Phosphorus is an essential element found in living organisms and plays a crucial role in various biological processes. It is mainly found in the form of phosphate ions (PO4^3-) in biological systems. Phosphorus is a constituent of nucleic acids and cell membranes, making option B the correct answer.

Cell Membrane:
- The cell membrane is a selectively permeable barrier that surrounds the cell, separating its internal environment from the external environment.
- Phospholipids, the main components of the cell membrane, consist of a hydrophilic phosphate head and hydrophobic fatty acid tails.
- The phosphate group of the phospholipid contains phosphorus, making phosphorus a constituent of the cell membrane.

Nucleic Acids:
- Nucleic acids, including DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), are essential molecules that store and transmit genetic information.
- Phosphorus is a key component of nucleotides, the building blocks of nucleic acids.
- The phosphate group in nucleotides contains phosphorus, contributing to the structure and function of nucleic acids.

Cell Wall:
- The cell wall is a rigid structural layer found in plants, bacteria, fungi, and some protists.
- While the cell wall contains various components like cellulose, chitin, or peptidoglycan depending on the organism, phosphorus is not a primary constituent of the cell wall.

Chlorophyll:
- Chlorophyll is a pigment found in plants and algae that plays a critical role in photosynthesis, the process by which plants convert light energy into chemical energy.
- Chlorophyll molecules contain a porphyrin ring structure with a central magnesium ion, but no phosphorus.

In conclusion, phosphorus is a constituent of cell membranes and nucleic acids, making option B the correct answer. While phosphorus is not a primary constituent of the cell wall or chlorophyll, it is still an essential nutrient for all living organisms.