No Net Cell Movement

Cells must move materials through membranes and throughout cytoplasm in order to maintain homoeostasis. The movement is regulated because cellular membranes, including the plasma and organelle membranes, are selectively permeable[1]. The purpose of an automatic flow of molecules is to create equilibrium on each side of the membrane. In order for molecules to pass through the membranes, there must be pores. The size of the pore determines what molecules can cross. Due to the size and polarity, only some molecules fit through the pores while others are repelled[3]. The simplest form of movement is diffusion, in which solutes move from an area of high concentration to an area of low concentration; diffusion is directly related to molecular kinetic energy[1]. Note that membranes are not in the definition[2]. In diffusion, molecules are always moving around, so even if
As for the dialysis bag with the distilled water, the water diffused both ways across the membrane through the dialysis bag pores. Since both sides were water, there was a small amount of net movement. However, considering both sides were both water, there should have been roughly no net movement because the solution was isotonic, not an increase of roughly five percent. For the 0.2, 0.4, 0.6 0.8, and 1.0 Moles of sucrose solutions, the bag gained mass. The water had to diffuse across the membrane into the bag to space out the sucrose molecules because the beaker contained no sucrose. The sucrose was unable to diffuse across the dialysis tubing because the molecules were too large for the pores (as referenced in the previous paragraph). This part experiences osmosis because only the water, not the sucrose, diffused across the membrane to close the gap between the solute and solvent concentrations. This process of osmosis was a result of the selectively permeable membrane, which allowed only certain sized molecules to