Glomerular filtrate is
1. formed continuously by the process of ultrafiltration occurring at Malpighian corpuscles, in which the blood cells and the colloidal macromolecules are not allowed to pass across the filtering surface
2. the electrolyte free fluid collected within the lumen of Bawman's capsule
3. the protein free fluid collected within the lumen of Bowman's capsule
4. formed by the process of selective reabsorption

Options

A. 1, 2 and 3 are correct
B. 1 and 2 are correct
C. 2 and 4 are correct
D. 1 and 3 are correct

Answer

To solve the question regarding glomerular filtrate, we will analyze each of the provided options step by step.

### Step-by-Step Solution:

1. **Understanding Glomerular Filtration**:
- Glomerular filtrate is formed in the kidneys through a process called ultrafiltration, which occurs in the Malpighian corpuscles (also known as renal corpuscles). This involves the glomerulus (a tuft of capillaries) and Bowman's capsule.

**Hint**: Remember that the glomerulus and Bowman's capsule together form the Malpighian corpuscle.

2. **Analyzing Option 1**:
- Option 1 states that glomerular filtrate is formed continuously by ultrafiltration at the Malpighian corpuscles, where blood cells and colloidal macromolecules are not allowed to pass. This is true because during ultrafiltration, only small molecules (like water, ions, and small solutes) pass through while larger components like blood cells and proteins are retained in the bloodstream.

**Hint**: Focus on what is filtered out during ultrafiltration – only small molecules pass through.

3. **Analyzing Option 2**:
- Option 2 claims that glomerular filtrate is an electrolyte-free fluid collected in Bowman's capsule. This statement is false because glomerular filtrate contains electrolytes (like sodium, potassium, and chloride) dissolved in it.

**Hint**: Recall that glomerular filtrate is derived from blood plasma, which contains electrolytes.

4. **Analyzing Option 3**:
- Option 3 states that glomerular filtrate is a protein-free fluid collected in Bowman's capsule. This is true because during the filtration process, proteins are too large to pass through the filtration barrier and thus do not enter Bowman's capsule.

**Hint**: Consider the size of proteins compared to the filtration barrier in the kidneys.

5. **Analyzing Option 4**:
- Option 4 suggests that glomerular filtrate is formed by selective reabsorption. This is false because glomerular filtrate is formed by ultrafiltration, not by selective reabsorption, which occurs later in the nephron.

**Hint**: Differentiate between the processes of ultrafiltration and selective reabsorption in kidney function.

### Final Conclusion:
From the analysis:
- **Option 1** is correct.
- **Option 2** is incorrect.
- **Option 3** is correct.
- **Option 4** is incorrect.

Thus, the correct answer is that glomerular filtrate is represented by options **1 and 3**.