<P> Filtration is movement of water and solute molecules across the cell membrane due to hydrostatic pressure generated by the cardiovascular system . Depending on the size of the membrane pores, only solutes of a certain size may pass through it . For example, the membrane pores of the Bowman's capsule in the kidneys are very small, and only albumins, the smallest of the proteins, have any chance of being filtered through . On the other hand, the membrane pores of liver cells are extremely large, but not forgetting cells are extremely small to allow a variety of solutes to pass through and be metabolized . </P> <P> Osmosis is the movement of water molecules across a selectively permeable membrane . The net movement of water molecules through a partially permeable membrane from a solution of high water potential to an area of low water potential . A cell with a less negative water potential will draw in water but this depends on other factors as well such as solute potential (pressure in the cell e.g. solute molecules) and pressure potential (external pressure e.g. cell wall). There are three types of Osmosis solutions: the isotonic solution, hypotonic solution, and hypertonic solution . Isotonic solution is when the extracellular solute concentration is balanced with the concentration inside the cell . In the Isotonic solution, the water molecules still moves between the solutions, but the rates are the same from both directions, thus the water movement is balanced between the inside of the cell as well as the outside of the cell . A hypotonic solution is when the solute concentration outside the cell is lower than the concentration inside the cell . In hypotonic solutions, the water moves into the cell, down its concentration gradient (from higher to lower water concentrations). That can cause the cell to swell . Cells that don't have a cell wall, such as animal cells, could burst in this solution . A hypertonic solution is when the solute concentration is higher (think of hyper - as high) than the concentration inside the cell . In hypertonic solution, the water will move out, causing the cell to shrink . </P>

What is an example of passive transport across a cell membrane