Desmosomes are most abundant in tissues that are subject to considerable stretching (skin) Tight junctions firmly bind with each other at points of direct contact to seal passageway. Passage must occur through the cells not between them. Glucose is an example of a large, poorly lipid soluble particles that must gain entry to the cell. Diffusion uniform spreading out of molecules because of their random intermingling. Net diffusion the difference between two opposing movements. Diffusion is crucial to survival of every cell and important for homeostatic activities. Steady state is when molecules from both sides are moving the same amounts. Greater the difference in concentration, the faster the rate of net diffusion. During exercise we exhale more co2 to coincide with the fact that we are creating much more. More permeable the membrane is to a substance, the more rapid the substance can diffuse down its concentration gradient.