Urea has a molecular weight lower than 20 MWCO, so it should be able to diffuse through a 20 MWCO membrane. If urea is not able to diffuse through a 20 MWCO membrane, it may be due to factors like the membrane being damaged or having a different pore size than expected, or the presence of additional physical or chemical barriers that prevent urea diffusion.
The 20 MWCO membrane has a molecular weight cutoff that is lower than the molecular weight of urea, preventing urea from passing through the pores of the membrane. This size exclusion property of the membrane hinders the diffusion of urea molecules across it.
Passive diffusion - Urea has its own concentration gradient so it will go from an area of high concentration through the cell membrane into an area of lower concentration.
It works much like your real kidneys. Your kidneys work essentially with a "Salt imbalance". One half of a kidney has a higher saline content than the other half; when blood passes through, urea is "pulled" into the saltier side.
Urea is primarily produced in the liver as a waste product of protein metabolism. It is formed through the urea cycle, which converts ammonia, a toxic byproduct of amino acid breakdown, into urea, allowing for safe excretion through urine. Additionally, some urea is produced in other tissues, but the liver is the main site of its synthesis.
Urea is predominantly carried in urine, which is produced by the kidneys and excreted through the urinary system. In the bloodstream, urea is carried in the form of urea nitrogen and is filtered by the kidneys to be excreted in urine.
The 20 MWCO membrane has a molecular weight cutoff that is lower than the molecular weight of urea, preventing urea from passing through the pores of the membrane. This size exclusion property of the membrane hinders the diffusion of urea molecules across it.
Because Na has MW of ~23 and Cl has MW of ~35...both of which are small enough to pass through a molecular weight cut off (MWCO) of 50 (don't add there molecular weights together). urea has ~ MW of 60 so it's too big to cross membrane.
The average diffusion rate of urea through a 200 MWCO (Molecular Weight Cut-Off) membrane would depend on various factors such as concentration gradient, temperature, and membrane properties. Typically, higher MWCO membranes allow for faster diffusion rates of smaller molecules like urea due to their larger pore sizes. Specific experimental data would be needed to calculate the exact diffusion rate in this scenario.
urea
nephrons
In the dialysis experiment, only two substances were able to diffuse out of the dialysis tubing into the beaker due to the size of their molecules and the selective permeability of the dialysis membrane. The membrane allows smaller molecules, such as glucose and urea, to pass through while restricting larger molecules like starch or proteins. This selective permeability is essential for simulating biological processes, where cells selectively allow certain substances to enter or exit. Thus, only those small enough to fit through the pores of the dialysis tubing were able to diffuse into the surrounding solution.
During dialysis, urea, creatinine, excess electrolytes (such as potassium or sodium), and excess fluid are some of the solutes that typically diffuse from the patient's blood into the dialysis solution.
nacl diffuse in plasma membrane because there are protein channels that allows certain ions to diffuse around the membrane, like sodium and chloride ions, please note that these channel proteins are selectively permeable meaning sodium channels only allow sodium to enter the cell and so on... urea diffuses into the pm the same way through facilitated diffusion of certain protein channels glucose diffuse into the pm as a part of secondary active transport, which means it uses ATP indirectly. it diffuses in the process called symport
Urea moves from the fetus's blood to the mother's blood primarily through the placenta via diffusion. As the fetus metabolizes proteins, urea is produced and enters the fetal bloodstream. The concentration gradient allows urea to diffuse across the placental membrane into the maternal circulation, where it can then be excreted by the mother's kidneys. This process helps maintain proper nitrogen balance for both the fetus and the mother.
Passive diffusion - Urea has its own concentration gradient so it will go from an area of high concentration through the cell membrane into an area of lower concentration.
First of all, the filtration in dialysis doesn't happen in the tubing. Rather it happens in an artificial kidney called the dialyzer. It's essentially a dense bundle of thousands of fibers which make up the filter itself. The fibers allow the blood to pass through the dialyzer and the potassium and bicarbonate solution used to mix with the blood crosses over the fibers, cleaning the blood via filtration. MWCO (molecular weight cut off) in dialysis simply means the amount of molecules that are allowed to pass through the membranes. Proteins are too big to pass by design as we don't want to "wash away" the good stuff. Wastes like urea, nitrogen etc are allowed to pass through and out of the blood before the blood returns to the patient. Generally, the bigger the patient, the more filtration is required, so the higher the MWCO is. Hope this helps!
The Kidneys, where the blood/urea thing takes place.