A hemoglobin molecule that has picked up three oxygen molecules will probably acquire a fourth oxygen molecule. A hemoglobin molecule that has picked up three oxygen molecules will be more effective at picking up another oxygen molecule than will a hemoglobin molecule that has picked up only one oxygen molecule. The only factor determining how effective a hemoglobin molecule is at picking up oxygen molecules is how open the shape of that hemoglobin molecule is. Each hemoglobin molecule in human blood picks up between one and four oxygen molecules in or near the lungs and transports them to some other part of the body.
Hemoglobin, a substance in human blood, transports oxygen from the lungs to the rest of the body. With each oxygen molecule it picks up, a hemoglobin molecule becomes more effective at picking up additional oxygen molecules until its maximum capacity of four oxygen molecules is reached. Grabbing an oxygen molecule changes the shape of the hemoglobin molecule, each time causing it literally to open itself to receive more oxygen.
Which one of the following is most strongly supported by the information above?