1. Chapter 5 Homeostasis and Cell Transport

2. Passive Transport
Substances crossing the cell membrane without any input of energy is known as passive transport
Diffusion: simplest form of passive transport; the movement of molecules from an area of high concentration to low concentration

3. Diffusion Utilizes a concentration gradient
Driven entirely by kinetic energy of molecules
Moving from high to low concentrations
Moving “down” a concentration gradient
Eventually equilibrium is reached: the concentration of molecules will be the same throughout the space the molecules occupy

4. Passive Transport

5. Osmosis
Osmosis: water molecules diffusing across a cell membrane from an area of higher concentration to lower concentration.
Does not expend energy (passive transport)
Net direction of osmosis depends on the concentration of solutes on the inside and outside of the cell

6. Osmosis

7. Osmosis
When the concentration of solute molecules outside of the cell is lower than the concentration in the cytosol, the solution outside is hypotonic to the cytosol

8. Osmosis
When the concentration of solute molecules outside the cell is higher than the concentration in the cytosol, the solution outside is hypertonic to the cytosol

9. Osmosis
When the concentrations of solutes outside and inside the cell are equal, the outside solution is said to be isotonic to the cytosol

11. Osmosis

12. Osmosis
Some cells, such as the animal Paramecium, have contractile vacuoles to physically remove water from their bodies

13. Facilitated Diffusion
Used for molecules that cannot readily pass the plasma membrane
Requires no energy, relies on concentration gradient and the use of carrier proteins in the cell membrane

14. Diffusion through Ion Channels
Ion channels transport ions across a membrane from a higher concentration to a lower concentration
Ex: Na+, Cl-, K+
Ions are not soluble across the membrane, so ion channels help them
Each channel usually specific to one ion
Some are always open, some have “gates”

15. Ion Channels

16. Active Transport
Movement of materials from a low concentration to a high concentration, or “up” their concentration gradient is known as active transport
Often utilize proteins, known as “cell membrane pumps” to move substances across the membrane

17. Active Transport
Utilizes the proteins within the membrane and energy (ATP) to move substances across the membrane against its concentration gradient
Ex: Sodium-Potassium Pump

18. Sodium-Potassium Pump

19. Movement in Vesicles
Endocytosis: process by which cells ingest external fluid, macromolecules, and large particles
Utilizes a vesicle for transport
Two main types:
Pinocytosis
Phagocytosis

20. Movement in Vesicles
Pinocytosis: involves transport of solutes or fluids (cellular drinking)
Phagocytosis: movement of large particles or whole cells (cellular eating)

21. Movement in Vesicles
Exocytosis: process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface then fuses with the membrane to let the substance out of the cell