Questions: The color of urine is determined mainly by a. diet b. filtration rate c. byproducts of red blood cell breakdown d. filtration efficiency

The answer is the third one (c): byproducts of red blood cell breakdown.

Explanation for each option:

a. Diet: While diet can influence the color of urine (for example, eating beets can cause urine to appear red), it is not the main determinant of urine color.

b. Filtration rate: The filtration rate in the kidneys affects the concentration of urine but not its color. It determines how much water and solutes are filtered from the blood, which can affect urine concentration but not the primary color.

c. Byproducts of red blood cell breakdown: This is the correct answer. The primary pigment responsible for the color of urine is urochrome, which is a byproduct of the breakdown of hemoglobin from red blood cells. This gives urine its characteristic yellow color.

d. Filtration efficiency: Similar to filtration rate, filtration efficiency affects how well the kidneys filter blood but does not directly determine the color of urine.

In summary, the color of urine is mainly determined by the byproducts of red blood cell breakdown, specifically the pigment urochrome.