Macromolecules and Lipids: TEAS Practice Question with Answer & Explanation

Understanding the chemistry of macromolecules is a core requirement for the TEAS Science section. To answer this question correctly, you must distinguish between the chemical structures of saturated and unsaturated fats and how those structures affect their physical state.

The Correct Answer: C

Saturated fats are called "saturated" because every available bond on the carbon chain is occupied by (or "saturated" with) a hydrogen atom. Because there are no double bonds between the carbon atoms, the fatty acid chains are straight and linear. This straight shape allows the molecules to pack together very tightly, which is why saturated fats (like butter or lard) are typically solid at room temperature.

Why the Other Options are Incorrect

• A is incorrect: This choice swaps the definitions. Saturated fats actually lack double bonds. It is the absence of double bonds that allows them to be solid, not liquid.
• B is incorrect: This is the opposite of the truth. Saturated fats are the ones saturated with hydrogen atoms. Unsaturated fats have "gaps" where hydrogens are missing because double bonds have formed between the carbons.
• D is incorrect: This is chemically impossible. Saturated fats, by definition, have zero double bonds. Furthermore, because unsaturated fats have double bonds, they actually have fewer hydrogen atoms than saturated fats of the same length.

TEAS Concept: Lipids and Bonding

On the TEAS, you need to know that:

1. Saturated Fats: No double bonds ($C-C$). They are straight, pack tightly, and are usually animal-derived solids at room temperature.
2. Unsaturated Fats: One or more double bonds ($C=C$). These double bonds create "kinks" or bends in the chain. These bends prevent tight packing, which is why they are usually plant-derived liquids (oils) at room temperature.

Study Tip: The "S" Rule

To keep these straight on test day, remember the three S's: Saturated fats have Single bonds and are Solid at room temperature. If it's not "S," it's probably unsaturated!