Chapter 35, Problem 6STP

Summary Introduction

Introduction:

The body collects wastes, like toxins, waste products, and carbon dioxide that result from metabolism in the body. The excretory system removes these toxins and wastes from the body, regulates the amount of fluid and salts and maintains the pH of the blood. All of these functions help to maintain homeostasis.

Answer to Problem 6STP

Correct answer:

The correct answer is option (A) Blood enters nephrons of the kidneys, and excess water and wastes are filtered from the blood.

Explanation of Solution

Explanation/justification for the correct answer:

Option (A) Blood enters nephrons of the kidneys, and excess water and wastes are filtered from the blood. The kidneys are bean-shaped organs that filter out wastes, water and salts from the blood. Each kidney contains approximately one million filtering units called nephrons. So, the correct answer is option (A).

Explanation for incorrect answer:

Option (B) Urine leaves the kidneys through ureters. Blood enters nephrons of the kidneys, and excess water and wastes are filtered from the blood. The liquid waste product of kidneys is known as urine. Urine leaves the kidney through ducts named the ureters. Urine is then stored in the urinary bladder and exits the body through the urethra. But this statement does not describe how filtering occurs in the excretory system. So, this is an incorrect option.

Option (C) Water and nutrients are absorbed back into the blood. In the excretory system, much of the lost water and useful nutrients are reabsorbed back into the capillaries surrounding the renal tubule. This process is known as reabsorption. But only this process not describes the whole process of filtration. So, this is an incorrect answer.

Option (D) Water is added to excess nitrogenous wastes from the digestive system to form urine. Blood enters nephrons of the kidneys, and excess water and wastes are filtered from the blood. So, this is an incorrect answer.