1. 3.5 Cells and Their Environment
Diffusion
Osmosis
Active transport
Bulk movement

2. Cell Membrane Cells must take in nutrients And eliminate wastes
Both must cross the cell membrane

3. Inside vs. Outside

4. Inside vs. Outside
We will talk in terms of substances outside the cell membrane vs. inside the cell membrane
We will look at the concentration of materials

5. Semi permeable Membrane
Lets certain molecules pass through the pores
Prevents other molecules from crossing

6. Semipermeable Membrane
Small molecules: water and sugars enter and leave freely
Large molecules: lipids, proteins, carbs, and ions can not pass through

7. Transport of Substance
Passive Transport
Active Transport

9. Passive Transport
Movement of substances across a membrane without using any energy
Goes “with” the concentration gradient
Substances move from high concentration of substances to low concentration of substances

10. Substance do not need energy, like climbing
No Energy Required
Substance do not need energy, like climbing
DOWN hill

11. Types of Passive Transport
Diffusion
facilitated diffusion
filtration
osmosis

13. Active Transport Uses energy to move substances across a membrane
Goes “against” the concentration gradient
From low concentration to high concentration

14. Substance need energy, like climbing
Active Transport
Area of High Concentration
Area of Low Concentration
Substance need energy, like climbing
UP hill

15. Diffusion Passive Transport Substances enter or exit a cell
Move “Down a concentration gradient”
From High to Low

16. No Energy Required

17. Substance do not need energy, like climbing
No Energy Required
Substance do not need energy, like climbing
DOWN hill

18. Water and Sugar Molecules

20. Facilitated DiffusionPT
Molecules need help of transport proteins
Water-soluble molecules and ions are helped across by transport proteins, due to the hydrophobic nature of the lipids that make up cell membranes.

22. Transport Proteins
Proteins embedded in the lipid bilayer of the cell membrane
Open up channels to let ions pass

25. Osmosis Passive Transport, like diffusion
The seeping of a water through a cell wall or cell membrane
When the concentration of the fluid is the same on both sides of the barrier, osmosis stops

26. Osmosis A solution consists of solvents and solutes
Cytoplasm is a solution of water and dissolved solutes
External cellular environment is also a water solution with solutes

27. Osmosis Look at solvent (water)
And solute (compound or ion or element)
Solvent and solutes move in OPPOSITE directions

28. Osmotic Effects of Solution Concentrations
Hypertonic solutions
Isotonic solutions
Hypotonic solutions

29. Hypertonic Solution
Concentration of solutes outside the cell is higher than inside the cell
Solutes move inside
Water moves outside
Cell Shrink

30. Isotonic Solution
Concentration of solutes outside the cell = the concentration inside the cell
NO OSMOSIS occurs

31. Hypotonic Solution
Concentration of solutes outside the cell is lower than it is inside the cell
Water moves into the cell
Salt moves out of the cell
Cells can explode

34. Osmosis Example
If blood cells (or other cells) are placed in contact with an isotonic solution, they will neither shrink nor swell.
If the solution is hypertonic, the cells will lose water and shrink (plasmolyze).
If the solution is hypotonic (or if pure solvent is used) the cells will swell;
the osmotic pressure that is developed may even be great enough to rupture the cell membrane.

35. Osmosis Examples
Saltwater from the ocean is hypertonic to the cells of the human body;
the drinking of ocean water dehydrates body tissues instead of quenching thirst.

36. Osmosis Examples
In plants osmosis is at least partially responsible for the absorption of soil water by root hairs
and for the elevation of the liquid to the leaves of the plant.
However, plants wilt when watered with saltwater or treated with too much fertilizer, since the soil around their roots then becomes hypertonic.

37. Active Transport
Involves a carrier protein to pump ions and molecules across a cell membrane
They use ATP for energy

39. Sodium-potassium pump
The protein pump that moves potassium ions into and sodium ions out of a cell.
In order for diffusion to occur…..
Cells need to keep a low concentration of Na ions, and high levels of K ions inside the cell
Outside cells , there are high concentrations of Na and low K
To keep the appropriate concentrations, the sodium-potassium pump, pumps sodium out and potassium in

42. Bulk Movement
Large molecules are “packaged” in vesicles and moved across the membrane
Exocytosis
Endocytosis

43. Exocytosis cellular secretion or excretion
Substances, in vesicles, are discharged from the cell by fusion of the vesicle to the outer cell membrane

44. Endocytosis Cells absorb material from outside their cell membranes
Materials enter the cell
Endocytosis can be of three forms:
Phagocytosis
Pinocytosis

45. Phagocytosis
The engulfing and ingestion of bacteria or other foreign bodies by phagocytes.

46. Pinocytosis
Introduction of fluids into a cell