Final answer:
Colloid osmotic pressure is higher for plasma proteins due to the inability of these proteins to cross the semipermeable capillary membrane, leading to a higher concentration in the plasma compared to the interstitial fluid and thus promoting reabsorption of fluids into the capillaries.
Step-by-step explanation:
Colloid osmotic pressure is higher for plasma proteins. The plasma proteins, such as albumin, which are suspended in blood, cannot move across the semipermeable capillary cell membrane and therefore remain in the plasma. This results in blood having a higher colloidal concentration compared to tissue fluid, which in turn attracts water from the tissue fluid back into the capillaries due to the osmotic gradient. The blood colloidal osmotic pressure (BCOP) is thus higher than the interstitial fluid colloidal osmotic pressure (IFCOP), which is very low because interstitial fluid contains few proteins.
This significant difference in osmotic pressure across the capillary walls accounts for the reabsorption of fluids, and it is essential for maintaining the fluid balance within the body.