The major building block of an organism is...

1. Analyze the question The question asks for the "major building block" of an organism. This means the element that forms the backbone of the molecules that make up living things.

2. Explain the concept All the organic molecules in living organisms are built on chains or rings of carbon atoms:

• Carbohydrates (glucose, starch)
• Proteins (amino acids)
• Lipids (fats and oils)
• Nucleic acids (DNA and RNA)

Carbon is special because each atom can form four covalent bonds. It can bond with other carbon atoms and with hydrogen, oxygen, nitrogen and sulphur. This allows it to form long chains, branches and rings, which gives the variety of complex molecules needed for life. This is why biology is often called the study of "carbon-based life" and why organic chemistry is the chemistry of carbon compounds.

3. Go through the options

• A. Nitrogen: It is essential, since it is found in amino acids, proteins and nucleic acids. But it is a component of those molecules, not the backbone of all of them. Carbohydrates and lipids contain no nitrogen.
• B. Carbon: It is present in every organic molecule and forms the structural backbone. ✔
• C. Water: It is the most abundant compound in an organism (about 60-70% of body mass). However, it is a solvent and a medium for reactions, not the building block of organic structure. It is also a compound, not an element.
• D. Sulphur: It occurs only in small amounts, for example in some amino acids like cysteine and methionine.

4. Answer The major building block of an organism is Carbon, which is option B.

5. Tip Remember: "Carbon is the backbone, water is the medium." If a question asks about the backbone or basis of organic molecules, think carbon. If it asks about the most abundant substance in the body, think water. JAMB often tests this difference, so read the wording carefully.