What happens when the value of glucose is zero?

This sounds like a homework question. A glucose level of zero is not compatible with life. It is not clear what you mean by being filtered out of the blood and reabsorbed. Given how this question is worded I assume that you are referring to the kidneys handling of glucose. The glucose molecule is not too large to be filtered by the basement membrane of Bowman's capsule of the glomerular apparatus which is the functional unit of the kidneys. The nephron is comprised of a proximal tubule, the ascending loop of Henle, and the distal convoluted tubule. Glucose may be detected in the urine of diabetics and non-diabetics alike. There is however no good correlation between blood glucose levels and urine glucose levels. Most of the glucose is not filtered out of the blood envelope and thus most of the glucose does not therefore enter the nephron. Normally most but not all of the glucose is reabsorbed. The clearance of glucose decreases with age but it is not relatively high in an adult. If I am understanding the question correctly I do not believe that the correct answer is given. I may be over-interpreting the question and I may be offering an answer that is more complex that your course work requires. If I may be of further assistance please let me know. I wish you the very best of health and in all things may God bless.