Which of the following statements is INCORRECT ?
I. The cell wall of plants is made up to homopolysaccharides while the cell wall of fungi is made up of heteropolysacchaerides.
II. The function of enzyme will stop if its tertiary structure is destroyed.
III. The cytoplasm contains r - thymidylic acid and d-uridylic acid as building blocks of nucleic acids.
IV. Arachidonic acid has 20 carbon atoms including the carboxyl carbon .

Options

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

Answer

To determine which of the statements is incorrect, let's analyze each statement one by one:

### Step 1: Analyze Statement I
**Statement I:** The cell wall of plants is made up of homopolysaccharides while the cell wall of fungi is made up of heteropolysaccharides.

- The cell wall of plants is primarily made up of **cellulose**, which is a homopolysaccharide (made of glucose units).
- The cell wall of fungi is primarily made up of **chitin**, which is also a homopolysaccharide (made of N-acetylglucosamine units).

**Conclusion:** This statement is **incorrect** because both plant and fungal cell walls are made of homopolysaccharides.

### Step 2: Analyze Statement II
**Statement II:** The function of an enzyme will stop if its tertiary structure is destroyed.

- Enzymes are proteins that have a specific three-dimensional structure (tertiary structure) that is crucial for their function.
- If the tertiary structure is destroyed (denaturation), the enzyme will lose its functionality.

**Conclusion:** This statement is **correct**.

### Step 3: Analyze Statement III
**Statement III:** The cytoplasm contains r-thymidylic acid and d-uridylic acid as building blocks of nucleic acids.

- The correct building blocks of nucleic acids are nucleotides.
- **Thymidylic acid** (dTMP) is a nucleotide that contains thymine, but it is not referred to as "r-thymidylic acid" (which is incorrect terminology).
- **Uridylic acid** (UMP) is the nucleotide that contains uracil, but it is not referred to as "d-uridylic acid" (which is also incorrect terminology).

**Conclusion:** This statement is **incorrect** due to the incorrect naming of the nucleotides.

### Step 4: Analyze Statement IV
**Statement IV:** Arachidonic acid has 20 carbon atoms including the carboxyl carbon.

- Arachidonic acid is a polyunsaturated fatty acid with **20 carbon atoms** in total, including the carboxyl carbon.

**Conclusion:** This statement is **correct**.

### Final Conclusion
Based on the analysis:
- Statement I is incorrect.
- Statement II is correct.
- Statement III is incorrect.
- Statement IV is correct.

The question asks for the INCORRECT statement. Therefore, both Statement I and Statement III are incorrect, but since the question asks for one, we can conclude that **Statement I** is the primary incorrect statement regarding the composition of cell walls.

### Answer:
The incorrect statement is **I**.

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