Problem 48 - Objective Biology for NEET

Question

Mammalian kidney serve to excrete (a) Excess water, urea and amino acids (b) Excess salts, urea and excess water (c) Excess salts, excess water and excess amino acids (d) Excess salts, urea and water

Step-by-Step Solution

Answer

The correct answer should be (b) Excess salts, urea and excess water.

Step 1: Review the function of the kidney

The kidneys' primary function is to regulate the concentration of substances in the blood and excrete waste products from the body encased in a water solution.

Step 2: Analyze each option

Option (a) implies the kidneys excrete only excess water, urea, and amino acids, which is partially correct but incomplete. The kidney also regulates and excretes excess salts. Option (b) includes excess salts, urea and excess water which perfectly explains the primary function of kidneys. Option (c) suggests the excretion of excess amino acids, which is not the primary role of kidneys. Lastly, Option (d) does not differentiate between the regulatory function of kidneys regarding water levels, implying that all water is excreted which is incorrect.

Step 3: Choose the correct option

Based on the previous analysis, option (b) correctly outlines the key functions of the mammalian kidney.

Key Concepts

Excretion of Waste

The excretion of waste is an essential process in mammals for the removal of metabolic by-products that, if accumulated, would be toxic. The kidneys play a pivotal role in this process. Mammals metabolize nutrients to obtain energy, and during this metabolic process, by-products like urea, generated from the breakdown of proteins, and excess salts are formed.

The kidneys filter the blood, removing these waste products, along with excess water, to maintain the body’s chemical balance. They form urine, which collects in the bladder before being expelled from the body. This filtration system ensures that harmful compounds do not reach a concentration that could disturb the body's delicate equilibrium.

Urine Formation

Urine formation is a multi-step process involving filtration, reabsorption, and secretion. The kidneys are adept at conserving water when the body needs to retain it, releasing only excess water in urine. The ability to excrete waste efficiently is critical for overall health.

Regulation of Blood Composition

Beyond waste excretion, the kidneys have a paramount responsibility in regulating blood composition which is instrumental for homeostasis. They manage various ions and substances such as sodium, potassium, calcium, pH levels, and blood volume.

A stable internal environment is necessary for cells to function correctly, and the kidneys contribute to this stability by regulating osmolarity, which is the concentration of solutes in the blood. They adjust the reabsorption and secretion of ions and water to keep the blood’s osmolarity within a narrow range. This adjustment happens in the nephron, the functional unit of the kidney.

Blood Pressure Regulation

The kidneys also play a role in controlling blood pressure by managing the blood volume. They respond to changes in blood pressure by altering the amount of urinary excretion which, in turn, adjusts the volume of blood in circulation. This regulatory mechanism is crucial in maintaining cardiovascular health.

Homeostasis in Mammals

Homeostasis refers to the dynamic equilibrium in the internal environment of the body, and it is vital for the survival of mammals. The kidneys are major contributors to this balance by controlling the composition and volume of body fluids.

Homeostasis encompasses temperature regulation, pH balance, and osmoregulation, among others, relying heavily on the efficient functioning of the kidneys. Any disturbance in homeostasis can lead to a range of disorders, underscoring the importance of the kidneys in maintaining a conducive physiological state for cellular activity.

Osmoregulation and Acid-Base Balance

Kidneys help maintain osmoregulation by managing the concentration of water and solutes in the body fluids while also preserving acid-base balance by regulating the excretion of hydrogen ions and bicarbonate. Balancing these factors is key for metabolic processes and ATP production, the energy currency of cells. The kidneys’ multilayered roles are, therefore, essential for the constancy of the internal environment, an aspect of utmost importance in mammalian biology.