1. Cell TRANSPORT SB1d. Explain homeostasis and describe the movement of materials through the cell membrane. Explain the impact of water on life processes eq: how does the cell membrane help the cell maintain homeostasis?

2. Cell Transport
 The cell must move different substances into and out of the cell
 This happens in a variety of ways…
 Sometimes the cell has to use energy, sometimes they do not

3. Passive Transport
 Diffusion - passive transport of substances DOWN a concentration gradient (from high to low
concentration)
 Concentration gradient - one area has a higher concentration than another area
 Equilibrium - when a space is filled evenly
 Diffusion is simplest type of passive transport  Some substance diffuse through lipid bilayer
 Others though transport proteins

4. Diffusion  Cell membrane is selectively permeable
 Nonpolar interior of lipid bilayer repels ions and most polar molecules
 These substances are prevented from diffusing across membrane
 Very small or nonpolar molecules can diffuse across the membrane down their concentration gradient

5. Simple Diffusion
 Moves small, nonpolar molecules directly through lipid bilayer
 Ex-
 O2  CO2

6. Facilitated Diffusion
Moves ions and polar molecules that simple diffusion cannot
Transport proteins help these substances diffuse through the cell membrane
Two types:
Channel protein
Carrier protein

7. Channel Proteins
 Ions, sugars, and amino acids can diffuse with help of channel proteins
 Proteins, sometimes called pores, serve as tunnels through the lipid bilayer
 Each channel allows the diffusion of a specific substance
 Ex - only sodium ions can pass through sodium ion channels

8. Carrier Protein
 Transport substances that fit within their binding site
 (1)Carrier protein binds to specific substances on one side of cell membrane
 (2)Binding causes protein to change shape
 (3)As shape changes, the substance is moved across the cell membrane and released on other side

9. Facilitated Diffusion

10. Diffusion

11. Model of Diffusion

12. Osmosis
 Definition - diffusion of water across selectively permeable membrane
 Type of diffusion (passive transport)
 From high to low concentration
 Allows cells to maintain water balance as environment changes
 Pass through water channels
 Protein channels specific to water..

13. Osmosis
 There are three possibilities for the direction of water movement:
 Water moves out - (hypertonic solution)
 Causes cell to shrink
 Water moves in - (hypotonic solution)
 Causes cell to swell
 Cell could burst if it swells too much
 Plant cells have rigid cell wall to prevent this  No net water movement - (isotonic solution)
 No change in cell volume

14. Osmosis

15. Hypertonic, Hypotonic, and Isotonic Solutions

16. Active Transport
 Transports substances against concentration gradient
 Low to high concentration
 Active Transport - requires energy
 Most energy supplied directly or indirectly in the form of ATP (adenosine triphosphate)

17. Pumps  Substances bind to carrier proteins in low
concentrations, released in higher concentration
 Carrier proteins function as “pumps” - move
substances against their concentration gradient called membrane pumps

18. Movement in Vesicles
 Many substances, like proteins and polysaccharides, are too large to be transported by carrier proteins
 So, they are moved across the cell membrane by vesicles
 The movement of a substance into a cell by a vesicle is called endocytosis
Pinocytosis- “cell drinking”
Phagocytosis- “cell eating”
 The movement of a substance by a vesicle to the outside of a cell is called exocytosis

19. ENDOCYTOSIS

20. EXOCYTOSIS