Passive and active transport

Video explaining the differences of active and passive transport:

Passive transport - is a movement of biochemicals and other atomic or molecular substances across cell membranes. Unlike active transport, it does not require an input of chemical energy, being driven by the growth of entropy of the system. The rate of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins. The four main kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis. 
 - The solutes move down the concentration gradient, or from a HIGH to LOW concentration.
 - The types of passive transport are:

1. Diffusion - see #1
2. Facilitated diffusion - see #3 
3. Filtration - Filtration is movement of water and solute molecules across the cell membrane due to hydrostatic pressure generated by the cardiovascular system. Depending on the size of the membrane pores, only solutes of a certain size may pass through it. For example, only albumins (the smallest of the proteins) can pass through the small membrane pores of the Bowman's capsule in the kidneys. On the other hand, the membrane pores of the liver cells are very large, allowing a variety of solutes to pass through and be metabolized.
   
4. Osmosis - see #2

Examples: 

1. Passive transport occurs in the kidneys and the liver, and in the alveoli of the lungs when they exchange oxygen and carbon dioxide.
2. Diffusion of oxygen into an aerobically respiring cell.
3. Diffusion of carbon dioxide out an aerobically respiring cell.

Active transport - The movement of molecules across a cell membrane in the direction against their concentration gradient, i.e. moving from a LOW concentration to a HIGH concentration. 

Usually associated with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. If the process uses chemical energy, such as from ATP, it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient. Active transport uses cellular energy, unlike passive transport, which does not. (So active transport is a good example of a process for which cells require energy.)

 Examples: 

1. Uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants.
2. Metal ions, such as Na⁺, K⁺, Mg²⁺, or Ca²⁺, require ion pumps or ion channels to cross membranes and distribute through the body.
3. Sodium pump
4. In the epithelial cells of the stomach, gastric acid is produced by hydrogen potassium ATPase, an electrogenic pump.

Comparison -                                                   Active                                                 Passive

Definition	Active Transport uses ATP to pump molecules AGAINST/UP the concentration gradient. Transport occurs from a low concentration of solute to high concentration of solute. Requires cellular energy.	Movement of molecules DOWN the concentration gradient. It goes from high to low concentration, in order to maintain equilibrium in the cells. Does not require cellular energy.
Types of Transport	Endocytosis, cell membrane/sodium-potassium pump & exocytosis	Diffusion, facilitated diffusion, and osmosis.
Types of Particles Transported	proteins, ions, large cells, complex sugars.	Anything soluble (meaning able to dissolve) in lipids, small monosaccharides, water, oxygen, carbon dioxide, sex hormones, etc.
Examples	phagocytosis, pinocytosis, sodium/potassium pump, secretion of a substance into the bloodstream (process is opposite of phagocytosis & pinocytosis)	diffusion, osmosis, and facilitated diffusion.
Importance	In eukaryotic cells, amino acids, sugars and lipids need to enter the cell by protein pumps, which require active transport.These items either cannot diffuse or diffuse too slowly for survival.	It maintains equilibrium in the cell. Wastes (carbon dioxide, water, etc.) diffuse out and are excreted; nutrients and oxygen diffuse in to be used by the cell.
Functions	Transports molecules through the cell membrane against the concentration gradient so more of the substance is inside the cell (i.e. a nutrient) or outside the cell (i.e. a waste) than normal. Disrupts equilibrium established by diffusion.	Maintains dynamic equilibrium of water, gases, nutrients, wastes, etc. between cells and extracellular fluid; allows for small nutrients and gases to enter/exit. No NET diffusion/osmosis after equilibrium is established.

Similarities - Both movements depend upon the concentration gradient (Passive- substance moves towards the gradient. Active- substance moves against the gradient. Both involve ion movement. Both use ion channels to move ions across the cell membrane, in or out of the cell. And finally, both transport molecules through the cell membrane.