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(O2, CO2, H2O)

(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

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.

Passive and Active Transport

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