Antibodies that help defend the body against pathogens belong to which major class of biological macromolecules?

Introduction / Context:
This question checks your knowledge of the basic nature of antibodies, which are essential components of the immune system. Knowing that antibodies are proteins and not lipids, carbohydrates or nucleic acids is fundamental for understanding topics such as immunology, vaccination and protein structure. The correct answer identifies the major macromolecular class to which antibodies belong.

Given Data / Assumptions:
- The question refers to antibodies that defend the body against foreign antigens.- Several classes of biological macromolecules are listed: proteins, lipids, carbohydrates, nucleic acids and mineral salts.- You are expected to recall which class includes immunoglobulins.- No numerical calculation is required, only conceptual understanding.

Concept / Approach:
Antibodies, also called immunoglobulins, are Y shaped molecules produced by B lymphocytes and plasma cells. They are complex proteins composed of two heavy chains and two light chains, linked by disulphide bonds. Each chain is made from amino acids, the building blocks of proteins. Although antibodies may have carbohydrate groups attached, their core structure and function clearly classify them as proteins. Lipids serve mainly in energy storage and membrane structure, carbohydrates provide energy and structural support, and nucleic acids store genetic information. Therefore, we look for the option that associates antibodies with proteins.

Step-by-Step Solution:
Step 1: Recall the general definition of an antibody as a protein that specifically binds to an antigen.Step 2: Remember that immunoglobulins are made of polypeptide chains, which are long chains of amino acids.Step 3: Recognise that amino acids are the building blocks of proteins, not lipids, carbohydrates or nucleic acids.Step 4: Evaluate each option and identify which macromolecule class matches this description.Step 5: Select proteins such as immunoglobulin molecules as the correct answer.

Verification / Alternative check:
An alternative check is to think of laboratory techniques such as protein electrophoresis, where immunoglobulins appear in the gamma globulin fraction, confirming that they are proteins.Immunology textbooks always refer to antibodies as protein molecules produced in response to antigens.There is no similar description of antibodies as lipids, carbohydrates or nucleic acids, which confirms the choice.

Why Other Options Are Wrong:
Option B is wrong because lipids include fats, oils and steroids and are mainly used for energy storage and membrane structure, not specific antigen binding.Option C is wrong because carbohydrates such as starch and glycogen are used for energy storage and structural support, not for recognising pathogens.Option D is wrong because nucleic acids like DNA and RNA store and transfer genetic information, rather than directly binding antigens as antibodies do.Option E is wrong because mineral salts have structural and regulatory roles but are not highly specific antigen binding molecules.

Common Pitfalls:
One pitfall is forgetting that many functional molecules in the body are proteins and thinking of antibodies as a separate category rather than a subset of proteins.Another mistake is to be distracted by the presence of carbohydrate side chains on some antibodies and to incorrectly classify them as carbohydrates.Keeping in mind that the primary structure is a polypeptide chain helps you confidently place antibodies in the protein category.

Final Answer:
Antibodies that help defend the body against pathogens are proteins such as immunoglobulin molecules.