cell.

23. Cells in a hypotonic solution
hypotonic solution: dilute solution thus low solute concentration
In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell.
H2O
H2O
Water Molecule
Dissolved Molecule

24. Cells in a hypotonic solution
Plant cells swell beyond their normal size as pressure increases. (plants prefer this –it makes the leaves firm)

25. Cells in a hypertonic solution
concentrated solution, thus a high solute concentration
In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink
H2O
H2O
Water Molecule
Dissolved Molecule

26. Cells in a hypertonic solution
Plant cells lose pressure as the plasma membrane shrinks away from the cell wall. PLASMOLYSIS

27. Cytoplasm is a solution of water and solids
(solutes dissolved in the water).
Water moves into and out of cells because of the different concentrations of the solutes.
Different kinds of cells react differently depending on the solution they are in.
Below are examples of red blood cells in different types of solutions and shows what happened to the red blood cells.

28. Animal Cells in different solutions
A red blood cell in pure water, water will move into the cell and the cell will BURST (there is no cell wall to prevent this happening)
In a strong salt/sugar solution water will move out and the cell will SHRINK (the cell in described as CRENATED)

29. PLANT CELLS Hypotonic Solution Hypertonic Solution
Turgor Pressure builds in the cell and causes osmosis to stop
because of the rigid cell wall.
Plants will wilt when cells
lose water through osmosis.

30. Plant Cell in different solutions
In pure water – water will move in swelling the vacuole which pushes out against the cell wall.
The plant cell is described as TURGID.
The cell does not burst because of the cell wall.
Plant cell placed in
pure water
Water moves
Into the cell

31. Plant Cell in Strong Sugar Solution
In a strong salt or sugar solution – water will move out of the vacuole causing it to shrink.
The cytoplasm can also shrink away from the cell wall.
The plant cell is described as Plasmolysed or Flaccid.
Strong Sugar/Salt
Solution

32. As viewed under the microscope
ELODEA CELLS
As viewed under the microscope

33. THE END