Principle organic constituent of a living being in order of relative abundance is

Options

A. Water
B. Protein
C. Lipid
D. DNA.

Answer

To determine the principal organic constituent of a living being in order of relative abundance, we will analyze each option provided:

### Step-by-Step Solution:

1. **Understanding the Question**: We need to identify the most abundant organic constituent in living organisms from the given options: water, protein, lipid, or DNA.

2. **Evaluating Water**:
- Water is essential for life and is involved in numerous metabolic processes.
- It acts as a solvent and transporter for various substances in the body.
- However, water is not classified as an organic molecule, so it cannot be the answer to our question.

**Hint**: Remember that organic molecules typically contain carbon, while water (H2O) does not.

3. **Evaluating Proteins**:
- Proteins are made up of amino acids and serve as the building blocks of cells.
- They play crucial roles in forming cell membranes and are essential for the structure and function of enzymes.
- Proteins are indeed one of the most abundant organic constituents in living organisms.

**Hint**: Think about the roles of proteins in the body and their structural importance.

4. **Evaluating Lipids**:
- Lipids are important for forming cell membranes and serve as energy storage molecules.
- They are produced by the smooth endoplasmic reticulum and are significant but are not as abundant as proteins in the overall composition of living organisms.

**Hint**: Consider how lipids compare to proteins in terms of abundance and function.

5. **Evaluating DNA**:
- DNA is the genetic material responsible for inheritance and contains the instructions for the development and functioning of living organisms.
- While crucial, DNA is not as abundant as proteins in terms of overall mass and quantity in the body.

**Hint**: Reflect on the role of DNA compared to proteins and how it contributes to the organism's structure.

6. **Conclusion**: After evaluating all options, we find that proteins are the most abundant organic constituents in living beings. Therefore, the correct answer is **B) Protein**.

### Final Answer:
**The principal organic constituent of a living being in order of relative abundance is: Protein.**