Cell growth

Basic Cell Function: Exchanging Material

“ Selective permeability: the cell membrane allows some substances to pass while blocking others.

Substances with free passage across membranes include:

Enzymes

Glucose

Electrolytes

Diffusion: movement of solutes toward lower solute concentrations.

Facilitated diffusion: movement of solutes toward higher concentrations using a carrier molecule.

Lipid-soluble substances pass through the membrane directly by simple diffusion.

Facilitated diffusion and active transport (as shown in Figure 01.F06A/B):

Water-soluble molecules can diffuse through membranes with the help of proteins (facilitated diffusion).

Other proteins use energy from ATP to move substances against their concentration gradients (active transport).

Osmosis: passive movement of water/solvent across a membrane toward higher solute concentrations (osmotic pressure).

Consequences: lysis and crenation depend on the osmotic conditions.

Endocytosis: bringing substances into the cell.

Phagocytosis: engulfing large particles or cells.

Pinocytosis: uptake of extracellular fluid.

Exocytosis: release of materials from the cell.

Figure references to aid understanding:

Fig. 01.F03 shows selective permeability maintaining homeostasis by allowing some molecules to pass and blocking others.

Fig. 01.F04 shows lipid-soluble substances passing via simple diffusion.

Fig. 01.F06A/B illustrate facilitated diffusion and active transport.