In organic chemistry and materials science, long chain molecules made up of repeating carbon based units are collectively known as what?

Introduction / Context:
This question tests your understanding of basic terminology related to large molecules in chemistry and biology. It asks what we call long chain molecules formed by repeating smaller carbon containing units. These substances are very important in plastics, synthetic fibres, rubber, proteins and many natural materials.

Given Data / Assumptions:

• The focus is on long chain molecules composed of repeating units.
• The repeating units are carbon based, consistent with organic chemistry.
• Options include ribosomes, hydrocarbons, polymers, enzymes and none of these.
• We assume standard textbook definitions for each term.

Concept / Approach:
Polymers are substances made up of many repeating small units (monomers) linked together in long chains. The term “polymer” comes from Greek roots meaning “many parts.” Most polymers in organic chemistry are carbon based, including polyethylene, PVC, proteins, DNA and many synthetic materials. Hydrocarbons are compounds made only of hydrogen and carbon, which can be small or large, but the key concept of repeated units forming a chain is captured specifically by the term polymer. Ribosomes and enzymes are complex biological structures or proteins, not general names for long chain molecules.

Step-by-Step Solution:
1) Recognise that the question highlights long chains of molecules built from repeating units, which is the defining feature of polymers.2) Polymers can be natural, like cellulose and proteins, or synthetic, like nylon and polyethylene, and they consist of many monomer units joined by covalent bonds.3) Hydrocarbons are simply compounds of hydrogen and carbon; small molecules like methane and ethane are also hydrocarbons but are not long chains of repeating units.4) Ribosomes are cellular organelles involved in protein synthesis; they are structures made from RNA and protein, not what the question is describing.5) Enzymes are proteins that act as catalysts in biochemical reactions, and while they are polymers of amino acids, the general term the question is asking for is more basic and broader: polymers.6) Therefore, the correct answer is polymers, the general name for long chain molecules formed by repeating units.

Verification / Alternative check:
Textbooks in polymer chemistry define a polymer as a very large molecule composed of many repeating subunits, called monomers. Examples include polystyrene, made from styrene monomers, and proteins, made from amino acid monomers. While many polymers are predominantly carbon based, the key feature in the question is the concept of “long chains” and “repeating units,” which fits the definition of polymers exactly. Hydrocarbons may form long chains but do not necessarily consist of repeated identical units, and the term hydrocarbon does not emphasise repetition the way polymer does.

Why Other Options Are Wrong:
Ribosomes: These are complex cellular organelles built from RNA and proteins that assemble amino acids into proteins; they are not long chain molecules of repeating monomers.
Hydrocarbons: This term covers all compounds containing only hydrogen and carbon, including small molecules like methane; it is not restricted to long chain, repeating unit molecules.
Enzymes: These are specific proteins that catalyse biochemical reactions; they are examples of biological polymers but not the general term the question is asking for.
None of these: This would be correct only if none of the listed terms matched, but “polymers” clearly does.

Common Pitfalls:
Some students may be tempted to choose hydrocarbons because they associate long chains of carbon atoms with this word. However, hydrocarbons include both short and long molecules and do not imply repeating unit structures. Another trap is to focus on biological examples and select ribosomes or enzymes, but those refer to specific cellular components or proteins rather than the general category of long chain, repeating unit molecules. To avoid confusion, always link the idea of many repeating monomers with the term polymer.

Final Answer:
Long chain molecules made up of repeating carbon based units are called polymers.