The tight coiling and looping of the glomerular capillaries is functionally important, because it:
a. provides increased surface area for filtration
b. allows for more efficient reabsorption of water
c. provides smaller distance for diffusion
d. causes a decrease in gfr

(The correct option is A) Provides increased surface area for filtration.

Explanation:

Glomerular capillaries is known as a network of small blood capillaries which is called as a tuft, and situated at the starting of a nephron which is present in the kidney.

Through the glomerular filtration barrier, the blood is filtered across the capillary walls of the tuft, which helps to yield it's filtered of soluble substances, and water to a Bowman's capsule (cup like sac). Then filtered enter to the renal tube of the nephrons.

Glomerular capillaries important function is to provide increased surface area for filtration. So, the correct option is A.