The 4 types of Cellular Transport Mechanisms

Diffusion: is the tendency of molecules to spread into an available space. This tendency is a result of the intrinsic thermal energy (heat) found in all molecules at temperatures above absolute zero. Without other outside forces at work, substances will move/diffuse from a more concentrated environment to a less concentrated environment. No work is performed for this to happen, as diffusion is a spontaneous process.

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Osmosis: is a process in which a fluid passes through a semipermeable membrane, moving from an area in which a solute such as salt is present in low concentrations to an area in which the solute is present in high concentrations. The end result of osmosis, barring external factors will be equal amounts of fluid on either side of the barrier, creating a state which is known as "isotonic." The fluid most commonly used in demonstrations of osmosis is water, and osmosis with a wide variety of fluid solutions is key for every living organism on Earth, from humans to plants. 

Plants use osmosis to absorb water from the ground

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Facilitated Diffusion: is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. Some molecules and ions such as glucose, sodium ions and chloride ions are unable to pass through the lipid bi-layer of cell membranes. Through the use of ion channel proteins and carrier proteins that are embedded in the cell membrane these substances can be transported into the cell. Ion channel proteins allow specific ions to pass through the protein channel. The ion channels are regulated by the cell and are either open or closed to control the passage of substances into the cell.Carrier proteins bind to specific molecules, change shape an then deposit the molecules across the membrane. Once the transaction is complete the proteins return to their original position.

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Active Transport: The movement of ions or molecules across a cellular membrane from a lower to a higher concentration, requiring the consumption of energy.