23. A tight junction is a junction in which a series of integral protein molecules in the plasma membranes of adjacent cells fuse together forming an impermeable junction circling the cell. A desmosome is an anchoring junction where mechanical couplings are scattered like rivets along the sides of abutting cells that prevent their separation. Gap junctions are communicating junctions that allow chemical substances to pass between adjacent plasma membranes that are very close.
24. Substances that pass through the plasma membrane can pass through either actively or passively. In a passive process, substances cross the membrane without the use of any energy input from the cell. At the risk of being obvious it is a more passive form of transportation because of the lesser use of energy than active transport. Active transport processes are when the cell provides the metabolic energy or ATP needed to move the given substance across the membrane. Passive processes can include diffusion and filtration and active processes very regularly use pumps or some sort of physical transporter to get the substance across with the use of energy.
25. The role of glycocalyx which is the fuzzy, sticky, carbohydrate rich area in the cells surface is to provide highly specific biological markers by which approaching cells have the ability to recognize each other. It works similarly to the way that a sperm would recognize an ovum.