Which of the following statements is INCORRECT?
I. Human kidneys can produce urine nearly six times more concentrated than the initial filtrate formed.
II. An increase in body fluid volume can switch on the osmoreceptors and stimulate ADH.
III. Substance like glucose, amino acids, `Na^+` , etc., in the filtrate, are reabsorbed actively by the renal tubule whereas the nitrogenous wastes are absorbed by passive transport
IV. Each kidney has nearly one million complex tubular structures called nephrons which are the functional units.

Options

A. I and II
B. III and IV
C. I, II and III
D. II, III and IV

Answer

To determine which statement is INCORRECT, we will analyze each statement one by one.

### Step 1: Analyze Statement I
**Statement I:** Human kidneys can produce urine nearly six times more concentrated than the initial filtrate formed.

- **Analysis:** This statement is incorrect. Human kidneys can concentrate urine, but the maximum concentration is typically about four times that of the initial filtrate, not six times.

### Step 2: Analyze Statement II
**Statement II:** An increase in body fluid volume can switch on the osmoreceptors and stimulate ADH.

- **Analysis:** This statement is also incorrect. An increase in body fluid volume actually inhibits osmoreceptors, leading to a decrease in the secretion of Antidiuretic Hormone (ADH). ADH is stimulated when body fluid volume decreases.

### Step 3: Analyze Statement III
**Statement III:** Substances like glucose, amino acids, Na+, etc., in the filtrate are reabsorbed actively by the renal tubule whereas the nitrogenous wastes are absorbed by passive transport.

- **Analysis:** This statement is correct. Glucose, amino acids, and sodium ions are reabsorbed actively in the renal tubules, while nitrogenous wastes like urea are typically reabsorbed by passive transport.

### Step 4: Analyze Statement IV
**Statement IV:** Each kidney has nearly one million complex tubular structures called nephrons which are the functional units.

- **Analysis:** This statement is correct. Each human kidney contains approximately one million nephrons, which are indeed the functional units responsible for filtering blood and producing urine.

### Conclusion
After analyzing all the statements, we find that the INCORRECT statements are:

- **Statement I** is incorrect because the concentration of urine is about four times the initial filtrate, not six.
- **Statement II** is incorrect because an increase in body fluid volume inhibits osmoreceptors and decreases ADH secretion.

Thus, the answer to the question is that **Statements I and II are incorrect.**