1. Cells and Their Environment

2. Section 4-1
Passive transport

3. Review What is homeostasis?
Cells maintain homeostasis by controlling the movement of substances across the cell membrane

4. Random Motion and Concentration
Passive transport is movement across the cell membrane that does not require energy
Substances travel from areas of high concentration to areas of low concentration
The difference in the concentration of a substance across the space is the concentration gradient

5. An substance of high concentration will move into a lower concentration until it is in equilibrium or equal

6. Movement of Substances
Particles of a substance will move randomly
If there is a concentration gradient (uneven concentration) then diffusion occurs
Diffusion is the movement of a substance from an area of high concentration to low caused by the random movement of particles

7. Movement of substances cont…
Many molecules and ions dissolve in the cytoplasm and outside of the cell
The concentration of substances is different inside and outside of the cell
Molecules will diffuse, to equalize, and need to pass through the cell membrane
Selectively permeable

8. Movement of substances cont…
The diffusion of molecules across the cell membrane is the simplest type of passive transport

9. Water Diffuses In and Out
Water molecules are small and can diffuse through the cell membrane easily
Osmosis is the diffusion of water molecules through a selectively permeable membrane

10. Osmosis Osmosis is a form of passive transport
3 possibilities of water movement
Water moves out
Water moves in
No net movement

11. Water Moves Out When water diffuses out of the cell, the cell shrinks
A solution that causes a cell to shrink is hypertonic (too much water goes out)

12. Water Moves In When water moves into the cell, the cell swells
A solution that causes a cell to swell because of osmosis is hypotonic
Too much water goes in

13. No Water Moves
If the outside and inside of the cell have the same concentration of water molecules, then water diffuses in and out at the same rate
No net movement
A solution that produces no change is isotonic

14. Proteins Help Transport Substances
Transport proteins provide passageways for polar molecules and ions to pass through the cell membrane
Each channel only allows a certain substance through

15. Diffusion Through Ion Channels
Sodium Na+, Potassium K+, Ca 2+ and chlorine Cl-, are important in cell functions
Ion channels are a doughnut shaped transport protein for ions like Na+ to pass through

16. Diffusion Through Ion Channels
Some pores are always open, others are closed by gates
The rate of movement of a substance across the membrane is determined by the concentration gradient
An ions movement across the membrane is determined by its charge
The inside of a cell is usually negative

17. Facilitated Diffusion
Carrier proteins carry specific substances across the membrane
They carry substances down their concentration gradient
Facilitated diffusion uses no energy

18. Facilitated Diffusion
Step 1: molecule outside of cell binds to carrier protein
Step 2: carrier protein transports molecule across membrane
Step 3: molecule is released in the cell

19. Section 4.2
Active transport

20. Active transport
Cells must transport certain amino acids, sugars, and other substance from the cytoplasm to surrounding fluids
Low concentration to high concentration
The concentration gradient will cause those substances to move back into the cell
The transport of a substance across a membrane against its concentration gradient is active transport

21. Sodium Potassium pump
This is one of the most important membrane pumps in animal cells
The sodium-potassium pump is a carrier protein that transports 3 sodium ions out of a cell and two potassium ions into the cell
Sodium is more concentrated outside the cell and potassium is more concentrated inside
Both ions are actively transported
The energy needed to power the pump is supplied by ATP

22. Sodium-Potassium pump

23. Vesicles Move Substances
Proteins and polysaccharides are too big to be moved by carrier proteins
These substances are moved by vesicles
Movement into the cell by a vesicle is endocytosis
Movement out of the cell by a vesicle is exocytosis
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24. Endocytosis

25. Exocytosis

26. How Cells Communicate
Cells need to be able to send and receive signals to each other
Cell release signal molecules that carry info to other cells
Hormones

27. How Cells Communicate
The cell membrane contains special proteins that bind to signal molecules to receive messages
Receptor proteins bind to a specific signal molecule allowing the cell to respond to the signal

28. Receptor Proteins
Most receptor proteins are embedded in the lipid bilayer of cell membrane
Binding a receptor protein to a signal molecule changes the activity of the receiving cell
Changes 3 ways

29. Changes in Permeability
Receptor proteins may bind with ion channels
Channels open when signal molecules bind to the protein
Important in nervous system

30. Second Messengers Acts as a signal molecule in the cytoplasm
Amplifies the signal from the first signal molecule

31. Enzyme Action Receptor proteins may act as enzymes
They may speed up reactions when the receptor protein and signal molecule bind
May also activate other enzymes