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Section 4-1  What is homeostasis?  Cells maintain homeostasis by controlling the movement of substances across the cell membrane.

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Presentation on theme: "Section 4-1  What is homeostasis?  Cells maintain homeostasis by controlling the movement of substances across the cell membrane."— Presentation transcript:

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2 Section 4-1

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

4  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  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  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  The diffusion of molecules across the cell membrane is the simplest type of passive transport

9  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 is a form of passive transport  3 possibilities of water movement 1. Water moves out 2. Water moves in 3. No net movement

11  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  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  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  Transport proteins provide passageways for polar molecules and ions to pass through the cell membrane  Each channel only allows a certain substance through

15  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  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  Carrier proteins carry specific substances across the membrane  They carry substances down their concentration gradient  Facilitated diffusion uses no energy

18  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

20  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  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

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23  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  e/content/cat_040/ html e/content/cat_040/ html

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26  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  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  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  Receptor proteins may bind with ion channels  Channels open when signal molecules bind to the protein  Important in nervous system

30  Acts as a signal molecule in the cytoplasm  Amplifies the signal from the first signal molecule

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


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