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Answer:
<em><u>Osmosis and facilitated diffusion</u></em> are two forms of passive transport that are integral to cellular transport mechanisms.
Explanation:
Cells surrounded by a bilipid layer or plasma membrane are amphiphilic, with their polar, hydrophilic lipid heads facing outward, while their hydrophobic non-polar lipid tails facing each other inward.
Although lipid-soluble molecules travel quickly through the bilayer, traveling across its surface into the cell is often difficult for charged and large molecules. Thus, transport proteins, pores and gated channels, transmembrane channels, embedded within the membrane, help to preserve selective permeability.
Across plasma membranes as a form of passive transport in cells, substances move via:
- osmosis - water molecules readily pass through the membrane; the molecules move from high concentration regions to low concentration regions at will through the membrane- they move down their concentration gradient
- facilitated diffusion - channel proteins allow charged ions to move across the membrane. Sodium ions are able to pass freely through specialized sodium channel pores into some cells. These channels always remain open- the ions move down their concentration gradient.
