Question 21

Hemoglobin is a protein.

Hemoglobin is a protein found in red blood cells that is responsible for transporting oxygen throughout the body. It is composed of amino acids, which are the building blocks of proteins.

A) cellulose

Cellulose is a carbohydrate, specifically a polysaccharide, that provides structural support in plant cell walls. It is not a protein, as it does not consist of amino acids and does not perform the functions associated with proteins.

B) hemoglobin

Hemoglobin is indeed a protein that plays a crucial role in the respiratory system by binding to oxygen and facilitating its transport in the bloodstream. Its structure is made up of multiple polypeptide chains and is vital for life, making it the correct answer.

C) estrogen

Estrogen is a steroid hormone that plays a significant role in the regulation of the female reproductive system and secondary sexual characteristics. Although it is biologically active in the body, it is not classified as a protein.

D) ATP

Adenosine triphosphate (ATP) is a nucleotide that serves as the primary energy carrier in cells. While it is essential for various biochemical processes, it is not a protein, as it does not consist of amino acids.

Conclusion

Hemoglobin is the only correct answer as it is a protein essential for oxygen transport in the body, while the other options represent carbohydrates, hormones, and nucleotides that do not fit the definition of proteins. Each of the incorrect options serves different biological functions but lacks the structural and functional characteristics that define proteins.