24) Active and Passive Transport

Passive Transport- substances cross the membrane without any energy inout from the cell.
Passive Processes: Diffusion and Filtration
Diffusion- is the movement of molecules (driven by kinetic energy) down a concentration gradient.
Types of Diffusion:
-Simple Diffusion- A net movement of particles from an area of their higher concentration to an area of their lower concentration, this is, along their concentration gradient. Kinetic energy is the energy source. Examples: movements of fats, oxygen, carbon dioxide through the lipid portion of the membrane.
-Facilitated Diffusion- Same as simple diffusion but, the diffusing substance is attached to a lipid-soluble membrane carrier protein or moves through a membrane channel. Kinetic energy is the energy source. Examples: movements of glucose and some ions into cells.
-Osmosis- Simple diffusion of water through a selectively permeable membrane. Kinetic energy is the energy source. Example: movement of water into and out of cells directly through the lipid phase of the membrane or via membrane pores.
Flitration- Movement of water and solutes through a semipermeable membrane from a region of higher hydrostatic pressure to a region of lower hydrostatic pressure, this is, along a pressure gradient. Hydrostatic pressure is the energy source. Examples: movement of water, nutrients and gases through a capillary wall (formation of kidney flitrate).

Active Processes: Active Transport and Vesicular Transport
Active Transport- the cell provides the metabolic energy (ATP) needed to move substances across the membrane.
-Primary Active Transport- Transport of substances against a concentration gradient across the plasma membrane by a solute pump, directly using energy of ATP hydrolysis (making ATP the energy source). Examples: Ions such as Na+ or K+
-Secondary Active Transport- Contransport of two solutes across the membrane. Energy is supplied by the ion gradient created by a primary active solute pump. Symporters move the transported substances in opposite directions across the membrane. ATP is the energy source. Examples: movement of polar or charged solutes.
Vesicular Transport-
-Exocytosis- Secrets or ejects substances from a cell, encloses in a membrane vesicle, which fuses with a plasma membrane and ruptures. This releases a substance to the exterior. ATP is the energy source. Examples: secretion of neurotransmitters, hormones or mucus.
-Endocytosis- happens through phagocytosis or pinocytosis. Phagocytosis is a large external particle that is surrounded by a "seizing foot" and becomes enclosed in a clathrin-coated vesicle. ATP is the energy source. Example: protective phagocytes such as white blood cells. Pinocytosis is fluid phase endocyotosis. The plasma membrane sinks beneath an external fluid droplet containing small solutes and a clathrin-coated vesicle is formed. Example: taking in dissolved solutes by absorptive cells of the kidney and intestine.