Maintaining Cellular Homeostasis

1. Maintaining Cellular Homeostasis How do organisms regulate their body’s internal environment?

2. Maintaining Cellular Homeostasis • The cell membrane is selective – only allowing certain materials to pass through. It is comparable to a gatekeeper – controlling the traffic of substances passing in and out of the cell.

4. Maintaining Cellular Homeostasis • The cell membrane’s selective permeability is essential for maintaining cellular homeostasis – the steady state of operations inside the cell. Plasma Membrane

5. Maintaining Cellular Homeostasis • The specific processes involved in the movement of substances in and out of the cell and thereby helping to maintain cellular homeostasis are listed below: • Diffusion • Facilitated diffusion • Osmosis • Active transport • Endocytosis • Exocytosis

6. Maintaining Cellular Homeostasis • Diffusion is the process by which molecules move from where they are greater in concentration to where they are lesser in concentration. • The cell does not have to use any of its energy for this process. The molecules move by their own kinetic energy.

7. Simple diffusion (extracellular fluid) lipid-soluble molecules (O2, CO2, H2O) (cytoplasm)

8. drop of dye water molecule

11. Maintaining Cellular Homeostasis • Facilitated diffusion is the process in which substances move from greater to lesser concentration across the cell membrane with the assistance of carrier proteins.

13. Maintaining Cellular Homeostasis • Osmosis is the diffusion of water across a selectively permeable membrane.

15. Figure 5.8 Osmosis Modifies the Shapes of Cells Onion cell osmosis

16. Maintaining Cellular Homeostasis • Active Transport is the movement of a substance across a cell membrane against a concentration gradient; it requires the cell to expend energy.

17. Passive and Active Transport

18. Maintaining Cellular Homeostasis • Endocytosis is the process by which a cell surrounds and engulfs substances. It occurs in two forms: pinocytosis and phagocytosis. • Pinocytosis is the type of endocytosis in which a cell engulfs fluids. • Phagocytosis is the type of endocytosis in which a cell engulfs large particles or whole cells.

21. Maintaining Cellular Homeostasis • Exocytosisis the process in which a cell releases large molecules into the cell’s external environment. It works like this: a vesicle inside a cell fuses with the cell membrane and releases its contents to the external environment.

22. Endocytosis and Exocytosis

23. Homeostasis • Maintaining internal equilibrium