Which statement best describes the general role of transport proteins?

• A. They catalyze chemical reactions
• B. They carry substances within the organism (for example, hemoglobin)
• C. They provide structural stability
• D. They regulate when and where genes are expressed

Answer: (B)

Transport proteins move substances around the body by binding specific molecules and helping them get from one place to another. Hemoglobin is a classic example: it binds oxygen in the lungs, carries it through the bloodstream, and releases it where it’s needed, and it also helps carry carbon dioxide back for disposal. This movement and delivery role is what defines transport proteins.

This differs from enzymes, which speed up chemical reactions; structural proteins, which provide support and shape to cells and tissues; and regulatory proteins, which control when and where genes are expressed. So the general function of transport proteins is to shuttle substances to their destinations within the organism.