Why sand and blood cells cannot be filtered?

Sand cannot be filtered because the size of sand particles is much larger than the size of the pores in the filter paper. The pores in filter paper are typically less than 10 micrometers in diameter, while sand particles can range in size from 100 to 1000 micrometers in diameter. This means that sand particles are too large to fit through the pores in the filter paper.

Blood cells can be filtered because the size of blood cells is smaller than the size of the pores in the filter paper. Red blood cells are typically 7-8 micrometers in diameter, while white blood cells are typically 10-12 micrometers in diameter. This means that blood cells are small enough to fit through the pores in the filter paper.