The transport of oxygen by blood is facilitated by a specific type of blood cell called erythrocytes, also known as red blood cells. Erythrocytes are specialized cells that contain a protein called hemoglobin, which binds to oxygen and carries it throughout the body.

Option 1, erythrocytes, is the correct answer because they are specifically designed for the transport of oxygen. They have a unique structure that allows them to carry a large amount of hemoglobin, which increases their capacity to transport oxygen.

Option 2, thrombocytes, also known as platelets, are involved in blood clotting and do not play a direct role in the transport of oxygen.

Option 3, lymphocytes, are a type of white blood cell that is primarily involved in the immune response and not involved in transporting oxygen.

Option 4, leukocytes, which are different types of white blood cells, are primarily responsible for fighting infections and do not directly participate in the transport of oxygen.

Therefore, the correct answer is option 1, erythrocytes, as they are specifically designed for the transport of oxygen through the bloodstream.