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

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.

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

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

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.

lipid-soluble molecules (O 2, CO 2, H 2 O) (extracellular fluid) (cytoplasm) Simple diffusion

water molecule drop of dye

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.

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

Figure 5.8 Osmosis Modifies the Shapes of Cells Onion cell osmosis

Osmosis 1.Describe the relationship of dissolved materials inside and outside of a cell in the following solutions: – Isotonic solutions: when the concentration of two solutions is the same

Osmosis 1.Describe the relationship of dissolved materials inside and outside of a cell in the following solutions: – Hypotonic solution: when comparing two solutions, the solution with the lesser concentration of solutes (higher concentration of water)

Osmosis 1.Describe the relationship of dissolved materials inside and outside of a cell in the following solutions: – Hypertonic solution: when comparing two solutions, the solution with the greater concentration of solutes (low concentration of water)

Isotonic solution Equal concentration of water molecules and solutes

Hypotonic solution the solution with the lesser concentration of solutes

Hypotonic solution the solution with the greater concentration of solutes on the outside (low concentration of water)

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.

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.

Maintaining Cellular Homeostasis Exocytosis is 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.

Endocytosis and Exocytosis

Homeostasis Maintaining internal equilibrium Passive and Active Transport