Why are the openings in cell membranes are different sizes?
970004
to only allow certain types of proteins to go through it.  They go through the protein channels... aka glycoproteins\n\nhope this helps =)
86313
Each cell is like a plastic bag filled with a spaghetti soup of all the different cell components. But it's a very special plastic bag, because it is permeable - water and friendly chemicals can pass through it, but bad guys get shut out. Rather like the firewall works (or should work!) when you're on the internet. The cell membrane is the plastic of the bag.\n\n:-)\nDC\nwww.tigerworld.tv
246458
The cell membrane is made up of a phospholipid bilayer, with a polar phophate head and a nonpolar lipid tail. The polar head is hydrophilic, the nonpolar tail is hydrophobic. A fat molecule will face toward the nonpolar, hydrophobic tail.
793148
It has nothing to do with surface area/volume ratio of their cells. Surface area/volume ratio is only a factor when you are talking about single cell species. In multi-cell species, such as bears, humans, ants, elephants, trees,...... it is the number of the cells that determine their size: a baby has a smaller size than an adult human because he has fewer cells not because his cells are smaller than an adult.\nIn case of polar bear vs. black bears size, other than the number of the cells, the amount of fat they have reserved in their body is another factor.
750402
With the increase in cell size the ratio between surface area and volume decreases. A large cell will therefore  have less surface area compared to the volume to  cope with the demands of the cell as far as the exchange of materials between the extracellular environment and the cytoplasm is concerned.On the other hand a smaller cell will have large surface area to adequately meet the demands of the volume of the  cytoplasm.The cell volume depends upon r to the power 3 and the cell surface depends upon r(radius) to the power 2. This becomes the limiting factor for the growth of the cell.
667592
C\n\nThe ribosomes are far to small to see with a ligh microscope. Under an electron microscope, they look like tiny dots (of whatever color you stained them).\n\nAlso, you won't be able to make out the details of the cell membrane either, only that it exists.
607138
plant cells have cell walls to give them structure. they would be more box shaped where as animal cells would be more rounded since they dont have a cell wall.
113839
Endocytosis is when a cell takes outside material inside it.  The cell membrane is a phospholipid bilayer.  This means that that outer and inner surfaces of the memberane like to be with water and the center of the memberane likes to be with oil.    The cell membrane deforms to surround whatever it is trying to bring into the cell.  The membrance then closes around the stuff that it is engulfing.  At this point the cell is still completely surrounded by the membrane; however, there is a new, smaller membrane bound pocket inside of the cell.  That is endocytosis.  If the endocytosis is pH dependent, that means that this cellular process happens in a manner that is related to how acidic or basic the outside enviroment is.\n\nThis question might get a more detailed answer in the biology catagory.
773190
The cell will shrink when osmotic pressure is less out side of the membrane then in. It loses water to the outside trying to balance, therefore shrinking.
90731
Yes.  You should know that if you've looked at them under a light microscope.  This applies for pretty much all cells of the same type, since cells can be neither too big nor too small.  If they're too big, then information has a hard time travelling through the large amounts of space and cytoplasm, and the cell can't function.  If they're too small... not everything fits.
17547
OSMOSIS IS THE MOVEMENT OF WATER MOLECULES ACROSS THE CELL MEMBRANE.  IF THE OSMOTIC PRESSURE IS HIGH i.e THERE ARE MORE WATER MOLECULES INSIDE THE CELL THEN WATER MOVES OUT TO LESSEN THE PRESSURE.  IF THE OSMOTIC PRESSURE IS VERY LOW THEN WATER MOLECULES MOVE INTO THE CELL TO KEEP THE PRESSURE OUTSIDE AND INSIDE EQUAL.\n\n(IT IS RUDE TO WRITE IN ALL CAPITALS)
233869
You're probably referring to the plasma membrane. The interior is hydrophobic, while the exterior is hydrophillic. The phospholipids can translocate horizontally within the bilayer, but can't cross from one layer to the other. So, the membrane behaves like a fluid.  See MIT's website for more info. the link is below
702562
Because of osmosis (the diffusion of water through a membrane) the water will move from the higher concentration of water to the lower concentration of water. (From the solution with less sugar, to the solution with more sugar, because it has less water in it with the sugar taking up the space.)
771971
Cell membrane, or phospholipid bi-layer.
980593
Dialysis tubing can come in various pore sizes that allow selective passage of materials. This is like a cell membrane that is also selective, but not really in terms of the size of the material. It has to do with the polarity (cell membrane is bipolar-has polar head with long, non-polar tail, but two chains of this with non-polar ends facing inward on the membrane and polar heads facing the outside of the membrane). Polar molecules (such as Na+ or K+) need to go through membrane-bound protein channels or receptors.
900184
some cells to take in more. Cell permiablility.\n\nhttp://www.answers.com/topic/cell-permeability
886103
Vacuoles do this funcion......\nVacuoles are very big in plant cells, while they are smaller in animal cells...\nbut they do d same function