The amount of water re-absorbed as urine flows along the tube depends on :
(I) How much excess water there is in the body
(II) How much of dissolved waste is there to be excreted
(III) How much of excess glucose is to be excreted
(IV) How much of salt and amino acid is to be excreted.

Options

A. Only (I)
B. Both (I) and (II)
C. Both (I) and (III)
D. (I), (II) and (IV)

Explanation

To determine the factors that influence the amount of water reabsorbed as urine flows along the nephron tubes, we need to analyze each of the given statements:

1. **Excess Water in the Body**: The amount of water reabsorbed is directly related to how much excess water is present in the body. If the body has excess water, less water will be reabsorbed, resulting in more dilute urine. Conversely, if the body is dehydrated, more water will be reabsorbed to conserve water, leading to more concentrated urine.

2. **Dissolved Waste**: The amount of dissolved waste in the body also affects water reabsorption. If there is a higher concentration of waste products (like urea), the kidneys will need to reabsorb more water to help excrete these wastes effectively. Therefore, more dissolved waste leads to more water being reabsorbed.

3. **Excess Glucose**: The relationship between excess glucose and water reabsorption is not direct. While glucose is filtered by the kidneys, it is usually reabsorbed completely under normal circumstances. Excess glucose in the urine (as seen in diabetes) does not directly dictate the amount of water reabsorbed, as glucose does not require additional water for its excretion in the same way that waste products do.

4. **Salt and Amino Acids**: The excretion of salts and amino acids can influence water reabsorption. If there are higher levels of salts and amino acids that need to be excreted, the kidneys will also need to reabsorb more water to help facilitate this process.

**Conclusion**: Based on the analysis, the factors that influence water reabsorption in the nephron are:
- (I) The amount of excess water in the body
- (II) The amount of dissolved waste to be excreted
- (IV) The amount of salt and amino acids to be excreted

Thus, the correct options that affect the amount of water reabsorbed are (I), (II), and (IV).